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  • richardmitnick 9:09 am on September 1, 2021 Permalink | Reply
    Tags: "An Accidental Discovery Hints at a Hidden Population of Cosmic Objects", "The Accident" might be 10 billion to 13 billion years old., A peculiar cosmic object called WISEA J153429.75-104303.3 – nicknamed “The Accident”, , , Brown Dwarfs, , ,   

    From NASA JPL-Caltech (US) : “An Accidental Discovery Hints at a Hidden Population of Cosmic Objects” 

    NASA JPL Banner

    From NASA JPL-Caltech (US)

    Aug 31, 2021

    Calla Cofield
    Jet Propulsion Laboratory, Pasadena, Calif.
    626-808-2469
    calla.e.cofield@jpl.nasa.gov

    1
    This mosaic shows the entire sky imaged by the Wide-field Infrared Survey Explorer (WISE) [below]. Infrared light refers to wavelengths that are longer than those visible to the human eye. Many cosmic objects radiate infrared, including gas and dust clouds where stars form, and brown dwarfs. Credit: NASA/JPL-Caltech/The University of California-Los Angeles (US).

    Brown dwarfs aren’t quite stars and aren’t quite planets, and a new study suggests there might be more of them lurking in our galaxy than scientists previously thought.

    A new study [below] offers a tantalizing explanation for how a peculiar cosmic object called WISEA J153429.75-104303.3 – nicknamed “The Accident” – came to be. “The Accident” is a brown dwarf. Though they form like stars, these objects don’t have enough mass to kickstart nuclear fusion, the process that causes stars to shine. And while brown dwarfs sometimes defy characterization, astronomers have a good grasp on their general characteristics.

    Or they did, until they found this one.

    “The Accident” got its name after being discovered by sheer luck. It slipped past normal searches because it doesn’t resemble any of the just over 2,000 brown dwarfs that have been found in our galaxy so far.

    2
    Can you see the dark spot moving in the bottom left corner of the screen? It’s a brown dwarf nicknamed “The Accident,” which was discovered by citizen scientist Dan Caselden. It had slipped past typical searches because it doesn’t look like any other known brown dwarfs. Credit: Dan Caselden/ NASA/JPL-Caltech.

    As brown dwarfs age, they cool off, and their brightness in different wavelengths of light changes. It’s not unlike how some metals, when heated, go from bright white to deep red as they cool. The Accident confused scientists because it was faint in some key wavelengths, suggesting it was very cold (and old), but bright in others, indicating a higher temperature.

    “This object defied all our expectations,” said Davy Kirkpatrick, an astrophysicist at Caltech IPAC-Infrared Processing and Analysis Center (US) in Pasadena, California. He and his co-authors posit in their new study, appearing in The Astrophysical Journal Letters, that “The Accident” might be 10 billion to 13 billion years old – at least double the median age of other known brown dwarfs. That means it would have formed when our galaxy was much younger and had a different chemical makeup. If that’s the case, there are likely many more of these ancient brown dwarfs lurking in our galactic neighborhood.

    A Peculiar Profile

    “The Accident” was first spotted by NASA’s Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE), launched in 2009 under the moniker WISE and managed by NASA’s Jet Propulsion Laboratory in Southern California.

    Because brown dwarfs are relatively cool objects, they radiate mostly infrared light, or wavelengths longer than what the human eye can see.

    3
    Brown dwarfs share certain characteristics with both stars and planets. Generally, they are less massive than stars and more massive than planets. A brown dwarf becomes a star if its core pressure gets high enough to start nuclear fusion, the process that causes stars to shine. Credit: NASA/JPL-Caltech.

    To figure out how “The Accident” could have such seemingly contradictory properties – some suggesting it is very cold, others indicating it is much warmer – the scientists needed more information. So they observed it in additional infrared wavelengths with a ground-based telescope at the W. M. Keck Observatory in Hawaii.

    But the brown dwarf appeared so faint in those wavelengths, they couldn’t detect it at all, apparently confirming their suggestion that it was very cold.

    They next set out to determine if the dimness resulted from “The Accident” being farther than expected from Earth. But that wasn’t the case, according to precise distance measurements by NASA’s Hubble and Spitzer Space Telescopes.

    Having determined the object’s distance – about 50 light-years from Earth – the team realized that it is moving fast – about half a million miles per hour (800,000 kph). That’s much faster than all other brown dwarfs known to be at this distance from Earth, which means it has probably been careening around the galaxy for a long time, encountering massive objects that accelerate it with their gravity.

    With a mound of evidence suggesting “The Accident” is extremely old, the researchers propose that its strange properties aren’t strange at all and that they may be a clue to its age.

    When the Milky Way formed about 13.6 billion years ago, it was composed almost entirely of hydrogen and helium. Other elements, like carbon, formed inside stars; when the most massive stars exploded as supernovae, they scattered the elements throughout the galaxy.

    Methane, composed of hydrogen and carbon, is common in most brown dwarfs that have a temperature similar to “The Accident”. But “The Accident’s” light profile suggests it contains very little methane. Like all molecules, methane absorbs specific wavelengths of light, so a methane-rich brown dwarf would be dim in those wavelengths. The Accident, by contrast, is bright in those wavelengths, which could indicate low levels of methane.

    Thus, the light profile of “The Accident” could match that of a very old brown dwarf that formed when the galaxy was still carbon poor; very little carbon at formation means very little methane in its atmosphere today.

    “It’s not a surprise to find a brown dwarf this old, but it is a surprise to find one in our backyard,” said Federico Marocco, an astrophysicist at IPAC at Caltech who led the new observations using the Keck and Hubble telescopes. “We expected that brown dwarfs this old exist, but we also expected them to be incredibly rare. The chance of finding one so close to the solar system could be a lucky coincidence, or it tells us that they’re more common than we thought.”

    A Lucky Accident

    To find more ancient brown dwarfs like “The Accident” – if they’re out there – researchers might have to change how they search for these objects.

    “The Accident” was discovered by citizen scientist Dan Caselden, who was using an online program he built to find brown dwarfs in NEOWISE data. The sky is full of objects that radiate infrared light; by and large, these objects appear to remain fixed in the sky, due to their great distance from Earth. But because brown dwarfs are so faint, they are visible only when they’re relatively close to Earth, and that means scientists can observe them moving across the sky over months or years. (NEOWISE maps the entire sky about once every six months.)

    Caselden’s program attempted to remove the stationary infrared objects (like distant stars) from the NEOWISE maps and highlight moving objects that had similar characteristics to known brown dwarfs. He was looking at one such brown dwarf candidate when he spotted another, much fainter object moving quickly across the screen. This would turn out to be WISEA J153429.75-104303.3, which hadn’t been highlighted because it did not match the program’s profile of a brown dwarf. Caselden caught it by accident.

    “This discovery is telling us that there’s more variety in brown dwarf compositions than we’ve seen so far,” said Kirkpatrick. “There are likely more weird ones out there, and we need to think about how to look for them.”

    More About the Missions

    Launched in 2009, the WISE spacecraft was placed into hibernation in 2011 after completing its primary mission. In September 2013, NASA reactivated the spacecraft with the primary goal of scanning for near-Earth objects, or NEOs, and the mission and spacecraft were renamed NEOWISE. JPL, a division of Caltech, managed and operated WISE for NASA’s Science Mission Directorate (SMD). The mission was selected competitively under NASA’s Explorers Program (US) managed by the agency’s Goddard Space Flight Center in Greenbelt, Maryland. NEOWISE is a project of JPL, a division of Caltech, and The University of Arizona (US), supported by NASA’s Planetary Defense Coordination Office (US).

    For more information about WISE, go to:

    https://www.nasa.gov/mission_pages/WISE/main/index.html

    JPL managed Spitzer mission operations for NASA’s SMD until the spacecraft was retired in 2020. Science operations were conducted at the Spitzer Science Center (US) at IPAC at Caltech. Spacecraft operations were based at Lockheed Martin Space in Littleton, Colorado. The Spitzer data archive is housed at the Infrared Science Archive at IPAC at Caltech.

    For more information about NASA’s Spitzer mission, go to:

    https://www.nasa.gov/mission_pages/spitzer/main/index.html

    https://www.ipac.caltech.edu/project/spitzer

    The Hubble Space Telescope is a project of international cooperation between NASA and European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI)(US) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the AURA-Assocation of Universities for Research in Astronomy (US) in Washington.

    For more information about NASA’s Hubble, go to:

    https://www.nasa.gov/mission_pages/hubble/main/index.html

    For more opportunities to participate in NASA Citizen Science Projects, go to:

    https://science.nasa.gov/citizenscience

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) (US) ) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge, on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration (US). The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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  • richardmitnick 8:50 pm on June 9, 2021 Permalink | Reply
    Tags: , 2MASS J22081363+29212 is a sizzling 2780 degrees Fahrenheit (1527 degrees Celsius)., Brown Dwarfs, Brown Dwarfs-up to 80 times Jupiter's mass., , The free-floating brown dwarf known as 2MASS J22081363+2921215., While they're cooler than bona fide stars brown dwarfs are still extremely hot.   

    From NASA/ESA Hubble Telescope: Women in STEM-Elena Manjavacas “Astronomers Probe Layer-Cake Structure of Brown Dwarf’s Atmosphere” 

    From NASA/ESA Hubble Telescope

    June 09, 2021

    Credits:
    MEDIA CONTACT:
    Donna Weaver
    Space Telescope Science Institute, Baltimore, Maryland

    Christine Pulliam
    Space Telescope Science Institute, Baltimore, Maryland

    SCIENCE CONTACT:
    Elena Manjavacas
    Space Telescope Science Institute, Baltimore, Maryland

    1
    About This Image
    Observations of a nearby brown dwarf suggest that it has a mottled atmosphere with scattered clouds and mysterious dark spots reminiscent of Jupiter’s Great Red Spot, as shown in this artist’s concept. The nomadic object, called 2MASS J22081363+2921215, resembles a carved Halloween pumpkin, with light escaping from its hot interior. Brown dwarfs are more massive than planets but too small to sustain nuclear fusion, which powers stars.
    Though only roughly 115 light-years away, the brown dwarf is too distant for any features to be photographed. Instead, researchers used the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) at the W. M. Keck Observatory in Hawaii to study the colors and brightness variations of the brown dwarf’s layer-cake cloud structure, as seen in near-infrared light. MOSFIRE also collected the spectral fingerprints of various chemical elements contained in the clouds and how they change with time.

    Credits: Leah Hustak (Space Telescope Science Institute (US)) National Aeronautics Space Agency (US), European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU).

    2
    About This Image
    This graphic shows successive layers of clouds in the atmosphere of a nearby, free-floating brown dwarf. Breaks in the upper cloud layers allowed astronomers to probe deeper into the atmosphere of the brown dwarf called 2MASS J22081363+2921215. Brown dwarfs are more massive than planets but too small to sustain nuclear fusion, which powers stars.
    This illustration is based on infrared observations of the clouds’ colors and brightness variations, as well as the spectral fingerprints of various chemical elements contained in the clouds and atmospheric modeling.

    Credits:Andi James (STScI), NASA, ESA.

    Summary
    Observations May Offer Insight into the Atmospheres of Giant Planets

    Brown dwarfs are the cosmic equivalent of tweeners. They’re too massive to be planets and too small to sustain nuclear fusion in their cores, which powers stars. Many brown dwarfs are nomadic. They do not orbit stars but drift among them as loners.

    Astronomers would like to know how these wayward objects are put together. Do they share any kind of kinship with bloated gas-giant planets like Jupiter? Studying brown dwarfs is much more difficult than studying nearby Jupiter for making comparisons. We can send spacecraft to Jupiter. But astronomers need to look across many light-years to peer down into a brown dwarf’s atmosphere.

    Researchers used the giant W. M. Keck Observatory in Hawaii to observe a nearby brown dwarf in infrared light.

    Unlike Jupiter, the young brown dwarf is still so hot it glows from the inside out, and looks like a carved Halloween pumpkin. Because the brown dwarf has scattered clouds, light shining up from deep down in the dwarf’s atmosphere fluctuates, which the researchers measured. They found that the dwarf’s atmosphere has a layer-cake structure with clouds having different composition at different altitudes.
    ______________________________________________________________________________________________________________

    Jupiter may be the bully planet of our solar system because it’s the most massive planet. But it’s actually a runt compared to many of the giant planets found around other stars.

    These alien worlds, called super-Jupiters, weigh up to 13 times Jupiter’s mass. Astronomers have analyzed the composition of some of these monsters. But it has been difficult to study their atmospheres in detail because these gas giants get lost in the glare of their parent stars.

    Researchers, however, have a substitute: the atmospheres of brown dwarfs, so-called failed stars that are up to 80 times Jupiter’s mass. These hefty objects form out of a collapsing cloud of gas, as stars do, but lack the mass to become hot enough to sustain nuclear fusion in their cores, which powers stars.

    Instead, brown dwarfs share a kinship with super-Jupiters. Both types of objects have similar temperatures and are extremely massive. They also have complex, varied atmospheres. The only difference, astronomers think, is their pedigree. Super-Jupiters form around stars; brown dwarfs often form in isolation.

    A team of astronomers, led by Elena Manjavacas of the Space Telescope Science Institute in Baltimore, Maryland, has tested a new way to peer through the cloud layers of these nomadic objects. The researchers used an instrument at the W. M. Keck Observatory, MaunaKea, Hawai’i (US) in Hawaii to study in near-infrared light the colors and brightness variations of the layer-cake cloud structure in the nearby, free-floating brown dwarf known as 2MASS J22081363+2921215.

    The Keck Observatory instrument, called the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE), also analyzed the spectral fingerprints of various chemical elements contained in the clouds and how they change with time.

    This is the first time astronomers have used the MOSFIRE instrument in this type of study.

    These measurements offered Manjavacas a holistic view of the brown dwarf’s atmospheric clouds, providing more detail than previous observations of this object. Pioneered by Hubble observations, this technique is difficult for ground-based telescopes to do because of contamination from Earth’s atmosphere, which absorbs certain infrared wavelengths. This absorption rate changes due to the weather.

    “The only way to do this from the ground is using the high-resolution MOSFIRE instrument because it allows us to observe multiple stars simultaneously with our brown dwarf,” Manjavacas explained. “This allows us to correct for the contamination introduced by the Earth’s atmosphere and measure the true signal from the brown dwarf with good precision. So, these observations are a proof-of-concept that MOSFIRE can do these types of studies of brown-dwarf atmospheres.”

    Manjavacas will present her results June 9 in a press conference at the virtual meeting of the American Astronomical Society (US).

    The researcher decided to study this particular brown dwarf because it is very young and therefore extremely bright and has not cooled off yet. Its mass and temperature are similar to those of the nearby giant exoplanet Beta Pictoris b, discovered in 2008 near-infrared images taken by the European Southern Observatory’s Very Large Telescope in northern Chile.

    “We don’t have the ability yet with current technology to analyze in detail the atmosphere of Beta Pictoris b,” Manjavacas said. “So, we’re using our study of this brown dwarf’s atmosphere as a proxy to get an idea of what the exoplanet’s clouds might look like at different heights of its atmosphere.”

    Both the brown dwarf and Beta Pictoris b are young, so they radiate heat strongly in the near-infrared. They are both members of a flock of stars and sub-stellar objects called the Beta Pictoris moving group, which shares the same origin and a common motion through space. The group, which is about 33 million years old, is the closest grouping of young stars to Earth. It is located roughly 115 light-years away.

    While they’re cooler than bona fide stars brown dwarfs are still extremely hot. The brown dwarf in Manjavacas’ study is a sizzling 2,780 degrees Fahrenheit (1,527 degrees Celsius).

    The giant object is about 12 times heavier than Jupiter. As a young body, it is spinning incredibly fast, completing a rotation every 3.5 hours, compared to Jupiter’s 10-hour rotation period. So, clouds are whipping it, creating a dynamic, turbulent atmosphere.

    Keck Observatory’s MOSFIRE instrument stared at the brown dwarf for 2.5 hours, watching how the light filtering up through the atmosphere from the dwarf’s hot interior brightens and dims over time. Bright spots that appear on the rotating object indicate regions where researchers can see deeper into the atmosphere, where it is hotter. Infrared wavelengths allow astronomers to peer deeper into the atmosphere. The observations suggest the brown dwarf has a mottled atmosphere with scattered clouds. If viewed close-up, it might resemble a carved Halloween pumpkin, with light escaping from its hot interior.

    Its spectrum reveals clouds of hot sand grains and other exotic elements. Potassium iodide traces the object’s upper atmosphere, which also includes magnesium silicate clouds. Moving down in the atmosphere is a layer of sodium iodide and magnesium silicate clouds. The final layer consists of aluminum oxide clouds. The atmosphere’s total depth is 446 miles (718 kilometers). The elements detected represent a typical part of the composition of brown dwarf atmospheres, Manjavacas said.

    The researcher and her team used computer models of brown dwarf atmospheres to determine the location of the chemical compounds in each cloud layer.

    Manjavacas’ plan is to use Keck Observatory’s MOSFIRE to study other atmospheres of brown dwarfs and compare them to those of gas giants. Future telescopes such as NASA’s James Webb Space Telescope, an infrared observatory scheduled to launch later this year, will provide even more information about a brown dwarf’s atmosphere.

    “JWST will give us the structure of the entire atmosphere, providing more coverage than any other telescope,” Manjavacas said.

    The researcher hopes that MOSFIRE can be used in tandem with JWST to sample a wide range of brown dwarfs. The goal is a better understanding of brown dwarfs and giant planets.

    See the full article here.

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    Please help promote STEM in your local schools.

    Stem Education Coalition
    The NASA/ESA Hubble Space Telescope is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versatile, renowned both as a vital research tool and as a public relations boon for astronomy. The Hubble telescope is named after astronomer Edwin Hubble and is one of NASA’s Great Observatories, along with the NASA Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the NASA Spitzer Infared Space Telescope.



    Edwin Hubble at Caltech Palomar Samuel Oschin 48 inch Telescope(US). Credit: Emilio Segre Visual Archives/AIP/SPL).

    Hubble features a 2.4-meter (7.9 ft) mirror, and its four main instruments observe in the ultraviolet, visible, and near-infrared regions of the electromagnetic spectrum. Hubble’s orbit outside the distortion of Earth’s atmosphere allows it to capture extremely high-resolution images with substantially lower background light than ground-based telescopes. It has recorded some of the most detailed visible light images, allowing a deep view into space. Many Hubble observations have led to breakthroughs in astrophysics, such as determining the rate of expansion of the universe.

    The Hubble telescope was built by the United States space agency National Aeronautics Space Agency(US) with contributions from the European Space Agency [Agence spatiale européenne](EU). The Space Telescope Science Institute (STScI) selects Hubble’s targets and processes the resulting data, while the NASA Goddard Space Flight Center(US) controls the spacecraft. Space telescopes were proposed as early as 1923. Hubble was funded in the 1970s with a proposed launch in 1983, but the project was beset by technical delays, budget problems, and the 1986 Challenger disaster. It was finally launched by Space Shuttle Discovery in 1990, but its main mirror had been ground incorrectly, resulting in spherical aberration that compromised the telescope’s capabilities. The optics were corrected to their intended quality by a servicing mission in 1993.

    Hubble is the only telescope designed to be maintained in space by astronauts. Five Space Shuttle missions have repaired, upgraded, and replaced systems on the telescope, including all five of the main instruments. The fifth mission was initially canceled on safety grounds following the Columbia disaster (2003), but NASA administrator Michael D. Griffin approved the fifth servicing mission which was completed in 2009. The telescope was still operating as of April 24, 2020, its 30th anniversary, and could last until 2030–2040. One successor to the Hubble telescope is the National Aeronautics Space Agency(USA)/European Space Agency [Agence spatiale européenne](EU)/Canadian Space Agency(CA) Webb Infrared Space Telescope scheduled for launch in October 2021.

    Proposals and precursors

    In 1923, Hermann Oberth—considered a father of modern rocketry, along with Robert H. Goddard and Konstantin Tsiolkovsky—published Die Rakete zu den Planetenräumen (“The Rocket into Planetary Space“), which mentioned how a telescope could be propelled into Earth orbit by a rocket.

    The history of the Hubble Space Telescope can be traced back as far as 1946, to astronomer Lyman Spitzer’s paper entitled Astronomical advantages of an extraterrestrial observatory. In it, he discussed the two main advantages that a space-based observatory would have over ground-based telescopes. First, the angular resolution (the smallest separation at which objects can be clearly distinguished) would be limited only by diffraction, rather than by the turbulence in the atmosphere, which causes stars to twinkle, known to astronomers as seeing. At that time ground-based telescopes were limited to resolutions of 0.5–1.0 arcseconds, compared to a theoretical diffraction-limited resolution of about 0.05 arcsec for an optical telescope with a mirror 2.5 m (8.2 ft) in diameter. Second, a space-based telescope could observe infrared and ultraviolet light, which are strongly absorbed by the atmosphere.

    Spitzer devoted much of his career to pushing for the development of a space telescope. In 1962, a report by the U.S. National Academy of Sciences recommended development of a space telescope as part of the space program, and in 1965 Spitzer was appointed as head of a committee given the task of defining scientific objectives for a large space telescope.

    Space-based astronomy had begun on a very small scale following World War II, as scientists made use of developments that had taken place in rocket technology. The first ultraviolet spectrum of the Sun was obtained in 1946, and the National Aeronautics and Space Administration (US) launched the Orbiting Solar Observatory (OSO) to obtain UV, X-ray, and gamma-ray spectra in 1962.

    An orbiting solar telescope was launched in 1962 by the United Kingdom as part of the Ariel space program, and in 1966 NASA launched the first Orbiting Astronomical Observatory (OAO) mission. OAO-1’s battery failed after three days, terminating the mission. It was followed by OAO-2, which carried out ultraviolet observations of stars and galaxies from its launch in 1968 until 1972, well beyond its original planned lifetime of one year.

    The OSO and OAO missions demonstrated the important role space-based observations could play in astronomy. In 1968, NASA developed firm plans for a space-based reflecting telescope with a mirror 3 m (9.8 ft) in diameter, known provisionally as the Large Orbiting Telescope or Large Space Telescope (LST), with a launch slated for 1979. These plans emphasized the need for crewed maintenance missions to the telescope to ensure such a costly program had a lengthy working life, and the concurrent development of plans for the reusable Space Shuttle indicated that the technology to allow this was soon to become available.

    Quest for funding

    The continuing success of the OAO program encouraged increasingly strong consensus within the astronomical community that the LST should be a major goal. In 1970, NASA established two committees, one to plan the engineering side of the space telescope project, and the other to determine the scientific goals of the mission. Once these had been established, the next hurdle for NASA was to obtain funding for the instrument, which would be far more costly than any Earth-based telescope. The U.S. Congress questioned many aspects of the proposed budget for the telescope and forced cuts in the budget for the planning stages, which at the time consisted of very detailed studies of potential instruments and hardware for the telescope. In 1974, public spending cuts led to Congress deleting all funding for the telescope project.
    In response a nationwide lobbying effort was coordinated among astronomers. Many astronomers met congressmen and senators in person, and large scale letter-writing campaigns were organized. The National Academy of Sciences published a report emphasizing the need for a space telescope, and eventually the Senate agreed to half the budget that had originally been approved by Congress.

    The funding issues led to something of a reduction in the scale of the project, with the proposed mirror diameter reduced from 3 m to 2.4 m, both to cut costs and to allow a more compact and effective configuration for the telescope hardware. A proposed precursor 1.5 m (4.9 ft) space telescope to test the systems to be used on the main satellite was dropped, and budgetary concerns also prompted collaboration with the European Space Agency. ESA agreed to provide funding and supply one of the first generation instruments for the telescope, as well as the solar cells that would power it, and staff to work on the telescope in the United States, in return for European astronomers being guaranteed at least 15% of the observing time on the telescope. Congress eventually approved funding of US$36 million for 1978, and the design of the LST began in earnest, aiming for a launch date of 1983. In 1983 the telescope was named after Edwin Hubble, who confirmed one of the greatest scientific discoveries of the 20th century, made by Georges Lemaître, that the universe is expanding.

    Construction and engineering

    Once the Space Telescope project had been given the go-ahead, work on the program was divided among many institutions. NASA Marshall Space Flight Center (MSFC) was given responsibility for the design, development, and construction of the telescope, while Goddard Space Flight Center was given overall control of the scientific instruments and ground-control center for the mission. MSFC commissioned the optics company Perkin-Elmer to design and build the Optical Telescope Assembly (OTA) and Fine Guidance Sensors for the space telescope. Lockheed was commissioned to construct and integrate the spacecraft in which the telescope would be housed.

    Optical Telescope Assembly

    Optically, the HST is a Cassegrain reflector of Ritchey–Chrétien design, as are most large professional telescopes. This design, with two hyperbolic mirrors, is known for good imaging performance over a wide field of view, with the disadvantage that the mirrors have shapes that are hard to fabricate and test. The mirror and optical systems of the telescope determine the final performance, and they were designed to exacting specifications. Optical telescopes typically have mirrors polished to an accuracy of about a tenth of the wavelength of visible light, but the Space Telescope was to be used for observations from the visible through the ultraviolet (shorter wavelengths) and was specified to be diffraction limited to take full advantage of the space environment. Therefore, its mirror needed to be polished to an accuracy of 10 nanometers, or about 1/65 of the wavelength of red light. On the long wavelength end, the OTA was not designed with optimum IR performance in mind—for example, the mirrors are kept at stable (and warm, about 15 °C) temperatures by heaters. This limits Hubble’s performance as an infrared telescope.

    Perkin-Elmer intended to use custom-built and extremely sophisticated computer-controlled polishing machines to grind the mirror to the required shape. However, in case their cutting-edge technology ran into difficulties, NASA demanded that PE sub-contract to Kodak to construct a back-up mirror using traditional mirror-polishing techniques. (The team of Kodak and Itek also bid on the original mirror polishing work. Their bid called for the two companies to double-check each other’s work, which would have almost certainly caught the polishing error that later caused such problems.) The Kodak mirror is now on permanent display at the National Air and Space Museum. An Itek mirror built as part of the effort is now used in the 2.4 m telescope at the Magdalena Ridge Observatory.

    Construction of the Perkin-Elmer mirror began in 1979, starting with a blank manufactured by Corning from their ultra-low expansion glass. To keep the mirror’s weight to a minimum it consisted of top and bottom plates, each one inch (25 mm) thick, sandwiching a honeycomb lattice. Perkin-Elmer simulated microgravity by supporting the mirror from the back with 130 rods that exerted varying amounts of force. This ensured the mirror’s final shape would be correct and to specification when finally deployed. Mirror polishing continued until May 1981. NASA reports at the time questioned Perkin-Elmer’s managerial structure, and the polishing began to slip behind schedule and over budget. To save money, NASA halted work on the back-up mirror and put the launch date of the telescope back to October 1984. The mirror was completed by the end of 1981; it was washed using 2,400 US gallons (9,100 L) of hot, deionized water and then received a reflective coating of 65 nm-thick aluminum and a protective coating of 25 nm-thick magnesium fluoride.

    Doubts continued to be expressed about Perkin-Elmer’s competence on a project of this importance, as their budget and timescale for producing the rest of the OTA continued to inflate. In response to a schedule described as “unsettled and changing daily”, NASA postponed the launch date of the telescope until April 1985. Perkin-Elmer’s schedules continued to slip at a rate of about one month per quarter, and at times delays reached one day for each day of work. NASA was forced to postpone the launch date until March and then September 1986. By this time, the total project budget had risen to US$1.175 billion.

    Spacecraft systems

    The spacecraft in which the telescope and instruments were to be housed was another major engineering challenge. It would have to withstand frequent passages from direct sunlight into the darkness of Earth’s shadow, which would cause major changes in temperature, while being stable enough to allow extremely accurate pointing of the telescope. A shroud of multi-layer insulation keeps the temperature within the telescope stable and surrounds a light aluminum shell in which the telescope and instruments sit. Within the shell, a graphite-epoxy frame keeps the working parts of the telescope firmly aligned. Because graphite composites are hygroscopic, there was a risk that water vapor absorbed by the truss while in Lockheed’s clean room would later be expressed in the vacuum of space; resulting in the telescope’s instruments being covered by ice. To reduce that risk, a nitrogen gas purge was performed before launching the telescope into space.

    While construction of the spacecraft in which the telescope and instruments would be housed proceeded somewhat more smoothly than the construction of the OTA, Lockheed still experienced some budget and schedule slippage, and by the summer of 1985, construction of the spacecraft was 30% over budget and three months behind schedule. An MSFC report said Lockheed tended to rely on NASA directions rather than take their own initiative in the construction.

    Computer systems and data processing

    The two initial, primary computers on the HST were the 1.25 MHz DF-224 system, built by Rockwell Autonetics, which contained three redundant CPUs, and two redundant NSSC-1 (NASA Standard Spacecraft Computer, Model 1) systems, developed by Westinghouse and GSFC using diode–transistor logic (DTL). A co-processor for the DF-224 was added during Servicing Mission 1 in 1993, which consisted of two redundant strings of an Intel-based 80386 processor with an 80387 math co-processor. The DF-224 and its 386 co-processor were replaced by a 25 MHz Intel-based 80486 processor system during Servicing Mission 3A in 1999. The new computer is 20 times faster, with six times more memory, than the DF-224 it replaced. It increases throughput by moving some computing tasks from the ground to the spacecraft and saves money by allowing the use of modern programming languages.

    Additionally, some of the science instruments and components had their own embedded microprocessor-based control systems. The MATs (Multiple Access Transponder) components, MAT-1 and MAT-2, utilize Hughes Aircraft CDP1802CD microprocessors. The Wide Field and Planetary Camera (WFPC) also utilized an RCA 1802 microprocessor (or possibly the older 1801 version). The WFPC-1 was replaced by the WFPC-2 [below] during Servicing Mission 1 in 1993, which was then replaced by the Wide Field Camera 3 (WFC3) [below] during Servicing Mission 4 in 2009.

    Initial instruments

    When launched, the HST carried five scientific instruments: the Wide Field and Planetary Camera (WF/PC), Goddard High Resolution Spectrograph (GHRS), High Speed Photometer (HSP), Faint Object Camera (FOC) and the Faint Object Spectrograph (FOS). WF/PC was a high-resolution imaging device primarily intended for optical observations. It was built by NASA JPL-Caltech(US), and incorporated a set of 48 filters isolating spectral lines of particular astrophysical interest. The instrument contained eight charge-coupled device (CCD) chips divided between two cameras, each using four CCDs. Each CCD has a resolution of 0.64 megapixels. The wide field camera (WFC) covered a large angular field at the expense of resolution, while the planetary camera (PC) took images at a longer effective focal length than the WF chips, giving it a greater magnification.

    The GHRS was a spectrograph designed to operate in the ultraviolet. It was built by the Goddard Space Flight Center and could achieve a spectral resolution of 90,000. Also optimized for ultraviolet observations were the FOC and FOS, which were capable of the highest spatial resolution of any instruments on Hubble. Rather than CCDs these three instruments used photon-counting digicons as their detectors. The FOC was constructed by ESA, while the University of California, San Diego(US), and Martin Marietta Corporation built the FOS.

    The final instrument was the HSP, designed and built at the University of Wisconsin–Madison(US). It was optimized for visible and ultraviolet light observations of variable stars and other astronomical objects varying in brightness. It could take up to 100,000 measurements per second with a photometric accuracy of about 2% or better.

    HST’s guidance system can also be used as a scientific instrument. Its three Fine Guidance Sensors (FGS) are primarily used to keep the telescope accurately pointed during an observation, but can also be used to carry out extremely accurate astrometry; measurements accurate to within 0.0003 arcseconds have been achieved.

    Ground support

    The Space Telescope Science Institute (STScI) is responsible for the scientific operation of the telescope and the delivery of data products to astronomers. STScI is operated by the Association of Universities for Research in Astronomy(US) (AURA) and is physically located in Baltimore, Maryland on the Homewood campus of Johns Hopkins University(US), one of the 39 U.S. universities and seven international affiliates that make up the AURA consortium. STScI was established in 1981 after something of a power struggle between NASA and the scientific community at large. NASA had wanted to keep this function in-house, but scientists wanted it to be based in an academic establishment. The Space Telescope European Coordinating Facility (ST-ECF), established at Garching bei München near Munich in 1984, provided similar support for European astronomers until 2011, when these activities were moved to the European Space Astronomy Centre.

    One rather complex task that falls to STScI is scheduling observations for the telescope. Hubble is in a low-Earth orbit to enable servicing missions, but this means most astronomical targets are occulted by the Earth for slightly less than half of each orbit. Observations cannot take place when the telescope passes through the South Atlantic Anomaly due to elevated radiation levels, and there are also sizable exclusion zones around the Sun (precluding observations of Mercury), Moon and Earth. The solar avoidance angle is about 50°, to keep sunlight from illuminating any part of the OTA. Earth and Moon avoidance keeps bright light out of the FGSs, and keeps scattered light from entering the instruments. If the FGSs are turned off, the Moon and Earth can be observed. Earth observations were used very early in the program to generate flat-fields for the WFPC1 instrument. There is a so-called continuous viewing zone (CVZ), at roughly 90° to the plane of Hubble’s orbit, in which targets are not occulted for long periods.

    Challenger disaster, delays, and eventual launch

    By January 1986, the planned launch date of October looked feasible, but the Challenger explosion brought the U.S. space program to a halt, grounding the Shuttle fleet and forcing the launch of Hubble to be postponed for several years. The telescope had to be kept in a clean room, powered up and purged with nitrogen, until a launch could be rescheduled. This costly situation (about US$6 million per month) pushed the overall costs of the project even higher. This delay did allow time for engineers to perform extensive tests, swap out a possibly failure-prone battery, and make other improvements. Furthermore, the ground software needed to control Hubble was not ready in 1986, and was barely ready by the 1990 launch.

    Eventually, following the resumption of shuttle flights in 1988, the launch of the telescope was scheduled for 1990. On April 24, 1990, Space Shuttle Discovery successfully launched it during the STS-31 mission.

    From its original total cost estimate of about US$400 million, the telescope cost about US$4.7 billion by the time of its launch. Hubble’s cumulative costs were estimated to be about US$10 billion in 2010, twenty years after launch.

    List of Hubble instruments

    Hubble accommodates five science instruments at a given time, plus the Fine Guidance Sensors, which are mainly used for aiming the telescope but are occasionally used for scientific astrometry measurements. Early instruments were replaced with more advanced ones during the Shuttle servicing missions. COSTAR was a corrective optics device rather than a science instrument, but occupied one of the five instrument bays.
    Since the final servicing mission in 2009, the four active instruments have been ACS, COS, STIS and WFC3. NICMOS is kept in hibernation, but may be revived if WFC3 were to fail in the future.

    Advanced Camera for Surveys (ACS; 2002–present)
    Cosmic Origins Spectrograph (COS; 2009–present)
    Corrective Optics Space Telescope Axial Replacement (COSTAR; 1993–2009)
    Faint Object Camera (FOC; 1990–2002)
    Faint Object Spectrograph (FOS; 1990–1997)
    Fine Guidance Sensor (FGS; 1990–present)
    Goddard High Resolution Spectrograph (GHRS/HRS; 1990–1997)
    High Speed Photometer (HSP; 1990–1993)
    Near Infrared Camera and Multi-Object Spectrometer (NICMOS; 1997–present, hibernating since 2008)
    Space Telescope Imaging Spectrograph (STIS; 1997–present (non-operative 2004–2009))
    Wide Field and Planetary Camera (WFPC; 1990–1993)
    Wide Field and Planetary Camera 2 (WFPC2; 1993–2009)
    Wide Field Camera 3 (WFC3; 2009–present)

    Of the former instruments, three (COSTAR, FOS and WFPC2) are displayed in the Smithsonian National Air and Space Museum. The FOC is in the Dornier museum, Germany. The HSP is in the Space Place at the University of Wisconsin–Madison. The first WFPC was dismantled, and some components were then re-used in WFC3.

    Flawed mirror

    Within weeks of the launch of the telescope, the returned images indicated a serious problem with the optical system. Although the first images appeared to be sharper than those of ground-based telescopes, Hubble failed to achieve a final sharp focus and the best image quality obtained was drastically lower than expected. Images of point sources spread out over a radius of more than one arcsecond, instead of having a point spread function (PSF) concentrated within a circle 0.1 arcseconds (485 nrad) in diameter, as had been specified in the design criteria.

    Analysis of the flawed images revealed that the primary mirror had been polished to the wrong shape. Although it was believed to be one of the most precisely figured optical mirrors ever made, smooth to about 10 nanometers, the outer perimeter was too flat by about 2200 nanometers (about 1⁄450 mm or 1⁄11000 inch). This difference was catastrophic, introducing severe spherical aberration, a flaw in which light reflecting off the edge of a mirror focuses on a different point from the light reflecting off its center.

    The effect of the mirror flaw on scientific observations depended on the particular observation—the core of the aberrated PSF was sharp enough to permit high-resolution observations of bright objects, and spectroscopy of point sources was affected only through a sensitivity loss. However, the loss of light to the large, out-of-focus halo severely reduced the usefulness of the telescope for faint objects or high-contrast imaging. This meant nearly all the cosmological programs were essentially impossible, since they required observation of exceptionally faint objects. This led politicians to question NASA’s competence, scientists to rue the cost which could have gone to more productive endeavors, and comedians to make jokes about NASA and the telescope − in the 1991 comedy The Naked Gun 2½: The Smell of Fear, in a scene where historical disasters are displayed, Hubble is pictured with RMS Titanic and LZ 129 Hindenburg. Nonetheless, during the first three years of the Hubble mission, before the optical corrections, the telescope still carried out a large number of productive observations of less demanding targets. The error was well characterized and stable, enabling astronomers to partially compensate for the defective mirror by using sophisticated image processing techniques such as deconvolution.

    Origin of the problem

    A commission headed by Lew Allen, director of the Jet Propulsion Laboratory, was established to determine how the error could have arisen. The Allen Commission found that a reflective null corrector, a testing device used to achieve a properly shaped non-spherical mirror, had been incorrectly assembled—one lens was out of position by 1.3 mm (0.051 in). During the initial grinding and polishing of the mirror, Perkin-Elmer analyzed its surface with two conventional refractive null correctors. However, for the final manufacturing step (figuring), they switched to the custom-built reflective null corrector, designed explicitly to meet very strict tolerances. The incorrect assembly of this device resulted in the mirror being ground very precisely but to the wrong shape. A few final tests, using the conventional null correctors, correctly reported spherical aberration. But these results were dismissed, thus missing the opportunity to catch the error, because the reflective null corrector was considered more accurate.

    The commission blamed the failings primarily on Perkin-Elmer. Relations between NASA and the optics company had been severely strained during the telescope construction, due to frequent schedule slippage and cost overruns. NASA found that Perkin-Elmer did not review or supervise the mirror construction adequately, did not assign its best optical scientists to the project (as it had for the prototype), and in particular did not involve the optical designers in the construction and verification of the mirror. While the commission heavily criticized Perkin-Elmer for these managerial failings, NASA was also criticized for not picking up on the quality control shortcomings, such as relying totally on test results from a single instrument.

    Design of a solution

    Many feared that Hubble would be abandoned. The design of the telescope had always incorporated servicing missions, and astronomers immediately began to seek potential solutions to the problem that could be applied at the first servicing mission, scheduled for 1993. While Kodak had ground a back-up mirror for Hubble, it would have been impossible to replace the mirror in orbit, and too expensive and time-consuming to bring the telescope back to Earth for a refit. Instead, the fact that the mirror had been ground so precisely to the wrong shape led to the design of new optical components with exactly the same error but in the opposite sense, to be added to the telescope at the servicing mission, effectively acting as “spectacles” to correct the spherical aberration.

    The first step was a precise characterization of the error in the main mirror. Working backwards from images of point sources, astronomers determined that the conic constant of the mirror as built was −1.01390±0.0002, instead of the intended −1.00230. The same number was also derived by analyzing the null corrector used by Perkin-Elmer to figure the mirror, as well as by analyzing interferograms obtained during ground testing of the mirror.

    Because of the way the HST’s instruments were designed, two different sets of correctors were required. The design of the Wide Field and Planetary Camera 2, already planned to replace the existing WF/PC, included relay mirrors to direct light onto the four separate charge-coupled device (CCD) chips making up its two cameras. An inverse error built into their surfaces could completely cancel the aberration of the primary. However, the other instruments lacked any intermediate surfaces that could be figured in this way, and so required an external correction device.

    The Corrective Optics Space Telescope Axial Replacement (COSTAR) system was designed to correct the spherical aberration for light focused at the FOC, FOS, and GHRS. It consists of two mirrors in the light path with one ground to correct the aberration. To fit the COSTAR system onto the telescope, one of the other instruments had to be removed, and astronomers selected the High Speed Photometer to be sacrificed. By 2002, all the original instruments requiring COSTAR had been replaced by instruments with their own corrective optics. COSTAR was removed and returned to Earth in 2009 where it is exhibited at the National Air and Space Museum. The area previously used by COSTAR is now occupied by the Cosmic Origins Spectrograph.

    Servicing missions and new instruments

    Servicing Mission 1

    The first Hubble serving mission was scheduled for 1993 before the mirror problem was discovered. It assumed greater importance, as the astronauts would need to do extensive work to install corrective optics; failure would have resulted in either abandoning Hubble or accepting its permanent disability. Other components failed before the mission, causing the repair cost to rise to $500 million (not including the cost of the shuttle flight). A successful repair would help demonstrate the viability of building Space Station Alpha, however.

    STS-49 in 1992 demonstrated the difficulty of space work. While its rescue of Intelsat 603 received praise, the astronauts had taken possibly reckless risks in doing so. Neither the rescue nor the unrelated assembly of prototype space station components occurred as the astronauts had trained, causing NASA to reassess planning and training, including for the Hubble repair. The agency assigned to the mission Story Musgrave—who had worked on satellite repair procedures since 1976—and six other experienced astronauts, including two from STS-49. The first mission director since Project Apollo would coordinate a crew with 16 previous shuttle flights. The astronauts were trained to use about a hundred specialized tools.

    Heat had been the problem on prior spacewalks, which occurred in sunlight. Hubble needed to be repaired out of sunlight. Musgrave discovered during vacuum training, seven months before the mission, that spacesuit gloves did not sufficiently protect against the cold of space. After STS-57 confirmed the issue in orbit, NASA quickly changed equipment, procedures, and flight plan. Seven total mission simulations occurred before launch, the most thorough preparation in shuttle history. No complete Hubble mockup existed, so the astronauts studied many separate models (including one at the Smithsonian) and mentally combined their varying and contradictory details. Service Mission 1 flew aboard Endeavour in December 1993, and involved installation of several instruments and other equipment over ten days.

    Most importantly, the High Speed Photometer was replaced with the COSTAR corrective optics package, and WFPC was replaced with the Wide Field and Planetary Camera 2 (WFPC2) with an internal optical correction system. The solar arrays and their drive electronics were also replaced, as well as four gyroscopes in the telescope pointing system, two electrical control units and other electrical components, and two magnetometers. The onboard computers were upgraded with added coprocessors, and Hubble’s orbit was boosted.

    On January 13, 1994, NASA declared the mission a complete success and showed the first sharper images. The mission was one of the most complex performed up until that date, involving five long extra-vehicular activity periods. Its success was a boon for NASA, as well as for the astronomers who now had a more capable space telescope.

    Servicing Mission 2

    Servicing Mission 2, flown by Discovery in February 1997, replaced the GHRS and the FOS with the Space Telescope Imaging Spectrograph (STIS) and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), replaced an Engineering and Science Tape Recorder with a new Solid State Recorder, and repaired thermal insulation. NICMOS contained a heat sink of solid nitrogen to reduce the thermal noise from the instrument, but shortly after it was installed, an unexpected thermal expansion resulted in part of the heat sink coming into contact with an optical baffle. This led to an increased warming rate for the instrument and reduced its original expected lifetime of 4.5 years to about two years.

    Servicing Mission 3A

    Servicing Mission 3A, flown by Discovery, took place in December 1999, and was a split-off from Servicing Mission 3 after three of the six onboard gyroscopes had failed. The fourth failed a few weeks before the mission, rendering the telescope incapable of performing scientific observations. The mission replaced all six gyroscopes, replaced a Fine Guidance Sensor and the computer, installed a Voltage/temperature Improvement Kit (VIK) to prevent battery overcharging, and replaced thermal insulation blankets.

    Servicing Mission 3B

    Servicing Mission 3B flown by Columbia in March 2002 saw the installation of a new instrument, with the FOC (which, except for the Fine Guidance Sensors when used for astrometry, was the last of the original instruments) being replaced by the Advanced Camera for Surveys (ACS). This meant COSTAR was no longer required, since all new instruments had built-in correction for the main mirror aberration. The mission also revived NICMOS by installing a closed-cycle cooler and replaced the solar arrays for the second time, providing 30 percent more power.

    Servicing Mission 4

    Plans called for Hubble to be serviced in February 2005, but the Columbia disaster in 2003, in which the orbiter disintegrated on re-entry into the atmosphere, had wide-ranging effects on the Hubble program. NASA Administrator Sean O’Keefe decided all future shuttle missions had to be able to reach the safe haven of the International Space Station should in-flight problems develop. As no shuttles were capable of reaching both HST and the space station during the same mission, future crewed service missions were canceled. This decision was criticised by numerous astronomers who felt Hubble was valuable enough to merit the human risk. HST’s planned successor, the James Webb Telescope (JWST), as of 2004 was not expected to launch until at least 2011. A gap in space-observing capabilities between a decommissioning of Hubble and the commissioning of a successor was of major concern to many astronomers, given the significant scientific impact of HST. The consideration that JWST will not be located in low Earth orbit, and therefore cannot be easily upgraded or repaired in the event of an early failure, only made concerns more acute. On the other hand, many astronomers felt strongly that servicing Hubble should not take place if the expense were to come from the JWST budget.

    In January 2004, O’Keefe said he would review his decision to cancel the final servicing mission to HST, due to public outcry and requests from Congress for NASA to look for a way to save it. The National Academy of Sciences convened an official panel, which recommended in July 2004 that the HST should be preserved despite the apparent risks. Their report urged “NASA should take no actions that would preclude a space shuttle servicing mission to the Hubble Space Telescope”. In August 2004, O’Keefe asked Goddard Space Flight Center to prepare a detailed proposal for a robotic service mission. These plans were later canceled, the robotic mission being described as “not feasible”. In late 2004, several Congressional members, led by Senator Barbara Mikulski, held public hearings and carried on a fight with much public support (including thousands of letters from school children across the U.S.) to get the Bush Administration and NASA to reconsider the decision to drop plans for a Hubble rescue mission.

    The nomination in April 2005 of a new NASA Administrator, Michael D. Griffin, changed the situation, as Griffin stated he would consider a crewed servicing mission. Soon after his appointment Griffin authorized Goddard to proceed with preparations for a crewed Hubble maintenance flight, saying he would make the final decision after the next two shuttle missions. In October 2006 Griffin gave the final go-ahead, and the 11-day mission by Atlantis was scheduled for October 2008. Hubble’s main data-handling unit failed in September 2008, halting all reporting of scientific data until its back-up was brought online on October 25, 2008. Since a failure of the backup unit would leave the HST helpless, the service mission was postponed to incorporate a replacement for the primary unit.

    Servicing Mission 4 (SM4), flown by Atlantis in May 2009, was the last scheduled shuttle mission for HST. SM4 installed the replacement data-handling unit, repaired the ACS and STIS systems, installed improved nickel hydrogen batteries, and replaced other components including all six gyroscopes. SM4 also installed two new observation instruments—Wide Field Camera 3 (WFC3) and the Cosmic Origins Spectrograph (COS)—and the Soft Capture and Rendezvous System, which will enable the future rendezvous, capture, and safe disposal of Hubble by either a crewed or robotic mission. Except for the ACS’s High Resolution Channel, which could not be repaired and was disabled, the work accomplished during SM4 rendered the telescope fully functional.

    Major projects

    Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey [CANDELS]

    The survey “aims to explore galactic evolution in the early Universe, and the very first seeds of cosmic structure at less than one billion years after the Big Bang.” The CANDELS project site describes the survey’s goals as the following:

    The Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey is designed to document the first third of galactic evolution from z = 8 to 1.5 via deep imaging of more than 250,000 galaxies with WFC3/IR and ACS. It will also find the first Type Ia SNe beyond z > 1.5 and establish their accuracy as standard candles for cosmology. Five premier multi-wavelength sky regions are selected; each has multi-wavelength data from Spitzer and other facilities, and has extensive spectroscopy of the brighter galaxies. The use of five widely separated fields mitigates cosmic variance and yields statistically robust and complete samples of galaxies down to 109 solar masses out to z ~ 8.

    Frontier Fields program

    The program, officially named Hubble Deep Fields Initiative 2012, is aimed to advance the knowledge of early galaxy formation by studying high-redshift galaxies in blank fields with the help of gravitational lensing to see the “faintest galaxies in the distant universe”. The Frontier Fields web page describes the goals of the program being:

    To reveal hitherto inaccessible populations of z = 5–10 galaxies that are ten to fifty times fainter intrinsically than any presently known
    To solidify our understanding of the stellar masses and star formation histories of sub-L* galaxies at the earliest times
    To provide the first statistically meaningful morphological characterization of star forming galaxies at z > 5
    To find z > 8 galaxies stretched out enough by cluster lensing to discern internal structure and/or magnified enough by cluster lensing for spectroscopic follow-up.

    Cosmic Evolution Survey (COSMOS)

    The Cosmic Evolution Survey (COSMOS) is an astronomical survey designed to probe the formation and evolution of galaxies as a function of both cosmic time (redshift) and the local galaxy environment. The survey covers a two square degree equatorial field with spectroscopy and X-ray to radio imaging by most of the major space-based telescopes and a number of large ground based telescopes, making it a key focus region of extragalactic astrophysics. COSMOS was launched in 2006 as the largest project pursued by the Hubble Space Telescope at the time, and still is the largest continuous area of sky covered for the purposes of mapping deep space in blank fields, 2.5 times the area of the moon on the sky and 17 times larger than the largest of the CANDELS regions. The COSMOS scientific collaboration that was forged from the initial COSMOS survey is the largest and longest-running extragalactic collaboration, known for its collegiality and openness. The study of galaxies in their environment can be done only with large areas of the sky, larger than a half square degree. More than two million galaxies are detected, spanning 90% of the age of the Universe. The COSMOS collaboration is led by Caitlin Casey, Jeyhan Kartaltepe, and Vernesa Smolcic and involves more than 200 scientists in a dozen countries.

    Important discoveries

    Hubble has helped resolve some long-standing problems in astronomy, while also raising new questions. Some results have required new theories to explain them.

    Age of the universe

    Among its primary mission targets was to measure distances to Cepheid variable stars more accurately than ever before, and thus constrain the value of the Hubble constant, the measure of the rate at which the universe is expanding, which is also related to its age. Before the launch of HST, estimates of the Hubble constant typically had errors of up to 50%, but Hubble measurements of Cepheid variables in the Virgo Cluster and other distant galaxy clusters provided a measured value with an accuracy of ±10%, which is consistent with other more accurate measurements made since Hubble’s launch using other techniques. The estimated age is now about 13.7 billion years, but before the Hubble Telescope, scientists predicted an age ranging from 10 to 20 billion years.

    Expansion of the universe

    While Hubble helped to refine estimates of the age of the universe, it also cast doubt on theories about its future. Astronomers from the High-z Supernova Search Team and the Supernova Cosmology Project used ground-based telescopes and HST to observe distant supernovae and uncovered evidence that, far from decelerating under the influence of gravity, the expansion of the universe may in fact be accelerating. Three members of these two groups have subsequently been awarded Nobel Prizes for their discovery.

    Saul Perlmutter [The Supernova Cosmology Project] shared the 2006 Shaw Prize in Astronomy, the 2011 Nobel Prize in Physics, and the 2015 Breakthrough Prize in Fundamental Physics with Brian P. Schmidt and Adam Riess [The High-z Supernova Search Team] for providing evidence that the expansion of the universe is accelerating.

    The cause of this acceleration remains poorly understood; the most common cause attributed is Dark Energy.

    Black holes

    The high-resolution spectra and images provided by the HST have been especially well-suited to establishing the prevalence of black holes in the center of nearby galaxies. While it had been hypothesized in the early 1960s that black holes would be found at the centers of some galaxies, and astronomers in the 1980s identified a number of good black hole candidates, work conducted with Hubble shows that black holes are probably common to the centers of all galaxies. The Hubble programs further established that the masses of the nuclear black holes and properties of the galaxies are closely related. The legacy of the Hubble programs on black holes in galaxies is thus to demonstrate a deep connection between galaxies and their central black holes.

    Extending visible wavelength images

    A unique window on the Universe enabled by Hubble are the Hubble Deep Field, Hubble Ultra-Deep Field, and Hubble Extreme Deep Field images, which used Hubble’s unmatched sensitivity at visible wavelengths to create images of small patches of sky that are the deepest ever obtained at optical wavelengths. The images reveal galaxies billions of light years away, and have generated a wealth of scientific papers, providing a new window on the early Universe. The Wide Field Camera 3 improved the view of these fields in the infrared and ultraviolet, supporting the discovery of some of the most distant objects yet discovered, such as MACS0647-JD.

    The non-standard object SCP 06F6 was discovered by the Hubble Space Telescope in February 2006.

    On March 3, 2016, researchers using Hubble data announced the discovery of the farthest known galaxy to date: GN-z11. The Hubble observations occurred on February 11, 2015, and April 3, 2015, as part of the CANDELS/GOODS-North surveys.

    Solar System discoveries

    HST has also been used to study objects in the outer reaches of the Solar System, including the dwarf planets Pluto and Eris.

    The collision of Comet Shoemaker-Levy 9 with Jupiter in 1994 was fortuitously timed for astronomers, coming just a few months after Servicing Mission 1 had restored Hubble’s optical performance. Hubble images of the planet were sharper than any taken since the passage of Voyager 2 in 1979, and were crucial in studying the dynamics of the collision of a comet with Jupiter, an event believed to occur once every few centuries.

    During June and July 2012, U.S. astronomers using Hubble discovered Styx, a tiny fifth moon orbiting Pluto.

    In March 2015, researchers announced that measurements of aurorae around Ganymede, one of Jupiter’s moons, revealed that it has a subsurface ocean. Using Hubble to study the motion of its aurorae, the researchers determined that a large saltwater ocean was helping to suppress the interaction between Jupiter’s magnetic field and that of Ganymede. The ocean is estimated to be 100 km (60 mi) deep, trapped beneath a 150 km (90 mi) ice crust.

    From June to August 2015, Hubble was used to search for a Kuiper belt object (KBO) target for the New Horizons Kuiper Belt Extended Mission (KEM) when similar searches with ground telescopes failed to find a suitable target.

    This resulted in the discovery of at least five new KBOs, including the eventual KEM target, 486958 Arrokoth, that New Horizons performed a close fly-by of on January 1, 2019.

    In August 2020, taking advantage of a total lunar eclipse, astronomers using NASA’s Hubble Space Telescope have detected Earth’s own brand of sunscreen – ozone – in our atmosphere. This method simulates how astronomers and astrobiology researchers will search for evidence of life beyond Earth by observing potential “biosignatures” on exoplanets (planets around other stars).
    Hubble and ALMA image of MACS J1149.5+2223.

    Supernova reappearance

    On December 11, 2015, Hubble captured an image of the first-ever predicted reappearance of a supernova, dubbed “Refsdal”, which was calculated using different mass models of a galaxy cluster whose gravity is warping the supernova’s light. The supernova was previously seen in November 2014 behind galaxy cluster MACS J1149.5+2223 as part of Hubble’s Frontier Fields program. Astronomers spotted four separate images of the supernova in an arrangement known as an “Einstein Cross”.

    The light from the cluster has taken about five billion years to reach Earth, though the supernova exploded some 10 billion years ago. Based on early lens models, a fifth image was predicted to reappear by the end of 2015. The detection of Refsdal’s reappearance in December 2015 served as a unique opportunity for astronomers to test their models of how mass, especially dark matter, is distributed within this galaxy cluster.

    Impact on astronomy

    Many objective measures show the positive impact of Hubble data on astronomy. Over 15,000 papers based on Hubble data have been published in peer-reviewed journals, and countless more have appeared in conference proceedings. Looking at papers several years after their publication, about one-third of all astronomy papers have no citations, while only two percent of papers based on Hubble data have no citations. On average, a paper based on Hubble data receives about twice as many citations as papers based on non-Hubble data. Of the 200 papers published each year that receive the most citations, about 10% are based on Hubble data.

    Although the HST has clearly helped astronomical research, its financial cost has been large. A study on the relative astronomical benefits of different sizes of telescopes found that while papers based on HST data generate 15 times as many citations as a 4 m (13 ft) ground-based telescope such as the William Herschel Telescope, the HST costs about 100 times as much to build and maintain.

    Deciding between building ground- versus space-based telescopes is complex. Even before Hubble was launched, specialized ground-based techniques such as aperture masking interferometry had obtained higher-resolution optical and infrared images than Hubble would achieve, though restricted to targets about 108 times brighter than the faintest targets observed by Hubble. Since then, advances in “adaptive optics” have extended the high-resolution imaging capabilities of ground-based telescopes to the infrared imaging of faint objects.

    The usefulness of adaptive optics versus HST observations depends strongly on the particular details of the research questions being asked. In the visible bands, adaptive optics can correct only a relatively small field of view, whereas HST can conduct high-resolution optical imaging over a wide field. Only a small fraction of astronomical objects are accessible to high-resolution ground-based imaging; in contrast Hubble can perform high-resolution observations of any part of the night sky, and on objects that are extremely faint.

    Impact on aerospace engineering

    In addition to its scientific results, Hubble has also made significant contributions to aerospace engineering, in particular the performance of systems in low Earth orbit. These insights result from Hubble’s long lifetime on orbit, extensive instrumentation, and return of assemblies to the Earth where they can be studied in detail. In particular, Hubble has contributed to studies of the behavior of graphite composite structures in vacuum, optical contamination from residual gas and human servicing, radiation damage to electronics and sensors, and the long term behavior of multi-layer insulation. One lesson learned was that gyroscopes assembled using pressurized oxygen to deliver suspension fluid were prone to failure due to electric wire corrosion. Gyroscopes are now assembled using pressurized nitrogen. Another is that optical surfaces in LEO can have surprisingly long lifetimes; Hubble was only expected to last 15 years before the mirror became unusable, but after 14 years there was no measureable degradation. Finally, Hubble servicing missions, particularly those that serviced components not designed for in-space maintenance, have contributed towards the development of new tools and techniques for on-orbit repair.

    Archives

    All Hubble data is eventually made available via the Mikulski Archive for Space Telescopes at STScI, CADC and ESA/ESAC. Data is usually proprietary—available only to the principal investigator (PI) and astronomers designated by the PI—for twelve months after being taken. The PI can apply to the director of the STScI to extend or reduce the proprietary period in some circumstances.

    Observations made on Director’s Discretionary Time are exempt from the proprietary period, and are released to the public immediately. Calibration data such as flat fields and dark frames are also publicly available straight away. All data in the archive is in the FITS format, which is suitable for astronomical analysis but not for public use. The Hubble Heritage Project processes and releases to the public a small selection of the most striking images in JPEG and TIFF formats.

    Outreach activities

    It has always been important for the Space Telescope to capture the public’s imagination, given the considerable contribution of taxpayers to its construction and operational costs. After the difficult early years when the faulty mirror severely dented Hubble’s reputation with the public, the first servicing mission allowed its rehabilitation as the corrected optics produced numerous remarkable images.

    Several initiatives have helped to keep the public informed about Hubble activities. In the United States, outreach efforts are coordinated by the Space Telescope Science Institute (STScI) Office for Public Outreach, which was established in 2000 to ensure that U.S. taxpayers saw the benefits of their investment in the space telescope program. To that end, STScI operates the HubbleSite.org website. The Hubble Heritage Project, operating out of the STScI, provides the public with high-quality images of the most interesting and striking objects observed. The Heritage team is composed of amateur and professional astronomers, as well as people with backgrounds outside astronomy, and emphasizes the aesthetic nature of Hubble images. The Heritage Project is granted a small amount of time to observe objects which, for scientific reasons, may not have images taken at enough wavelengths to construct a full-color image.

    Since 1999, the leading Hubble outreach group in Europe has been the Hubble European Space Agency Information Centre (HEIC). This office was established at the Space Telescope European Coordinating Facility in Munich, Germany. HEIC’s mission is to fulfill HST outreach and education tasks for the European Space Agency. The work is centered on the production of news and photo releases that highlight interesting Hubble results and images. These are often European in origin, and so increase awareness of both ESA’s Hubble share (15%) and the contribution of European scientists to the observatory. ESA produces educational material, including a videocast series called Hubblecast designed to share world-class scientific news with the public.

    The Hubble Space Telescope has won two Space Achievement Awards from the Space Foundation, for its outreach activities, in 2001 and 2010.

    A replica of the Hubble Space Telescope is on the courthouse lawn in Marshfield, Missouri, the hometown of namesake Edwin P. Hubble.

    Major Instrumentation

    Hubble WFPC2 no longer in service.

    Wide Field Camera 3 [WFC3]

    Advanced Camera for Surveys [ACS]

    Cosmic Origins Spectrograph [COS]

    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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  • richardmitnick 11:04 am on July 11, 2020 Permalink | Reply
    Tags: , , , , Brown Dwarfs, , , First notice of the unusual brown dwarfs called WISE 1810 and WISE 0414,   

    From NASA/WISE and NeoWISE: “Two Bizarre Brown Dwarfs Found With Citizen Scientists’ Help” 

    NASA Wise Banner

    NASA/WISE Telescope

    From NASA/WISE and NeoWISE

    July 10, 2020

    Elizabeth Landau
    NASA Headquarters
    elandau@nasa.gov
    202-923-0167

    Karin Valentine
    Media Relations
    School of Earth and Space Exploration
    Arizona State University
    karin.valentine@asu.edu
    480-965-9345

    1
    This is an illustration of a brown dwarf. Despite their name, brown dwarfs would appear magenta or orange-red to the human eye if seen close up. Credits: Image courtesy of William Pendrill

    With the help of citizen scientists, astronomers have discovered two highly unusual brown dwarfs, balls of gas that are not massive enough to power themselves the way stars do.

    Participants in the NASA-funded Backyard Worlds: Planet 9 project helped lead scientists to these bizarre objects, using data from NASA’s Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) satellite along with all-sky observations collected between 2009 and 2011 under its previous moniker, WISE [above]. Backyard Worlds: Planet 9 is an example of “citizen science,” a collaboration between professional scientists and members of the public.

    Scientists call the newly discovered objects “the first extreme T-type subdwarfs.” They weigh about 75 times the mass of Jupiter and clock in at roughly 10 billion years old. These two objects are the most planet-like brown dwarfs yet seen among the Milky Way’s oldest population of stars.

    Astronomers hope to use these brown dwarfs to learn more about exoplanets, which are planets outside of our solar system. The same physical processes may form both planets and brown dwarfs.

    “These surprising, weird brown dwarfs resemble ancient exoplanets closely enough that they will help us understand the physics of the exoplanets,” said astrophysicist Marc Kuchner, the principal investigator of Backyard Worlds: Planet 9 and the Citizen Science Officer for NASA’s Science Mission Directorate. Kuchner is also an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

    These two special brown dwarfs have highly unusual compositions. When viewed in particular wavelengths of infrared light, they look like other brown dwarfs, but at others they do not resemble any other stars or planets that have been observed so far.

    Scientists were surprised to see they have very little iron, meaning that, like ancient stars, they have not incorporated iron from star births and deaths in their environments. A typical brown dwarf would have as much as 30 times more iron and other metals than these newly discovered objects. One of these brown dwarfs seems to have only about 3% as much iron as our Sun. Scientists expect very old exoplanets would have a low metal content, too.

    “A central question in the study of brown dwarfs and exoplanets is how much does planet formation depend on the presence of metals like iron and other elements formed by multiple earlier generations of stars,” Kuchner said. “The fact that these brown dwarfs seem to have formed with such low metal abundances suggests that maybe we should be searching harder for ancient, metal-poor exoplanets, or exoplanets orbiting ancient metal-poor stars.”

    A study in The Astrophysical Journal details these discoveries and the potential implications. Six citizen scientists are listed as co-authors of the study.

    How volunteers found these extreme brown dwarfs

    The study’s lead author, Adam Schneider of Arizona State University’s School of Earth and Space Exploration in Tempe, first noticed one of the unusual brown dwarfs, called WISE 1810, in 2016, but it was in a crowded area of the sky and was difficult to confirm.

    With the help of a tool called WiseView, created by Backyard Worlds: Planet 9 citizen scientist Dan Caselden, Schneider confirmed that the object he had seen years earlier was moving quickly, which is a good indication that an object is a nearby celestial body like a planet or brown dwarf.

    “WiseView scrolls through data like a short movie,” Schneider said, “so you can see more easily see if something is moving or not.”

    The second unusual brown dwarf, WISE 0414, was discovered by a group of citizen scientists including Backyard Worlds participants Paul Beaulieu, Sam Goodman, William Pendrill, Austin Rothermich, and Arttu Sainio.

    The citizen scientists who found WISE 0414 combed through hundreds of images taken by WISE looking for moving objects, which are best detected with the human eye.

    “The discovery of these two brown dwarfs shows that science enthusiasts can contribute to the scientific process,” Schneider said. “Through Backyard Worlds, thousands of people can work together to find unusual objects in the solar neighborhood.”

    Astronomers followed up to determine their physical properties and confirm that they are indeed brown dwarfs. The discovery of these two unusual brown dwarfs suggests astronomers may be able to find more of these objects in the future.

    See the full article here .

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    NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Wide-field Infrared Survey Explorer for NASA’s Science Mission Directorate, Washington. The mission’s principal investigator, Edward L. (Ned) Wright, is at UCLA. The mission was competitively selected in 2002 under NASA’s Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp, Boulder, Colo. Science operations and data processing will take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

    The mission’s education and public outreach office is based at the University of California, Berkeley.

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  • richardmitnick 12:06 pm on February 27, 2018 Permalink | Reply
    Tags: 2MASS J13243553+6358281, , , , Brown Dwarfs, ,   

    From Carnegie Institution for Science: “When do aging brown dwarfs sweep the clouds away? “ 

    Carnegie Institution for Science
    Carnegie Institution for Science

    February 26, 2018
    No writer credit

    1
    An artist’s conception of a brown dwarf. Image is courtesy of NASA/JPL, slightly modified by Jonathan Gagné.

    Brown dwarfs, the larger cousins of giant planets, undergo atmospheric changes from cloudy to cloudless as they age and cool. A team of astronomers led by Carnegie’s Jonathan Gagné measured for the first time the temperature at which this shift happens in young brown dwarfs. Their findings, published by The Astrophysical Journal Letters, may help them better understand how gas giant planets like our own Solar System’s Jupiter evolved.

    Brown dwarfs are too small to sustain the hydrogen fusion process that fuels stars and allows them to remain hot and bright for a long time. After formation, brown dwarfs slowly cool down and contract over time—at some point shifting from heavily cloud covered to having completely clear skies.

    Because they are freely floating in space, the atmospheric properties of brown dwarfs are much easier to study than the atmospheres of exoplanets, where the light of a central star can be completely overwhelming.

    In this paper, Gagné and his colleagues—Katelyn Allers of Bucknell University; Christopher Theissen of University of California San Diego; Jacqueline Faherty and Daniella Bardalez Gagliuffi of the American Museum of Natural History, and Etienne Artigau of Institute for Research on Exoplanets, Université de Montréal—focused on an unusually red brown dwarf called 2MASS J13243553+6358281, which they were able to determine is one of the nearest known planetary mass objects to our Solar System.

    The redness of this object had previously been suggested to indicate that it was actually a binary system, but the research team’s findings indicate that it is a single free floating planetary mass object.

    They confirmed that it is part of a group of roughly 80 stars of similar ages and compositions drifting together through space, called the AB Doradus moving group, which revealed that it is about 150 million years old.

    By knowing the object’s age and measuring its luminosity and distance, the team could determine its likely radius, mass, and, most-importantly its temperature.

    They could then compare its temperature to that of another previously studied brown dwarf in the same moving group—one that was still cloudy while 2MASS J1324+6358 was already cloudless. This allowed them to figure out the temperature at which the cloudy to cloudless transition happens.

    “We were able to constrain the point in the cool-down process at which brown dwarfs like J1324transition from cloudy to cloud-free,” explained Gagné

    The shift occurs about 1,150 degrees kelvin, or 1,600 degrees Fahrenheit, for planetary-mass objects that are 150 million years old like 2MASS J1324+6358 and other members of the AB Doradus moving group.

    “Because brown dwarfs like this one are so analogous to gas giant planets, this information could help us understand some of the evolutionary processes that occurred right here in our own Solar System’s history,” Gagné added.

    This research made use of data products from the Two Micron All Sky Survey (2MASS), which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center (IPAC)/California Institute of Technology (Caltech), funded by the National Aeronautics and Space Administration (NASA) and the National Science Foundation; and data products from the Wide-field Infrared Survey Explorer (WISE), which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory (JPL)/Caltech, funded by NASA. Based on observations obtained at the Gemini Observatory (science program number GN2017B-FT-21) acquired through the Gemini Observatory Archive, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnologia e Innovacion Productiva (Argentina), and Ministerio da Ciencia, Tecnologia e Inova¸cao (Brazil).


    Caltech 2MASS Telescopes, a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center (IPAC) at Caltech, at the Whipple Observatory on Mt. Hopkins south of Tucson, AZ, and at the Cerro Tololo Inter-American Observatory near La Serena, Chile.

    NASA/WISE Telescope

    See the full article here .

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    Carnegie Institution of Washington Bldg

    Andrew Carnegie established a unique organization dedicated to scientific discovery “to encourage, in the broadest and most liberal manner, investigation, research, and discovery and the application of knowledge to the improvement of mankind…” The philosophy was and is to devote the institution’s resources to “exceptional” individuals so that they can explore the most intriguing scientific questions in an atmosphere of complete freedom. Carnegie and his trustees realized that flexibility and freedom were essential to the institution’s success and that tradition is the foundation of the institution today as it supports research in the Earth, space, and life sciences.

    6.5 meter Magellan Telescopes located at Carnegie’s Las Campanas Observatory, Chile.
    6.5 meter Magellan Telescopes located at Carnegie’s Las Campanas Observatory, Chile

     
  • richardmitnick 10:01 am on January 25, 2018 Permalink | Reply
    Tags: An upper boundary on the masses of planets, , , , Brown Dwarfs, , , Johns Hopkins Scientist Proposes New Definition of a Planet   

    From Hopkins: “Johns Hopkins Scientist Proposes New Definition of a Planet” 

    Johns Hopkins
    Johns Hopkins University

    January 22, 2018
    Phil Sneiderman
    prs@jhu.edu
    Office: 443-997-9907
    Cell: 410-299-7462

    1
    Johns Hopkins astrophysicist Kevin Schlaufman has proposed a new definition of a planet. Photo: Johns Hopkins University.

    Pluto hogs the spotlight in the continuing scientific debate over what is and what is not a planet, but a less conspicuous argument rages on about the planetary status of massive objects outside our solar system. The dispute is not just about semantics, as it is closely related to how giant planets like Jupiter form.

    Johns Hopkins University astrophysicist Kevin Schlaufman aims to settle the dispute.

    In a paper just published in The Astrophysical Journal, Schlaufman has set the upper boundary of planet mass between four and 10 times the mass of the planet Jupiter.

    Schlaufman, an assistant professor in the university’s Department of Physics & Astronomy, says setting a limit is possible now mainly due to improvements in the technology and techniques of astronomical observation. The advancements have made it possible to discover many more planetary systems outside our solar system and therefore possible to see robust patterns that lead to new revelations.

    “While we think we know how planets form in a big picture sense, there’s still a lot of detail we need to fill in,” Schlaufman said. “An upper boundary on the masses of planets is one of the most prominent details that was missing.”

    The conclusions in the new paper are based on observations of 146 solar systems, systems, Schlaufman said, is the fact that almost all the data he used was measured in a uniform way. The data are more consistent from one solar system to the next, and so more reliable.

    Defining a planet, distinguishing it from other celestial objects, is a bit like narrowing down a list of criminal suspects. It’s one thing to know you’re looking for someone who is taller than 5-foot-8, it’s another to know your suspect is between 5-foot-8 and 5-foot-10.

    In this instance, investigators want to distinguish between two suspects: a giant planet and a celestial object called a brown dwarf. Brown dwarfs are more massive than planets, but less massive than the smallest stars. They are thought to form as stars do.

    For decades brown dwarfs have posed a problem for scientists: how to distinguish low-mass brown dwarfs from especially massive planets? Mass alone isn’t enough to tell the difference bzween the two, Schlaufman said. Some other property was needed to draw the line.

    In Schlaufman’s new argument, the missing property is the chemical makeup of a solar system’s own sun. He says you can know your suspect, a planet, not just by his size, but also by the company he keeps. Giant planets such as Jupiter are almost always found orbiting stars that have more iron than our sun. Brown dwarfs are not so discriminating.

    That’s where his argument engages the idea of planet formation. Planets like Jupiter are formed from the bottom-up by first building-up a rocky core that is subsequently enshrouded in a massive gaseous envelope. It stands to reason that they would be found near stars heavy with elements that make rocks, as those elements provide the seed material for planet formation. Not so with brown dwarfs.

    Brown dwarfs and stars form from the top-down as clouds of gas collapse under their own weight.

    Schlaufman’s idea was to find the mass at which point objects stop caring about the composition of the star they orbit. He found that objects more massive than about 10 times the mass of Jupiter do not prefer stars with lots of elements that make rocks and therefore are unlikely to form like planets.

    For that reason, and while it’s possible that new data could change things, he has proposed that objects in excess of 10 Jupiter mass should be considered brown dwarfs, not planets.

    Artist’s concept of a Brown dwarf [not quite a] star. NASA/JPL-Caltech

    See the full article here .

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    Johns Hopkins Campus

    The Johns Hopkins University opened in 1876, with the inauguration of its first president, Daniel Coit Gilman. “What are we aiming at?” Gilman asked in his installation address. “The encouragement of research … and the advancement of individual scholars, who by their excellence will advance the sciences they pursue, and the society where they dwell.”

    The mission laid out by Gilman remains the university’s mission today, summed up in a simple but powerful restatement of Gilman’s own words: “Knowledge for the world.”

    What Gilman created was a research university, dedicated to advancing both students’ knowledge and the state of human knowledge through research and scholarship. Gilman believed that teaching and research are interdependent, that success in one depends on success in the other. A modern university, he believed, must do both well. The realization of Gilman’s philosophy at Johns Hopkins, and at other institutions that later attracted Johns Hopkins-trained scholars, revolutionized higher education in America, leading to the research university system as it exists today.

     
  • richardmitnick 12:40 pm on January 4, 2018 Permalink | Reply
    Tags: , , , Brown Dwarfs, Caltech Palomar 1.5 meter 60 inch telescope, , ,   

    From Hubble: “Astronomers Announce First Clear Evidence of a Brown Dwarf” 1995 but Important 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope

    NASA/ESA Hubble Telescope

    Nov 29, 1995 [Just found this. It is important.]

    Don Savage
    NASA Headquarters, Washington, DC
    202-358-1547

    Jim Sahli
    Goddard Space Flight Center, Greenbelt, MD
    301-286-0697

    Ray Villard
    Space Telescope Science Institute, Baltimore, MD
    410-338-4514

    1
    S. Kulkarni (Caltech), D.Golimowski (JHU) and NASA

    Astronomers have made the first unambiguous detection and image of an elusive type of object known as a brown dwarf.

    The evidence consists of an image from the 60-inch observatory on Mt. Palomar, a spectrum from the 200-inch Hale telescope on Mt. Palomar and a confirmatory image from NASA’s Hubble Space Telescope. The collaborative effort involved astronomers at the California Institute of Technology, Pasadena, CA, and the Johns Hopkins University, Baltimore, MD.


    Caltech Palomar 1.5 meter 60 inch telescope, Altitude 1,712 m (5,617 ft)


    Caltech Palomar 200 inch Hale Telescope, at Mt Wilson, CA, USA, Altitude 1,712 m (5,617 ft)

    The brown dwarf, called Gliese 229B (GL229B), is a small companion to the cool red star Gliese 229, located 19 light-years from Earth in the constellation Lepus.

    3
    Gliese 229. SolStation.com

    Estimated to be 20 to 50 times the mass of Jupiter, GL229B is too massive and hot to be classified as a planet as we know it, but too small and cool to shine like a star. At least 100,000 times dimmer than Earth’s Sun, the brown dwarf is the faintest object ever seen orbiting another star.

    “This is the first time we have ever observed an object beyond our solar system which possesses a spectrum that is astonishingly just like that of a gas giant planet,” said Shrinivas Kulkarni, a member of the team from Caltech.

    Kulkarni added, however, that “it looks like Jupiter, but that’s what you’d expect for a brown dwarf.” The infrared spectroscopic observations of GL229B, made with the 200-inch Hale telescope at Palomar, show that the dwarf has the spectral fingerprint of the planet Jupiter – an abundance of methane. Methane is not seen in ordinary stars, but it is present in Jupiter and other giant gaseous planets in our solar system.

    The Hubble data obtained and analyzed so far already show the object is far dimmer, cooler (no more than 1,300 degrees Fahrenheit) and less massive than previously reported brown dwarf candidates, which are all near the theoretical limit (eight percent the mass of our Sun) where a star has enough mass to sustain nuclear fusion.

    Brown dwarfs are a mysterious class of long-sought object that forms the same way stars do, that is, by condensing out of a cloud of hydrogen gas. However, they do not accumulate enough mass to generate the high temperatures needed to sustain nuclear fusion at their core, which is the mechanism that makes stars shine. Instead brown dwarfs shine the same way that gas giant planets like Jupiter radiate energy, that is, through gravitational contraction. In fact, the chemical composition of GL229B’s atmosphere looks remarkably like that of Jupiter.

    The discovery is an important first step in the search for planetary systems beyond the Solar System because it will help astronomers distinguish between massive Jupiter-like planets and brown dwarfs orbiting other stars. Advances in ground- and space-based astronomy are allowing astronomers to further probe the “twilight zone” between larger planets and small stars as they search for substellar objects, and eventually, planetary systems.

    Caltech astronomers Kulkarni, Tadashi Nakajima, Keith Matthews, and Ben Oppenheimer, and Johns Hopkins scientists Sam Durrance and David Golimowski first discovered the object in October 1994. Follow-up observations a year later were needed to confirm it is actually a companion to Gliese 229. The discovery was made with a 60-inch reflecting telescope at Palomar Observatory in southern California, using an image-sharpening device called the Adaptive Optics Coronagraph, designed and built at the Johns Hopkins University.

    The same scientists teamed up with Chris Burrows of the Space Telescope Science Institute to use Hubble’s Wide Field Planetary Camera-2 for follow-up observations on November 17.

    NASA/Hubble WFPC2. No longer in service.

    Another Hubble observation six months from now will yield an exact distance to GL229B.

    The astronomers suspect that the brown dwarf developed during the normal star-formation process as one of two members of a binary system. “All our observations are consistent with brown dwarf theory,” Durrance said. However, the astronomers say they cannot yet fully rule out the possibility that the object formed out of dust and gas in a circumstellar disk as a “super-planet.”

    Astronomers say the difference between planets and brown dwarfs is based on how they formed. Planets in the Solar System are believed to have formed out of a primeval disk of dust around the newborn Sun because all the planets’ orbits are nearly circular and lie almost in the same plane. Brown dwarfs, like full-fledged stars, would have fragmented and gravitationally collapsed out of a large cloud of hydrogen but were not massive enough to sustain fusion reactions at their cores.

    The orbit of GL229B could eventually provide clues to its origin. If the orbit is nearly circular then it may have formed out of a dust disk, where viscous forces in the dense disk would keep objects at about the same distance from their parent star. If the dwarf formed as a binary companion, its orbit probably would be far more elliptical, as seen on most binary stars. The initial Hubble observations will begin providing valuable data for eventually calculating the brown dwarf’s orbit. However, the orbital motion is so slow, it will take many decades of telescopic observations before a true orbit can be calculated. GL229B is at least four billion miles from its companion star, which is roughly the separation between the planet Pluto and our Sun.

    Astronomers have been trying to detect brown dwarfs for three decades. Their lack of success is partly due to the fact that as brown dwarfs age they become cooler, fainter, and more difficult to see. An important strategy used by the researchers to search for brown dwarfs was to view stars no older than a billion years. Caltech’s Nakajima reasoned that, although brown dwarfs of that age would be much fainter than any known star, they would still be bright enough to be spotted.

    “Another reason brown dwarfs were not detected years ago is that imaging technology really wasn’t up to the task,” Golimowski said. With the advent of sophisticated light sensors and adaptive optics, astronomers now have the powerful tools they need to resolve smaller and dimmer objects near stars.

    Hubble was used to look for the presence of other companion objects as bright as the brown dwarf which might be as close to the star as one billion miles. No additional objects were found, though it doesn’t rule out the possibility of Jupiter-sized or smaller planets around the star, said the researchers.

    The Palomar results will also appear in the November 30 issue of the journal Nature and the December 1 issue of the journal Science.

    A GALAXY DWELLER’S GUIDE TO PLANETS, STARS, AND DWARFS

    “Twinkle little star, how I wonder what you are . . .”

    Today, you might just as easily find astronomers humming this nursery rhyme as well as children. Rapid advances in telescope technology – adaptive optics, space observatories, interferometry, image processing techniques – are allowing astronomers to see ever fainter and smaller companions to normal stars. As telescopic capabilities sharpen, conventional definitions for planets and stars may seem to be getting blurry. In the search for other planetary systems, astronomers are turning up objects that straddle the dim twilight zone between planets and stars, and others that seem to contradict conventional wisdom, such as a planetary system accompanying a burned-out compacted star called a neutron star.

    Stars

    Stars are large gaseous bodies that generate energy through nuclear fusion processes at their cores –where temperatures and pressures are high enough for hydrogen nuclei to collide and fuse into helium nuclei, converting matter to energy in the process. Stars are born out of clouds of hydrogen, that collapse under gravity to form dense knots of gas. This collapse continues until enough pressure builds up to heat the gas and trigger nuclear fusion. The energy released by this “fusion-engine” halts the collapse, and the star is in equilibrium.

    A star’s brightness, temperature, color and lifetime are all determined by its initial mass. Our Sun is a typical middle-aged star halfway through its ten billion-year life. Stars can be 100 times more massive than our Sun, or less that 1/10 its mass. A Hubble Space Telescope search for dim stars suggests that most stars in the galaxy are about 1/5 the mass of our Sun.

    Following a fiery birth, stars lead tranquil lives as inhabitants of the galaxy. Late in a star’s life, fireworks can begin anew as changes in the core heat the stars further, eject its outer layers, and cause it to pulsate. All stars eventually burn out. Most collapse to white dwarf stars – dim planet-sized objects that are extraordinarily dense because they retain most of their initial mass. Extremely massive stars undergo catastrophic core collapse and explode as supernovae – the most energetic events in the universe. Black holes and neutron stars – ultra dense stellar remnants with intense gravitational fields – can be created in supernova blasts.

    At least half of the stars in the galaxy have companion stars. These binary star systems can undergo complicated evolutionary changes as one star ages more rapidly than the companion and dies out. If the two stars are close enough together, gas will flow between them and this can trigger nova outbursts. Supernovae and novae are key forces in a grand cycle of stellar rebirth and renewal. Heavier elements cooked up in the fusion furnaces of stars are ejected back into space, serving as raw material for building new generations of stars and planets.

    Planets

    Though the universe contains billions upon billions of stars, until recently only nine planets were known – those of our solar system. The Solar System provides a fundamental model for what we might expect to find around other stars, but it’s difficult to form generalities from just one example. It may turn out that nature is more varied and imaginative when it comes to building and distributing planets throughout the Galaxy.

    In it simplest definition, a planet is a nonluminous body that orbits a star, and is typically a small fraction of the parent star’s mass. Planets form out of a disk of dust and gas that encircles a newborn star. These embryonic disks have been observed around young stars, both in infrared and visible light. The planets’ orbits in our solar system trace out the skeleton of just such a disk that encircled the newborn Sun.

    Planets agglomerate from the collision of dust particles in the disk, and then snowball in size to solid bodies that continue gobbling up debris like cosmic Pac-Men. In the case of our solar system this led to eight major bodies, thousands to tens of thousands of miles across. (The ninth planet, Pluto, is probably a survivor of an early subclass of solar system inhabitants called icy dwarfs). A planet’s mass and composition are determined by where it formed in the disk. In the case of our solar system the more massive planets are found far from the Sun, though not too far where material didn’t have time to agglomerate (because orbital periods were so slow that chances for collisions were minimal).

    Unlike asteroids which are cold chunks of solar system debris, a planet must be massive enough to have at least once had a molten core that differentiated the planet’s interior. This is a process where heavier elements sank to the center and lighter elements float to the surface. According to this idea, planets should have dense rocky/metallic cores. Depending how far they formed from their parent star, they may retain a dense mantle of primordial hydrogen and helium. In the case of our solar system this establishes two families of planets: the inner rocky or terrestrial planets such as Earth and Mars, which have solid surfaces, and the outer gas giant planets Jupiter and Saturn that are mostly gaseous and liquid. Massive planet like Jupiter are still gravitationally contracting and shine in infrared light.

    Ironically, the first bonafide planetary system ever detected beyond our Sun exists around a neutron star – a collapsed stellar core left over from the star’s self-detonation as a supernova. Resembling our inner solar system in terms of size and distribution, these three planets orbiting the crushed star probably formed after the star exploded. Apparently a disk must have formed after the stellar death, from which the planets agglomerated. Other suspected extrasolar planets also seem to defy conventional wisdom. An object orbiting the star 51 Pegasus may have the mass of Jupiter, but is 20 times closer to the star than Earth is from the Sun.

    Brown Dwarfs

    Brown dwarfs are the galaxy’s underachievers. They never quite made it as stars. Like stars, brown dwarfs collapse out of a cloud of hydrogen. Like a planet they are too small to shine by nuclear fusion, and radiate energy only through gravitational contraction. (More massive brown dwarfs might have initiated fusion, but could not sustain it.) Their predicted masses range from several times the mass of Jupiter to a few percent the mass of our Sun. Spectroscopically, the cool dwarfs may resemble gas giant planets in terms of chemical composition.

    A Color-Guide to Dwarfs

    The different type of so-called “dwarfs” in the Galaxy would even befuddle the storybook character, Snow White:

    • White dwarfs – Burned-out stars that no longer shine through nuclear fusion, and have collapsed to Earth-sized objects. Ironically, their surface temperature rises as they collapse and so the star is white-hot.
    • Yellow dwarfs – Normal stars with our Sun’s temperature and mass.
    • Red dwarfs – Stars that are small, cooler and hence, dimmer than our Sun. The cooler a star the redder it is, just as a dying ember fades from yellow-orange to cherry-red.
    • Brown dwarfs – Substellar objects that have formed like a star, but are not massive enough to sustain nuclear fusion processes.
    • Black dwarfs – White dwarfs that cool to nearly absolute zero. The universe isn’t old enough yet for black dwarfs to exist.

    See the full article here .

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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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  • richardmitnick 12:10 pm on January 4, 2018 Permalink | Reply
    Tags: , , , , Brown Dwarfs, , CSA Webb Slitless Spectrograph (NIRISS), NASA Webb Near Infrared Imager NIRCam,   

    From NASA Webb: “NASA’s Webb Telescope to Investigate Mysterious Brown Dwarfs” 

    NASA Webb Header

    NASA Webb Telescope

    James Webb Space Telescope

    Jan. 4, 2018
    Leah Ramsay
    Space Telescope Science Institute, Baltimore, Md.

    Twinkle, twinkle, little star, how I wonder what you are. Astronomers are hopeful that the powerful infrared capability of NASA’s James Webb Space Telescope will resolve a puzzle as fundamental as stargazing itself — what IS that dim light in the sky? Brown dwarfs muddy a clear distinction between stars and planets, throwing established understanding of those bodies, and theories of their formation, into question.

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    Stellar cluster NGC 1333 is home to a large number of brown dwarfs. Astronomers will use Webb’s powerful infrared instruments to learn more about these dim cousins to the cluster’s bright newborn stars. Credits: NASA/CXC/JPL

    Several research teams will use Webb to explore the mysterious nature of brown dwarfs, looking for insight into both star formation and exoplanet atmospheres, and the hazy territory in-between where the brown dwarf itself exists. Previous work with Hubble, Spitzer, and ALMA have shown that brown dwarfs can be up to 70 times more massive than gas giants like Jupiter, yet they do not have enough mass for their cores to burn nuclear fuel and radiate starlight.

    NASA/ESA Hubble Telescope

    NASA/Spitzer Infrared Telescope

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    Though brown dwarfs were theorized in the 1960s and confirmed in 1995, there is not an accepted explanation of how they form: like a star, by the contraction of gas, or like a planet, by the accretion of material in a protoplanetary disk? Some have a companion relationship with a star, while others drift alone in space.

    At the Université de Montréal, Étienne Artigau leads a team that will use Webb to study a specific brown dwarf, labeled SIMP0136.

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    SIMP0136+0933. http://www.exoplanetkyoto.org

    It is a low-mass, young, isolated brown dwarf — one of the closest to our Sun — all of which make it fascinating for study, as it has many features of a planet without being too close to the blinding light of a star. SIMP0136 was the object of a past scientific breakthrough by Artigau and his team, when they found evidence suggesting it has a cloudy atmosphere. He and his colleagues will use Webb’s spectroscopic instruments to learn more about the chemical elements and compounds in those clouds.

    “Very accurate spectroscopic measurements are challenging to obtain from the ground in the infrared due to variable absorption in our own atmosphere, hence the need for space-based infrared observation. Also, Webb allows us to probe features, such as water absorption, that are inaccessible from the ground at this level of precision,” Artigau explains.

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    Artist’s conception of a brown dwarf, featuring the cloudy atmosphere of a planet and the residual light of an almost-star. Credits: NASA/ESA/JPL

    These observations could lay groundwork for future exoplanet exploration with Webb, including which worlds could support life. Webb’s infrared instruments will be capable of detecting the types of molecules in the atmospheres of exoplanets by seeing which elements are absorbing light as the planet passes in front of its star, a scientific technique known as transit spectroscopy.

    “The brown dwarf SIMP0136 has the same temperature as various planets that will be observed in transit spectroscopy with Webb, and clouds are known to affect this type of measurement; our observations will help us better understand cloud decks in brown dwarfs and planet atmospheres in general,” Artigau says.

    The search for low-mass, isolated brown dwarfs was one of the early science goals put forward for the Webb telescope in the 1990s, says astronomer Aleks Scholz of the University of St. Andrews. Brown dwarfs have a lower mass than stars and do not “shine” but merely emit the dim afterglow of their birth, and so they are best seen in infrared light, which is why Webb will be such a valuable tool in this research.

    Scholz, who also leads the Substellar Objects in Nearby Young Clusters (SONYC) project, will use Webb’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) to study NGC 1333 in the constellation of Perseus. NGC 1333 is a stellar nursery that has also been found to harbor an unusually high number of brown dwarfs, some of them at the very low end of the mass range for such objects – in other words, not much heavier than Jupiter.

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    NASA Webb Near Infrared Imager NIRCam

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    CSA Webb Slitless Spectrograph (NIRISS)

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    Dusty NGC 1333 is seen as a reflection nebula in visible light images, sporting bluish hues characteristic of starlight reflected by dust. But at longer infrared wavelengths, the interstellar dust itself glows – shown in red in this false-color Spitzer Space Telescope image. The penetrating infrared view also shows youthful stars that would otherwise still be obscured by the dusty clouds which formed them. Notably, greenish streaks and splotches that seem to litter the region trace the glow of cosmic jets blasting away from emerging young stellar objects as the jets plow into the cold cloud material. In all, the chaotic scene likely resembles one in which our own Sun formed over 4.5 billion years ago. NGC 1333 is a mere 1,000 light-years distant in the constellation Perseus.

    “In more than a decade of searching, our team has found it is very difficult to locate brown dwarfs that are less than five Jupiter-masses – the mass where star and planet formation overlap. That is a job for the Webb telescope,” Scholz says. “It has been a long wait for Webb, but we are very excited to get an opportunity to break new ground and potentially discover an entirely new type of planets, unbound, roaming the Galaxy like stars.”

    Both of the projects led by Scholz and Artigau are making use of Guaranteed Time Observations (GTOs), observing time on the telescope that is granted to astronomers who have worked for years to prepare Webb’s scientific operations.

    The James Webb Space Telescope, the scientific complement to NASA’s Hubble Space Telescope, will be the premier space observatory of the next decade. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

    For more information about the Webb telescope, visit http://www.nasa.gov/webb or http://www.webbtelescope.org

    See the full article here .

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    The James Webb Space Telescope will be a large infrared telescope with a 6.5-meter primary mirror. Launch is planned for later in the decade.

    Webb telescope will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.

    Webb telescope was formerly known as the “Next Generation Space Telescope” (NGST); it was renamed in Sept. 2002 after a former NASA administrator, James Webb.

    Webb is an international collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center is managing the development effort. The main industrial partner is Northrop Grumman; the Space Telescope Science Institute will operate Webb after launch.

    Several innovative technologies have been developed for Webb. These include a folding, segmented primary mirror, adjusted to shape after launch; ultra-lightweight beryllium optics; detectors able to record extremely weak signals, microshutters that enable programmable object selection for the spectrograph; and a cryocooler for cooling the mid-IR detectors to 7K.

    There will be four science instruments on Webb: the Near InfraRed Camera (NIRCam), the Near InfraRed Spectrograph (NIRspec), the Mid-InfraRed Instrument (MIRI), and the Fine Guidance Sensor/ Near InfraRed Imager and Slitless Spectrograph (FGS-NIRISS). Webb’s instruments will be designed to work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range. It will be sensitive to light from 0.6 to 28 micrometers in wavelength.
    Webb has four main science themes: The End of the Dark Ages: First Light and Reionization, The Assembly of Galaxies, The Birth of Stars and Protoplanetary Systems, and Planetary Systems and the Origins of Life.

    Launch is scheduled for later in the decade on an Ariane 5 rocket. The launch will be from Arianespace’s ELA-3 launch complex at European Spaceport located near Kourou, French Guiana. Webb will be located at the second Lagrange point, about a million miles from the Earth.

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    Canadian Space Agency

     
  • richardmitnick 9:08 pm on December 1, 2017 Permalink | Reply
    Tags: , , , Brown Dwarfs, , , Koraljka Muzic   

    From ESOblog: “Brown Dwarf Formation Hints at Billions of New Neighbours” 

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    ESOblog

    1 December 2017

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    Is it a star? Is it a planet? No, it’s a brown dwarf! More massive than Jupiter but smaller than the Sun, these fascinating astronomical objects are difficult to observe due to their dim nature, but studying them can tell us a lot about our Universe. In this blog post, astronomer and brown dwarf expert Koraljka Muzic discusses her latest research, which led her to discover something surprising about how brown dwarfs form.

    Q: Firstly, what exactly is a brown dwarf, and why did you want to study them in this context?

    A: For a long time, people have known about two well-separated classes of objects — stars and planets. Brown dwarfs are kind of a missing link between them: in terms of mass, they are somewhere between stars and planets. The transition from a brown dwarf to a star happens at 0.075 solar masses (around 80 times the mass of Jupiter), but setting a boundary between brown dwarfs and planets isn’t so straightforward. The smallest brown dwarfs discovered so far are about five times as massive as Jupiter, similar to some giant exoplanets. But these brown dwarfs don’t orbit any star; we call them free-floating planetary-mass objects.

    For us, the big question is: are brown dwarfs formed like stars or like planets?

    While most of the evidence today points to a star-like formation scenario for more massive brown dwarfs, we’re still questioning how low-mass brown dwarfs form; they could be formed in a similar way as giant planets.

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    Artist’s impression of the relative sizes of brown dwarfs compared to stars and gas giant planets. Using Jupiter as a comparison, the brown dwarf is 10 times more massive, the low-mass star is 100 times more massive, and the Sun is approximately 1000 times more massive.
    Credit: Carnegie Institution for Science

    Q. The existence of brown dwarfs was only confirmed about 20 years ago. How far has our knowledge of them developed since that discovery?

    A: Quite a bit! Brown dwarfs have existed in theory since the 1960s and were observed for the first time in the 1990s. Since then, we’ve discovered a few thousand of them with progressively cooler effective temperatures, leading to the definition of new stellar types.

    But observing brown dwarfs is challenging because they’re very faint and very cool, which means we’re always pushing the limits of instrument sensitivity. Our progress is strongly linked to technological development — firstly, we saw this with the arrival of infrared instrumentation that could study cool, young objects surrounded by dust. Nowadays, technological progress mostly involves building bigger mirrors on the ground and in space to detect fainter objects that are even less massive and more distant. The Milky Way contains billions of brown dwarfs, so there’s still a long way to go!

    Q: What’s our current understanding of how brown dwarfs form?

    A: We think that massive brown dwarfs are formed like stars, through the gravitational collapse of molecular clouds. This collapse causes the temperature at the cloud’s core to soar, and at a few million degrees, hydrogen starts fusing into helium — a star has been born! But if the object is not massive enough, the collapse will stop before it reaches the hydrogen fusion temperature, and the result is a brown dwarf.

    The key point for our research is that after gravitational collapse stops, the brown dwarf keeps cooling down and becoming fainter and fainter — so we want to study them while they’re young and relatively bright. This is one of the reasons we looked for brown dwarfs in a star forming region: the young cluster RCW 38.

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    The objects that astronomers call brown dwarfs sit somewhere between the definition of a planet and a star. They are balls of gas with more mass than a planet, but not enough mass to sustain stable hydrogen fusion like a star. Because they hardly emit any visible light, they were only first discovered in 1995 and up until today the majority of known brown dwarfs are within 1500 light-years of us.

    Now, astronomers using the NACO adaptive optics infrared camera on ESO’s Very Large Telescope have observed the star cluster RCW 38 in the constellation Vela (the Sail), about 5500 light-years away. This Picture of the Week shows the central part of RCW 38; the inserts on the sides show a subset of the brown dwarf candidates detected within the cluster.

    The scientists found half as many brown dwarfs as stars in the cluster. From these results and from studying other star clusters, the astronomers estimate that the Milky Way contains at least between 25 to 100 billion brown dwarfs. RCW 38 probably contains even more less massive, fainter brown dwarfs, which are beyond the detection limits of this image — so this new estimate could actually be a significant underestimation. Further surveys will reveal the true number of brown dwarfs lurking in the Milky Way.

    Credit: ESO/Koraljka Muzic (University of Lisbon), Aleks Scholz (University of St Andrews), Rainer Schoedel (Instituto de Astrofísica de Andalucía), Vincent Geers (UKATC), Ray Jayawardhana (York University), Joana Ascenso (University of Porto & University of Lisbon) & Lucas Cieza (University Diego Portales)

    Q: What were the other reasons for choosing to observe RCW 38?

    A: Several theories of brown dwarf formation predict that in places where lots of stars are packed in close together, more brown dwarfs form relative to stars. Brown dwarfs can also form close to massive stars — these stars blast a growing pre-stellar core with ionising radiation, evaporating their outer layers and leaving a small fragment behind: a brown dwarf. So in our survey SONYC (Substellar Objects in Nearby Young Clusters), we extensively studied brown dwarfs in several nearby star-forming regions in the near-infrared. These are excellent spots for studying young brown dwarfs, but overall they’re not very dense and they contain very few massive stars.

    We wanted to observe a cluster that’s significantly different to these regions in order to compare different kinds of environments. That’s how we decided on RCW 38 — it’s probably the most massive and densest cluster containing brown dwarfs detectable with our current technology. We went on to investigate RCW 38 using NACO on ESO’s Very Large Telescope.

    ESO/NACO

    ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    Q: What did you find out? Were your results surprising?

    A: We found that RCW 38 forms approximately one brown dwarf for every two newborn stars, which is very similar to what we found in less dense clusters — for example, in NGC 1333. NGC 1333 is about 10 times less dense than RCW 38 but the number of brown dwarfs formed compared to stars seems to be the same as in RCW 38. This allows us to estimate that the Milky Way contains at least between 25 to 100 billion brown dwarfs! And it’s likely that RCW 38 contains even more less massive, fainter brown dwarfs that we couldn’t spot.

    The result was unexpected because it didn’t match theoretical predictions, and was especially surprising because previous observations hinted that the stellar density should affect the number ratio of brown dwarfs to stars…but in this case, it didn’t!

    Q: What excites you most about your area of research?

    A: I love thinking about the next steps we could take to give us new information about the properties of brown dwarfs, or details about their formation. I get really excited when a new opportunity arises to do something that we simply couldn’t have done before, like use a new instrument or a state-of-the-art technique. Recently, there was a call for science research proposals for the NASA/ESA/CSA James Webb Space Telescope (JWST). Thinking that in just a few years we might be able to use this fantastic new instrument to observe Jupiter-like free-floating objects in young clusters is just incredibly exciting!

    Q: What are the next big questions in this area of astronomy?

    A: One of the big questions I’m particularly interested in is how low a brown dwarf’s mass can be — is there a limit at which brown dwarfs stop forming? This could tell us more about how these objects are born. The lowest mass brown dwarfs we observed in young clusters are only about five times more massive than Jupiter, but to see lower masses we’ll have to wait for the next generation telescopes such as the JWST and ESO’s Extremely Large Telescope. Another big question is whether brown dwarfs can host planetary systems. Observations at longer wavelengths, in mid-infrared and submillimetre, reveal that they can be surrounded by discs. The lowest mass object observed to host a disc is OTS44, a young brown dwarf of only about 10–15 Jupiter masses. And, fun fact: when the VLT took the first image of an exoplanet in 2004, it was a planet that was orbiting a brown dwarf!

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    The reflection nebula NGC 1333, located in the constellation of Perseus.
    Credit: X-ray: NASA/CXC/SAO/S.Wolk et al; Optical: DSS & NOAO/AURA/NSF; Infrared: NASA/JPL-Caltech

    NASA/Chandra Telescope

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    NASA/Spitzer Infrared Telescope

    Q: To study RCW 38, you used the Very Large Telescope at ESO’s Paranal Observatory in Chile. What was it like to work at Paranal?

    A: I worked at Paranal for three years as an ESO Fellow. Observatories in general are wonderful places, and although it can be pretty tiring, I love spending time at them because you glimpse the many complexities that lie behind astronomical observations. Building and running an observatory is an enormous effort, involving a huge number of people with different skills and expertise. It’s like a giant mechanical clock where everything has to work in perfect order to ensure astronomers around the world get the best data possible.

    Science paper:
    The low-mass content of the massive young star cluster RCW38 Koraljka Muzic, Rainer Schodel, Alexander Scholz, Vincent C. Geers, Ray Jayawardhana, Joana Ascenso and Lucas A. Cieza

    See the full article here .

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  • richardmitnick 3:07 pm on August 17, 2017 Permalink | Reply
    Tags: , , , Brown Dwarfs, ,   

    From JPL: “Scientists Improve Brown Dwarf Weather Forecasts” 

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    JPL-Caltech

    August 17, 2017
    Elizabeth Landau
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-354-6425
    elizabeth.landau@jpl.nasa.gov

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    This artist’s concept shows a brown dwarf with bands of clouds, thought to resemble those seen at Neptune and the other outer planets. Credit: NASA/JPL-Caltech

    Dim objects called brown dwarfs, less massive than the Sun but more massive than Jupiter, have powerful winds and clouds — specifically, hot patchy clouds made of iron droplets and silicate dust. Scientists recently realized these giant clouds can move and thicken or thin surprisingly rapidly, in less than an Earth day, but did not understand why.

    Now, researchers have a new model for explaining how clouds move and change shape in brown dwarfs, using insights from NASA’s Spitzer Space Telescope. Giant waves cause large-scale movement of particles in brown dwarfs’ atmospheres, changing the thickness of the silicate clouds, researchers report in the journal Science. The study also suggests these clouds are organized in bands confined to different latitudes, traveling with different speeds in different bands.

    “This is the first time we have seen atmospheric bands and waves in brown dwarfs,” said lead author Daniel Apai, associate professor of astronomy and planetary sciences at the University of Arizona in Tucson.

    Just as in Earth’s ocean, different types of waves can form in planetary atmospheres. For example, in Earth’s atmosphere, very long waves mix cold air from the polar regions to mid-latitudes, which often lead clouds to form or dissipate.

    The distribution and motions of the clouds on brown dwarfs in this study are more similar to those seen on Jupiter, Saturn, Uranus and Neptune. Neptune has cloud structures that follow banded paths too, but its clouds are made of ice. Observations of Neptune from NASA’s Kepler spacecraft, operating in its K2 mission, were important in this comparison between the planet and brown dwarfs.

    “The atmospheric winds of brown dwarfs seem to be more like Jupiter’s familiar regular pattern of belts and zones than the chaotic atmospheric boiling seen on the Sun and many other stars,” said study co-author Mark Marley at NASA’s Ames Research Center in California’s Silicon Valley.

    Brown dwarfs can be thought of as failed stars because they are too small to fuse chemical elements in their cores. They can also be thought of as “super planets” because they are more massive than Jupiter, yet have roughly the same diameter. Like gas giant planets, brown dwarfs are mostly made of hydrogen and helium, but they are often found apart from any planetary systems. In a 2014 study using Spitzer, scientists found that brown dwarfs commonly have atmospheric storms.

    Due to their similarity to giant exoplanets, brown dwarfs are windows into planetary systems beyond our own. It is easier to study brown dwarfs than planets because they often do not have a bright host star that obscures them.

    “It is likely the banded structure and large atmospheric waves we found in brown dwarfs will also be common in giant exoplanets,” Apai said.

    Using Spitzer, scientists monitored brightness changes in six brown dwarfs over more than a year, observing each of them rotate 32 times. As a brown dwarf rotates, its clouds move in and out of the hemisphere seen by the telescope, causing changes in the brightness of the brown dwarf. Scientists then analyzed these brightness variations to explore how silicate clouds are distributed in the brown dwarfs.

    Researchers had been expecting these brown dwarfs to have elliptical storms resembling Jupiter’s Great Red Spot, caused by high-pressure zones. The Great Red Spot has been present in Jupiter for hundreds of years and changes very slowly: Such “spots” could not explain the rapid changes in brightness that scientists saw while observing these brown dwarfs. The brightness levels of the brown dwarfs varied markedly just over the course of an Earth day.

    To make sense of the ups and downs of brightness, scientists had to rethink their assumptions about what was going on in the brown dwarf atmospheres. The best model to explain the variations involves large waves, propagating through the atmosphere with different periods. These waves would make the cloud structures rotate with different speeds in different bands.

    University of Arizona researcher Theodora Karalidi used a supercomputer and a new computer algorithm to create maps of how clouds travel on these brown dwarfs.

    “When the peaks of the two waves are offset, over the course of the day there are two points of maximum brightness,” Karalidi said. “When the waves are in sync, you get one large peak, making the brown dwarf twice as bright as with a single wave.”

    The results explain the puzzling behavior and brightness changes that researchers previously saw. The next step is to try to better understand what causes the waves that drive cloud behavior.

    See the full article here .

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  • richardmitnick 9:45 am on July 13, 2017 Permalink | Reply
    Tags: "Planetary mass binary", , , , Brown Dwarfs, , , L7 dwarf 2MASS J11193254–1137466, TW Hydrae Association   

    From Centauri Dreams: “A Binary ‘Rogue’ Planet?” 

    Centauri Dreams

    July 12, 2017
    Paul Gilster

    “Planetary mass binary” is an unusual term, but one that seems to fit new observations of what was thought to be a brown dwarf or free-floating large Jupiter analog, and now turns out to be two objects, each of about 3.7 Jupiter masses. That puts them into planet-range when it comes to mass, as the International Astronomical Union normally considers objects below the minimum mass to fuse deuterium (13 Jupiter masses) to be planets. This is the lowest mass binary yet discovered.

    A team led by William Best (Institute for Astronomy, University of Hawaii) went to work on the L7 dwarf 2MASS J11193254–1137466 with the idea of determining what they assumed to be the single object’s mass and age. It was through observations with the Keck II telescope in Hawaii that they discovered the binary nature of their target.


    Keck Observatory, Mauna Kea, Hawaii, USA

    The separation between the two objects is about 3.9 AU, based upon the assumption that the binary is around 160 light years away, the distance of the grouping of stars called the TW Hydrae Association.

    Let’s pause on this for a moment. The TW Hydrae Association has come up in these pages in the past, as a so-called ‘moving group’ that contains stars that share a common origin, and thus are similar in age and travel through space together. Moving groups are obviously useful — if astronomers can determine that a star is in one, then its age and distance can be inferred from the other stars in the group. Best and colleagues determined from key factors like sky position, proper motion, and radial velocity that there was about an 80 percent chance that 2MASS J11193254–1137466AB is a member of the TW Hydrae Association.

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    Keck images of 2MASS J11193254–1137466 reveal that this object is actually a binary system. A similar image of another dwarf, WISEA J1147-2040, is shown at bottom left for contrast: this one does not show signs of being a binary at this resolution. Credit: Best et al. 2017.

    Determining a brown dwarf’s age is tricky business because these objects cool continuously as they age, which means that brown dwarfs of different masses and ages can wind up with the same luminosity. The authors point out that this mass-age-luminosity degeneracy makes it hard to figure out their characteristics without knowing at least two of the three parameters. Membership in a moving group like the TW Hydrae Association gives us an age of about 10 million years but also provides mass estimates from evolutionary models.

    And a binary system hits the jackpot, for now we can study the orbits of the two objects to work out model-independent masses, which is how Best drilled down to the 3.7 Jupiter mass result for each binary member here. The authors consider the binary a benchmark for tests of evolutionary and atmospheric models of young planets, and go on to speculate about its possible origins:

    “The isolation of 2MASS J1119−1137AB strongly suggests that it is a product of normal star formation processes, which therefore must be capable of making binaries with ≲ 5 MJup components. 2MASS J1119−1137AB could be a fragment of a higher-order system that was ejected via dynamical interactions (Reipurth & Mikkola 2015 ApJ), although the lack of any confirmed member of TWA within 10° (projected separation ≈ 5 pc) of 2MASS J1119−1137 makes this scenario unlikely. Formation of very low mass binaries in extended massive disks around Sun-like stars followed by ejection into the field has been proposed by, e.g., Stamatellos & Whitworth (2009), but disks of this type have not been observed.”

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    The positions of 2MASS J11193254–1137466A and B on a color-magnitude diagram for ultracool dwarfs. The binary components lie among the faintest and reddest planetary-mass L dwarfs. Credit: Best et al. 2017.

    So there is much to learn here. An object’s composition, temperature and formation history all come into play when determining whether it is a brown dwarf or a planet, and some definitions of brown dwarf take us below the 13 Jupiter mass criteria. But at 3.7 Jupiter masses, these objects clearly warrant the authors’ careful tag of “planetary mass binary.”

    The paper is Best et al., The Young L Dwarf 2MASS J11193254−1137466 Is a Planetary-mass Binary, Astrophysical Journal Letters Vol. 843, No. 1 (23 June 2017).

    Centauri Dreams


    See the full article here .

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    Tracking Research into Deep Space Exploration

    Alpha Centauri and other nearby stars seem impossible destinations not just for manned missions but even for robotic probes like Cassini or Galileo. Nonetheless, serious work on propulsion, communications, long-life electronics and spacecraft autonomy continues at NASA, ESA and many other venues, some in academia, some in private industry. The goal of reaching the stars is a distant one and the work remains low-key, but fascinating ideas continue to emerge. This site will track current research. I’ll also throw in the occasional musing about the literary and cultural implications of interstellar flight. Ultimately, the challenge may be as much philosophical as technological: to reassert the value of the long haul in a time of jittery short-term thinking.

     
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