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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

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  • 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

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    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.

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    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

    5
    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

    1

    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.

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    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!

    5
    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

    1
    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.

     
  • richardmitnick 12:38 pm on July 6, 2017 Permalink | Reply
    Tags: 100 billion brown dwarfs may populate our galaxy, , , , Brown Dwarfs, ,   

    From COSMOS: “100 billion brown dwarfs may populate our galaxy” 

    Cosmos Magazine bloc

    COSMOS

    06 July 2017
    Michael Lucy

    1
    An artist’s impression of a brown dwarf. NASA / JPL-Caltech.

    The Milky Way may contain as many as 100 billion brown dwarfs, according to new research to be published in the Monthly Notices of the Royal Astronomical Society.

    Brown dwarfs are failed stars that were not quite heavy enough to sustain the hydrogen fusion reactions that make real stars shine. They weigh about 10 to 100 times as much as Jupiter, which means their internal gravitational pressure is enough to fuse deuterium (a kind of hydrogen that contains an extra neutron in each atom) and sometimes also lithium. This means they glow only dimly. Most of the radiation they do give off is in the infrared spectrum and hence invisible to the human eye, though some would appear faintly purple or red.

    All of this makes brown dwarfs very hard for astronomers to spot. While scientists have speculated since the 1960s that they might exist, the first definite sightings did not occur until 1995.

    The new research, by an international team of astronomers lead by Koraljka Muzic from the University of Lisbon and Aleks Scholz from the University of St Andrews, used the European Southern Observatory’s Very Large Telescope to make infrared observations of distant dense star clusters where many new stars were being formed.

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

    They counted as many brown dwarfs as they could, and came to the conclusion there were about half as many brown dwarfs as stars.

    Earlier studies of brown dwarfs – which focused mainly on regions nearer to Earth where stars are less dense, simply because they are easier to see if they are closer – concluded the substellar objects were much less common.

    The researchers estimate the minimum number of brown dwarfs in the Milky Way is at least 25 billion and as high as 100 billion – but they note even this upper figure may be an underestimate, given the probability of there being many more failed stars too faint to see at all.

    See the full article here .

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  • richardmitnick 3:08 pm on May 9, 2017 Permalink | Reply
    Tags: , , , Brown Dwarfs, , , Surprise! When a brown dwarf is actually a planetary mass object   

    From Carnegie: “Surprise! When a brown dwarf is actually a planetary mass object” 

    Carnegie Institution for Science
    Carnegie Institution for Science

    May 09, 2017
    No writer credit found

    1
    An artist’s conception of SIMP J013656.5+093347, or SIMP0136 for short, which the research team determined is a planetary like member of a 200-million-year-old group of stars called Carina-Near. Image is courtesy of NASA/JPL, slightly modified by Jonathan Gagné.

    Sometimes a brown dwarf is actually a planet—or planet-like anyway. A team led by Carnegie’s Jonathan Gagné, and including researchers from the Institute for Research on Exoplanets (iREx) at Université de Montréal, the American Museum of Natural History, and University of California San Diego, discovered that what astronomers had previously thought was one of the closest brown dwarfs to our own Sun is in fact a planetary mass object.

    Their results are published by The Astrophysical Journal Letters.

    Smaller than stars, but bigger than giant planets, 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. So after formation, brown dwarfs slowly cool down and contract over time. The contraction usually ends after a few hundred million years, although the cooling is continuous.

    “This means that the temperatures of brown dwarfs can range from as hot as stars to as cool as planets, depending on how old they are,” said the AMNH’s Jackie Faherty, a co-author on this discovery.

    The team determined that a well-studied object known as SIMP J013656.5+093347, or SIMP0136 for short, is a planetary like member of a 200-million-year-old group of stars called Carina-Near.

    Groups of similarly aged stars moving together through space are considered prime regions to search for free-floating planetary like objects, because they provide the only means of age-dating these cold and isolated worlds. Knowing the age, as well as the temperature, of a free-floating object like this is necessary to determine its mass.

    Gagné and the research team were able to demonstrate that at about 13 times the mass of Jupiter, SIMP0136 is right at the boundary that separates brown dwarf-like properties, primarily the short-lived burning of deuterium in the object’s core, from planet-like properties.

    Free-floating planetary mass objects are valuable because they are very similar to gas giant exoplanets that orbit around stars, like our own Solar System’s Jupiter or Saturn, but it is comparatively much easier to study their atmospheres. Observing the atmospheres of exoplanets found within distant star systems is challenging, because dim light emitted by those orbiting exoplanets is overwhelmed by the brightness of their host stars, which blinds the instruments that astronomers use to characterize an exoplanet’s atmospheres.

    “The implication that the well-known SIMP0136 is actually more planet-like than we previously thought will help us to better understand the atmospheres of giant planets and how they evolve,” Gagné said.

    They may be easier to study in great detail, but these free-floating worlds are still extremely hard to discover unless scientists spend a lot of time observing them at the telescope, because they can be located anywhere in the sky and they are very hard to tell apart from brown dwarfs or very small stars. For this reason, researchers have confirmed only a handful of free-floating planetary like objects so far.

    Étienne Artigau, co-author and leader of the original SIMP0136 discovery, added: “This newest addition to the very select club of free-floating planetary like objects is particularly remarkable, because we had already detected fast-evolving weather patterns on the surface of SIMP0136, back when we thought it was a brown dwarf.”

    In a field where analyzing exoplanet atmospheres is of the utmost interest, having already seen evidence of weather patterns on an easier-to-observe free-floating object that exists away from the brightness of its host star is an exciting realization.

    Other members of the research team were: Adam Burgasser and Daniella Bardalez Gagliuffi of University of California San Diego and Sandie Bouchard, Loïc Albert, David LaFrenière, and René Doyon of iREx.

    See the full article here .

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    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 7:31 am on October 4, 2016 Permalink | Reply
    Tags: Astronomers find a treasure trove of strange brown dwarfs, , , , Brown Dwarfs   

    From Astronomy: “Astronomers find a treasure trove of strange brown dwarfs” 

    Astronomy magazine

    astronomy.com

    October 03, 2016
    Mika McKinnon

    The new find adds to the population of “failed stars” and makes them even weirder than we thought.

    1
    NASA/JPL-Caltech/UCLA

    Stars that didn’t quite make it to full blazing glory are a lot more common than we thought. A new survey found not just more brown dwarfs, but an entire population of ultracool brown dwarfs that aren’t identified by standard sky surveys.

    Brown dwarfs are often teased as being failed stars, too big and bright to be a planet but too small to sustain hydrogen fusion. They’re doomed to stay dim until they sputter out, never achieving the bright twinkle of the stars that spot our skies. But this makes them perfect for observation: unlike other stars, brown dwarfs are dim enough to not blind instruments. They’re often in isolation, allowing for even more clear observation of this astrophysical intermediary between planets and stars.

    A new survey led by Jasmin Robert of Université de Montréal went hunting for even more brown dwarfs. The team surveyed 28% of the sky, and checked the properties of every star. Instead of using the standard techniques to filter out brown dwarfs strictly by set color ranges, the team pulled full spectrums of stars to find more unusual brown dwarfs. They found an additional 165 ultracool brown dwarfs not previously identified within the study region. For brown dwarfs, ultracool is below 3,500F, a sixth the temperature of our Sun and barely warm enough to melt carbon.

    Of the stars Robert and her team found, fully a third were unusual even in this odd population. The unusual ultracool brown dwarfs are ones that have different colors than anticipated for their age. They either appeared older than they are, tinted red through a disproportionally dusty atmosphere or inflated size, or younger than they are by being tinted blue by a scarcity of dust or contracted size. The discovery that the team identified so many unusual brown dwarfs so quickly in such a small patch of sky indicates that the population of brown dwarfs is more varied than we thought.

    All of this means that it’s just gotten a whole lot easier to go hunting for brown dwarfs in the neighborhood.

    See the full article here .

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