Tagged: CfA Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 7:17 am on August 11, 2018 Permalink | Reply
    Tags: , , , CfA, , ,   

    From Center For Astrophysics: “Spitzer Infrared Observations of a Gravitational Wave Source – a Binary Neutron Star Merger” 

    Harvard Smithsonian Center for Astrophysics


    From Center For Astrophysics

    GW170817 is the name given to a gravitational wave signal seen by the LIGO and Virgo detectors on 17 August 2017.

    14
    See https://sciencesprings.wordpress.com/2017/10/20/from-ucsc-neutron-stars-gravitational-waves-and-all-the-gold-in-the-universe/


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Lasting for about 100 seconds, the signal was produced by the merger of two neutron stars. The observation was then confirmed – the first time this has happened for gravitational waves – by observations with light waves: the preceding five detections of merging black holes did not have (and were not expected to have) any detectable electromagnetic signals. The light from the neutron star merger is produced by the radioactive decay of atomic nuclei created in the event. (Neutron star mergers do more than just produce optical light, by the way: they are also responsible for making most of the gold in the universe.) Numerous ground-based optical observations of the merger concluded that the decaying atomic nuclei fall into at least two groups, a rapidly evolving and fast moving one composed of elements less massive than Lanthanide Series elements, and one that is more slowly evolving and dominated by heavier elements.

    Ten days after the merger, the continuum emission peaked at infrared wavelengths with a temperature of approximately 1300 kelvin, and continued to cool and dim. The Infrared Array Camera (IRAC) on the Spitzer Space Telescope observed the region around GW170817 for 3.9 hours in three epochs 43, 74 and 264 days after the event (SAO is the home of IRAC PI Fazio and his team). The shape and evolution of the emission reflect the physical processes at work, for example, the fraction of heavy elements in the ejecta or the possible role of carbon dust. Tracking the flux over time enables the astronomers to refine their models and understanding of what happens when neutron stars merge.

    A team of CfA astronomers, Victoria Villar, Philip Cowperthwaite, Edo Berger, Peter Blanchard, Sebastian Gomez, Kate Alexander, Tarraneh Eftekhari, Giovanni Fazio, James Guillochon, Joe Hora, Matthew Nicholl, and Peter Williams and two colleagues participated in an effort to measure and interpret the infrared observations. The source was extremely faint and moreover lies close to a very bright point source. Using a novel algorithm to prepare and subtract the IRAC images to eliminate the constant-brightness objects, the team was able to spot the merger source clearly in the first two epochs, although it was fainter than was predicted by the models by more than about a factor of two. It had dimmed beyond detection by the third epoch. However the rate of dimming and the infrared colors are consistent with models; at these epochs the material had cooled down to about 1200 kelvin. The team suggests several possible reasons for the surprising faintness, including possible transformation of the ejecta into a nebulous phase and notes that the new dataset will help refine the models.

    The scientists conclude by emphasizing that future binary star merger detections (an improved LISA will begin observing again in 2019) will similarly benefit from infrared observations, and that characterization of the infrared will enable more accurate determination of the nuclear decay processes underway. Their current paper, moreover, shows that Spitzer should be able to spot binary mergers as far away as four hundred million light-years, about the distance that the improved LISA should be able to probe.

    Spitzer Space Telescope Infrared Observations of the Binary Neutron Star Merger GW170817
    The Astrophysical Journal Letters

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

    Advertisements
     
  • richardmitnick 6:57 am on August 11, 2018 Permalink | Reply
    Tags: , , , CfA, , Ready for Its Day in the Sun: The SWEAP Investigation,   

    From Center For Astrophysics: “Ready for Its Day in the Sun: The SWEAP Investigation” 

    Harvard Smithsonian Center for Astrophysics


    From Center For Astrophysics

    August 3, 2018
    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    1

    When NASA’s Parker Solar Probe launches into space from the Kennedy Space Center, it will begin its journey to the Sun, our nearest star. The Parker Solar Probe will travel almost 90 million miles and eventually enter through the Sun’s outer atmosphere to encounter a dangerous environment of intense heat and solar radiation. During this harrowing journey, it will fly closer to the Sun than any other human-made object.

    To revolutionize our understanding of our most important and life-sustaining star, scientists and engineers have built a suite of instruments aboard the Parker Solar Probe to conduct different experiments. Some of these instruments will be protected by a thick carbon-composite heat shield. However, others will be more exposed.

    The Solar Wind Electrons Alphas and Protons (SWEAP) investigation is the set of instruments that will directly measure the hot ionized gas in the solar atmosphere during the solar encounters. A key instrument on SWEAP called the Solar Probe Cup (SPC) was built at the Smithsonian Astrophysical Observatory (SAO) in Cambridge, Mass.

    The SPC is a small metal device that will peer around the protective heat shield of the spacecraft directly at the Sun. It will face some of the most extreme conditions ever encountered by a scientific instrument, and allow a sample of the Sun’s atmosphere to be swept up for the first time.

    The SPC uses high voltages to determine what type of particles can enter, which is a way of measuring the energy of the particle. This is crucial information for probing the wind of hot ionized gas that is constantly produced by the Sun. As the spacecraft flies towards the Sun for an encounter, the wind is directed straight into the cup. Without the SPC, Parker Solar Probe would miss most of what is in between Earth and the Sun. This unique probe of the solar wind is important for scientists to better understand space weather, which is responsible for effects that range from endangering astronauts on space walks to impacting the electronics in communications satellites.

    The Parker Solar Probe spacecraft, about the size of a small car, will travel towards the Sun’s atmosphere at speeds of about 430,000 mph (700,000 km/hr), becoming the fastest human-made object. Eventually, Parker Solar Probe will enter an orbit that approaches to within only 4 million miles from the star’s surface. (For context, the Earth averages a distance of about 93 million miles from the Sun during its elliptical orbit. Or, to put it another way, the spacecraft will travel about 96% of the way from the Earth to the Sun.) Parker Solar Probe, which will be carried into space by a Delta-IV Heavy rocket, is currently scheduled to launch on August 11, 2018.

    The SWEAP Team is led by Justin Kasper currently at the University of Michigan (and currently an SAO Research Associate). On the SWEAP Investigation, SAO partners with team members from University of California, Berkeley Space Sciences Laboratory, the NASA Marshall Space Flight Center, the University of Alabama Huntsville, NASA Goddard Space Flight Center, Los Alamos National Laboratory, and the Massachusetts Institute of Technology. SAO built the SPC (Instrument Scientist: Tony Case), leads the Science Operations Center (Head of Science Operations: Kelly Korreck), and manages the overall SWEAP program.

    More information on SAO’s role in Parker Solar Probe can be found at:

    “Extreme Spacecrafting: NASA’s Parker Solar Probe”
    Video of Observatory Night talk by Anthony Case and Kelly Korreck on May 17, 2018

    “Parker Solar Probe’s Mission to Solve Stranger Things”
    Post by Kelly Korreck at National Air & Space Museum’s blog

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 2:09 pm on July 2, 2018 Permalink | Reply
    Tags: , , , CfA, , Kepler-186f, More Clues That Earth-Like Exoplanets Are Indeed Earth-Like   

    From Harvard-Smithsonian Center for Astrophysics: “More Clues That Earth-Like Exoplanets Are Indeed Earth-Like” 

    Harvard Smithsonian Center for Astrophysics


    June 29, 2018

    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    From Harvard-Smithsonian Center for Astrophysics

    1
    This artist’s concept depicts Kepler-186f. NASA Ames/JPL-Caltech/T. Pyle

    A new study provides new clues indicating that an exoplanet 500 light-years away is much like Earth.

    Kepler-186f is the first identified Earth-sized planet outside the Solar System orbiting a star in the habitable zone. This means it’s the proper distance from its host star for liquid water to pool on the surface.

    The Georgia Tech study used simulations to analyze and identify the exoplanet’s spin axis dynamics. Those dynamics determine how much a planet tilts on its axis and how that tilt angle evolves over time. Axial tilt contributes to seasons and climate because it affects how sunlight strikes the planet’s surface.

    The researchers suggest that Kepler-186f’s axial tilt is very stable, much like the Earth, making it likely that it has regular seasons and a stable climate. The Georgia Tech team thinks the same is true for Kepler-62f, a super-Earth-sized planet orbiting around a star about 1,200 light-years away from us.

    How important is axial tilt for climate? Large variability in axial tilt could be a key reason why Mars transformed from a watery landscape billions of years ago to today’s barren desert.

    “Mars is in the habitable zone in our solar system, but its axial tilt has been very unstable — varying from 0 to 60 degrees,” said Georgia Tech Assistant Professor Gongjie Li, who led the study together with graduate student Yutong Shan from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass. “That instability probably contributed to the decay of the Martian atmosphere and the evaporation of surface water.”

    As a comparison, Earth’s axial tilt oscillates more mildly — between 22.1 and 24.5 degrees, going from one extreme to the other every 10,000 or so years.

    The orientation angle of a planet’s orbit around its host star can be made to oscillate by gravitational interaction with other planets in the same system. If the orbit were to oscillate at the same speed as the precession of the planet’s spin axis (akin to the circular motion exhibited by the rotation axis of a top or gyroscope), the spin axis would also wobble back and forth, sometimes dramatically.

    Mars and Earth interact strongly with each other, as well as with Mercury and Venus. As a result, by themselves, their spin axes would precess with the same rate as the orbital oscillation, which may cause large variations in their axial tilt. Fortunately, the Moon keeps Earth’s variations in check. The Moon increases our planet’s spin axis precession rate and makes it differ from the orbital oscillation rate. Mars, on the other hand, doesn’t have a large enough satellite to stabilize its axial tilt.

    “It appears that both exoplanets are very different from Mars and the Earth because they have a weaker connection with their sibling planets,” said Li, a faculty member in the School of Physics. “We don’t know whether they possess moons, but our calculations show that even without satellites, the spin axes of Kepler-186f and 62f would have remained constant over tens of millions of years.”

    Kepler-186f is less than 10 percent larger in radius than Earth, but its mass, composition, and density remain a mystery. It orbits its host star every 130 days. According to NASA, the brightness of that star at high noon, while standing on 186f, would appear as bright as the sun just before sunset here on Earth. Kepler-186f is located in the constellation Cygnus as part of a five-planet star system.

    Kepler-62f was the most Earth-like exoplanet until scientists noticed 186f in 2014. It’s about 40 percent larger than our planet and is likely a terrestrial or ocean-covered world. It’s in the constellation Lyra and is the outermost planet among five exoplanets orbiting a single star.

    That’s not to say either exoplanet has water, let alone life. But both are relatively good candidates.

    “Our study is among the first to investigate climate stability of exoplanets and adds to the growing understanding of these potentially habitable nearby worlds,” said Li.

    “I don’t think we understand enough about the origin of life to rule out the possibility of its presence on planets with irregular seasons,” added the CfA’s Shan. “Even on Earth, life is remarkably diverse and has shown incredible resilience in extraordinarily hostile environments.

    “But a climatically stable planet might be a more comfortable place to start.”

    A paper describing these results appeared in the May 17, 2018 issue of The Astronomical Journal.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 12:35 pm on June 20, 2018 Permalink | Reply
    Tags: , , , CfA, , XMM-Newton Finds Missing Intergalactic Material   

    From Harvard-Smithsonian Center for Astrophysics: “XMM-Newton Finds Missing Intergalactic Material” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    June 20, 2018
    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    ESA/XMM Newton

    1
    This figure shows the filamentary structure of the hot gas that represents part of the warm-hot intergalactic medium (WHIM). It is based on a simulation extending over more than 200 million light years. The red and orange regions have the highest densities & the green regions have lower densities. Princeton University/Renyue Cen

    2
    Astronomers have used ESA’s XMM-Newton space observatory (lower right) to detect the WHIM. The white box encloses the filamentary structure of the hot gas that represents part of the WHIM. It is based on a cosmological simulation extending over more than 200 million light years. The red and orange regions have the highest densities & the green regions have lower densities. The discovery was made using observations of a distant quasar – a supermassive black hole that is actively devouring matter and shining brightly from X-rays to radio waves (upper left). The team found the signature of oxygen in the WHIM lying between the observatory and the quasar, at two different locations along the line of sight (shown in the spectrum in the lower left with green and magenta arrows). The blue arrows are signatures of nitrogen in our Milky Way galaxy.
    Illustrations and composition: ESA / ATG medialab; data: ESA / XMM-Newton / F. Nicastro et al. 2018; cosmological simulation: Princeton University/Renyue Cen

    3
    The mysterious dark matter and dark energy make up about 25 and 70 percent of our cosmos respectively, and ordinary matter, which makes up everything we see, including galaxies, stars and planets – amounts to only about five percent. However, stars in galaxies across the Universe only make up about seven percent of all ordinary matter and the cold and hot interstellar gas that permeates galaxies and galaxy clusters together accounts for only about 11 percent. Most of the Universe’s ordinary matter, or baryons, lurks in the cosmic web, the filamentary distribution of both dark and ordinary matter that extends throughout the Universe. In the past astronomers were able to locate a good chunk of the cool and warm parts of this intergalactic material (about 43 percent of all baryons in total). Astronomers have now used ESA’s XMM-Newton space observatory to detect the hot component of this intergalactic material along the line of sight to a quasar. The amount of hot intergalactic gas detected in these observations amounts up to 40 percent of all baryons in the Universe, closing the gap in the overall budget of ordinary matter in the cosmos. ESA

    After a nearly twenty-year long game of cosmic hide-and-seek, astronomers using ESA’s XMM-Newton space observatory have finally found evidence of hot, diffuse gas permeating the cosmos, closing a puzzling gap in the overall budget of ‘normal’ matter in the Universe.

    While the mysterious dark matter and dark energy make up about 25 and 70 percent of our cosmos respectively, the ordinary matter that makes up everything we see – from stars and galaxies to planets and people – amounts to only about five percent.

    But even this five percent turns out to be hard to track down.

    The total amount of ordinary matter, which astronomers refer to as baryons, can be estimated from observations of the Cosmic Microwave Background [CMB], which is the most ancient light in the history of the Universe, dating back to only about 380,000 years after the Big Bang.

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    Observations of very distant galaxies allow astronomers to follow the evolution of this matter throughout the Universe’s first couple of billions of years. After that, however, more than half of it seemed to have gone missing.

    “The missing baryons represent one of the biggest mysteries in modern astrophysics,” explains Fabrizio Nicastro, lead author of the paper presenting a solution to the mystery, published today in Nature. Nicastro is from the INAF-Osservatorio Astronomico di Roma, Italy, and the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass.

    “We know this matter must be out there, we see it in the early Universe, but then we can no longer get hold of it. Where did it go?”

    Counting the population of stars in galaxies across the Universe, plus the interstellar gas that permeates galaxies – the raw material to create stars – only gets as far as a mere ten percent of all ordinary matter. Adding up the hot, diffuse gas in the haloes that encompass galaxies and the even hotter gas that fills galaxy clusters, which are the largest cosmic structures held together by gravity, raises the inventory to less than twenty percent.

    This is not surprising: stars, galaxies and galaxy clusters form in the densest knots of the cosmic web, the filamentary distribution of both dark and ordinary matter that extends throughout the Universe. While these sites are dense, they are also rare, so not the best spots to look for the majority of cosmic matter.

    Astronomers suspected that the ‘missing’ baryons must be lurking in the ubiquitous filaments of this cosmic web, where matter is, however, less dense and therefore more challenging to observe. Using different techniques over the years, they were able to locate a good chunk of this intergalactic material – mainly its cool and warm components – bringing up the total budget to a respectable 60 percent, but leaving the overall mystery still unsolved.

    Nicastro and many other astronomers around the world have been on the tracks of the remaining baryons for almost two decades, ever since X-ray observatories such as ESA’s XMM-Newton and NASA’s Chandra X-ray Observatory became available to the scientific community.

    Observing in this portion of the electromagnetic spectrum, they can detect hot intergalactic gas, with temperatures around a million degrees or more, that is blocking the X-rays emitted by even more distant sources.

    For this project, Nicastro and his collaborators used XMM-Newton to look at a quasar – a massive galaxy with a supermassive black hole at its center that is actively devouring matter and shining brightly from X-rays to radio waves. They observed this quasar, whose light takes more than four billion years to reach us, for a total of 18 days, split between 2015 and 2017, in the longest X-ray observation ever performed of such a source.

    “After combing through the data, we succeeded at finding the signature of oxygen in the hot intergalactic gas between us and the distant quasar, at two different locations along the line of sight,” says Nicastro.

    “This is happening because there are huge reservoirs of material – including oxygen – lying there, and just in the amount we were expecting, so we finally can close the gap in the baryon budget of the Universe.”

    This extraordinary result is the beginning of a new quest. Observations of different sources across the sky are needed to confirm whether these findings are truly universal, and to further investigate the physical state of this long-sought-for matter.

    Fabrizio and his colleagues are planning to study more quasars with XMM-Newton and Chandra in the coming years. To fully explore the distribution and properties of this so-called warm-hot intergalactic medium, however, more sensitive instruments will be needed, like ESA’s Athena, the Advanced Telescope for High-Energy Astrophysics, scheduled for launch in 2028.

    ESA/Athena spacecraft depiction

    “The discovery of the missing baryons with XMM-Newton is the exciting first step to fully characterize the circumstances and structures in which these baryons are found,” says co-author Jelle Kaastra from the Netherlands Institute for Space Research.

    “For the next steps, we will need the much higher sensitivity of Athena, which has the study of the warm-hot intergalactic medium as one of its main goals, to improve our understanding of how structures grow in the history of the Universe.”

    “It makes us very proud that XMM-Newton was able to discover the weak signal of this long elusive material, hidden in a million-degree hot fog that extends through intergalactic space for hundreds of thousands of light years,” says Norbert Schartel, XMM-Newton project scientist at ESA.

    “Now that we know these baryons are no longer missing, we can’t wait to study them in greater detail.”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 3:17 pm on May 30, 2018 Permalink | Reply
    Tags: , , , CfA, , Parker Solar Probe's Faraday cup,   

    From Harvard-Smithsonian Center for Astrophysics and U Michigan : “Key Parker Solar Probe Sensor Bests Sun Simulator—Last Launch Hurdle” 

    U Michigan bloc

    University of Michigan

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    April 30, 2018
    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    1
    Researchers use a quartet of IMAX projectors to create the light and heat the Parker Solar Probe cup will experience during its trips through the sun’s atmosphere. The cup sits inside a vacuum chambers set up in a lab at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts. Image credit: Levi Hutmacher, Michigan Engineering

    2
    Artist’s concept of the Parker Solar Probe spacecraft approaching the sun. In order to unlock the mysteries of the corona, but also to protect a society that is increasingly dependent on technology from the threats of space weather, we will send Parker Solar Probe to touch the sun. Image credit: NASA

    3
    Justin Kasper, (left), a University of Michigan associate professor of climate and space sciences engineering, awaits test results with Anthony Case, an astrophysicist at the Harvard Smithsonian Institute for Astrophysics. Image creidt: Levi Hutmacher, Michigan Engineering

    You don’t get to swim in the sun’s atmosphere unless you can prove you belong there. And the Parker Solar Probe’s Faraday cup, a key sensor aboard the $1.5 billion NASA mission launching this summer, earned its stripes last week by enduring testing in a homemade contraption designed to simulate the sun.

    The cup will scoop up and examine the solar wind as the probe passes closer to the sun than any previous manmade object. Justin Kasper, University of Michigan associate professor of climate and space sciences and engineering, is principal investigator for Parker’s Solar Wind Electrons Alphas and Protons (SWEAP) investigation.

    In order to confirm the cup will survive the extreme heat and light of the sun’s corona, researchers previously tortured a model of the Faraday cup at temperatures exceeding 3,000 degrees Fahrenheit, courtesy of the Oak Ridge National Laboratory’s Plasma Arc Lamp. The cup, built from refractory metals and sapphire crystal insulators, exceeded expectations.

    But the final test took place last week, in a homemade contraption Kasper and his research team call the Solar Environment Simulator. While being blasted with roughly 10 kilowatts of light on its surface—enough to heat a sheet of metal to 1,800 degrees Fahrenheit in seconds—the Faraday cup model ran through its paces, successfully scanning a simulated stream of solar wind.

    “Watching the instrument track the signal from the ion beam as if it was plasma flowing from the sun was a thrilling preview of what we will see with Parker Solar Probe,” Kasper said.

    Roilings in the sun’s atmosphere can violently fling clouds of plasma into space, known as coronal mass ejections, sometimes directly at Earth. Without precautionary measures, such clouds can set up geomagnetic oscillations around Earth that can trip up satellite electronics, interfere with GPS and radio communications and—at their worst—can create surges of current through power grids that can overload and disrupt the system for extended periods of time, up to months.

    By understanding what makes up the solar corona and what drives the constant outpouring of solar material from the sun, scientists on Earth will be better equipped to interpret the solar activity we see from afar and create a better early-warning system. That’s where Parker Solar Probe, slated for launch on July 31, 2018, comes in, with its complement of experiments that includes the Faraday cup.

    To test the cup model, researchers had to create something new. Their simulator sits in a first-floor lab at the Smithsonian Astrophysical Observatory in Cambridge, Mass., and embodies the adage that necessity is the mother of invention.

    It has the look of a makeshift operating room, with a metal frame holding up thick blue tarps around three sides creating a 16×8 workspace.

    Inside the area, recreating the sun’s heat and light fell to a quartet of modified older model IMAX projectors that Kasper’s team purchased on eBay for a few thousand dollars apiece. These are not the digital machines you find in today’s Cineplexes, but an earlier generation that utilized bulbs.

    “It turns out a movie theater bulb on an IMAX projector runs at about the same 5,700 degrees Kelvin—the same effective temperature as the surface of the sun,” Kasper said. “And it gives off nearly the same spectrum of light as the surface.”

    Space offers essentially no atmosphere, meaning a proper testing environment for the Faraday cup would have as little air as possible. So researchers placed the cup in a metal vacuum chamber for testing.

    Resembling an iron lung, the seven-foot-long silver chamber has a hatch at one end that swings outward and has a small round window in it. The night before testing, the team began pumping the atmosphere out of the vacuum chamber.

    By the time the simulation cranked up for testing, the chamber registered roughly one-billionth of the Earth’s atmosphere.

    All four of the IMAX projectors sit atop wheeled tables, and to set up for the test, researchers rolled them into place, with their beams pointed through the vacuum tube window directly at the Faraday cup.

    The final element of the simulator is its ability to generate the kinds of particles the Faraday cup will need to sense and evaluate. To do that, the team attached an ion gun to the vacuum tube hatch, with the “barrel” of the device reaching inside and pointed at the cup.

    “The ion gun takes a pellet of metal and heats it up,” said Anthony Case, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics. “When it gets hot, ions start boiling off this piece of metal. Then you hook it up to a battery, accelerating the ions out of the gun. And we can direct them right toward the Faraday cup’s aperture where they’ll be measured.”

    In this final test, the Faraday cup took the heat and delivered—putting Parker Solar Probe on track for its summer launch.

    Kelly Korreck, a U-M alumna and astrophysicist at the institute, serves as head of science operations on Parker’s SWEAP investigation as well as SWEAP activities for the Smithsonian.

    “As for the test today, it confirmed what I had suspected—when you take an amazing team of scientists and engineers, give them a complex, difficult, interesting project and the motivation of exploring a region of the universe humankind has never been to, before remarkable things happen,” she said.

    See the full CfA article here .
    See the full U Michigan article here .


    five-ways-keep-your-child-safe-school-shootings


    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

    U MIchigan Campus

    The University of Michigan (U-M, UM, UMich, or U of M), frequently referred to simply as Michigan, is a public research university located in Ann Arbor, Michigan, United States. Originally, founded in 1817 in Detroit as the Catholepistemiad, or University of Michigania, 20 years before the Michigan Territory officially became a state, the University of Michigan is the state’s oldest university. The university moved to Ann Arbor in 1837 onto 40 acres (16 ha) of what is now known as Central Campus. Since its establishment in Ann Arbor, the university campus has expanded to include more than 584 major buildings with a combined area of more than 34 million gross square feet (781 acres or 3.16 km²), and has two satellite campuses located in Flint and Dearborn. The University was one of the founding members of the Association of American Universities.

    Considered one of the foremost research universities in the United States,[7] the university has very high research activity and its comprehensive graduate program offers doctoral degrees in the humanities, social sciences, and STEM fields (Science, Technology, Engineering and Mathematics) as well as professional degrees in business, medicine, law, pharmacy, nursing, social work and dentistry. Michigan’s body of living alumni (as of 2012) comprises more than 500,000. Besides academic life, Michigan’s athletic teams compete in Division I of the NCAA and are collectively known as the Wolverines. They are members of the Big Ten Conference.

     
  • richardmitnick 2:50 pm on May 30, 2018 Permalink | Reply
    Tags: , , , CfA, , X-Ray Binary Stars at the Galactic Center   

    From Harvard-Smithsonian Center for Astrophysics: “X-Ray Binary Stars at the Galactic Center” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    1
    The central few light-years of our Milky Way. This X-ray image by Chandra shows the locations of some of the X-ray emitting point sources, including X-ray binary stars (cyan circles). A new analysis of archival Chandra data reports the first convincing evidence for this predicted, dense cluster of black holes. Chandra X-Ray Observatory/NASA, Hailey et al. 2018

    NASA/Chandra X-ray Telescope

    The center of our Milky Way galaxy is about twenty-five thousand light years from Earth, in the direction of the constellation Sagittarius. At the core of the galaxy is a supermassive black hole with about four million solar-masses of material and around it, within a volume just a few light-years in radius, orbit hundreds of massive stars and probably hundreds of thousands of smaller, harder to detect stars. The whole region is invisible to us in optical light because of the extensive amounts of absorbing, intervening dust. Other wavelengths, however, including the infrared, radio, and energetic X-rays, can penetrate the veiling material and enable us to study this unique environment.

    The supermassive black hole at a galaxy’s center is expected gradually to accumulate many small, stellar-mass black holes around it. In the case of our own galaxy, as many as 20,000 black holes may have settled around the central few light-years. So far, however, no such density cusp has been reported. One of the best ways to look for such black holes is via binary stars in which one member is stellar-mass black hole, because accretion around the black hole would generate detectable X-rays.

    CfA astronomer Jaesub Hong was a member of a six-person team that used the Chandra X-ray Observatory to search for such binaries. They examined the equivalent of several weeks worth of archival Chandra observations obtained over twelve years, in an area corresponding to a volume that stretches to about sixty light-years from the galactic nucleus. In this region, thousands of X-ray point sources are seen, produced by a range of processes including hot gas, stellar atmospheres, binaries with white dwarf star members, neutron stars, and black holes. The innermost region itself, out to about twelve light-years, has hundreds of sources. (For comparison, the nearest star to the Sun is four light-years away.) The X-ray energies of the sources can be used to diagnose their character, but in this dense complex source confusion was a challenge. To minimize the confusion, the team focused on relatively bright sources, about one hundred of them, and also used simulations as a reality check. They found that twelve of the sources in the central dozen light-years had relatively “soft” X-ray spectra consistent with these sources being black-hole binaries. Although some alternative explanations cannot be ruled out (for example, a class of pulsars), the observed X-ray properties of these sources are the first strong evidence for the population of black hole binaries predicted to settle near the galactic center. The results suggest there are a larger number of (still undetected) isolated BHs present, and not least emphasize the complex and fascinating nature of this unique location in our galaxy.

    Science paper:
    A Density Cusp of Quiescent X-Ray Binaries in the Central Parsec of the Galaxy. Nature

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    stem

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 2:34 pm on May 30, 2018 Permalink | Reply
    Tags: , , , CfA, , , Does Some Dark Matter Carry an Electric Charge?, EDGES collaboration   

    From Harvard-Smithsonian Center for Astrophysics: “Does Some Dark Matter Carry an Electric Charge?” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    May 30, 2018

    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    1

    Astronomers have proposed a new model for the invisible material that makes up most of the matter in the Universe. They have studied whether a fraction of dark matter particles may have a tiny electrical charge.

    “You’ve heard of electric cars and e-books, but now we are talking about electric dark matter,” said Julian Munoz of Harvard University in Cambridge, Mass., who led the study that has been published in the journal Nature. “However, this electric charge is on the very smallest of scales.”

    Munoz and his collaborator, Avi Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., explore the possibility that these charged dark matter particles interact with normal matter by the electromagnetic force.

    Their new work dovetails with a recently announced result from the Experiment to Detect the Global EoR (Epoch of Reionization) Signature (EDGES) collaboration. In February, scientists from this project said they had detected the radio signature from the first generation of stars, and possible evidence for interaction between dark matter and normal matter. Some astronomers quickly challenged the EDGES claim. Meanwhile, Munoz and Loeb were already looking at the theoretical basis underlying it.

    “We’re able to tell a fundamental physics story with our research no matter how you interpret the EDGES result,” said Loeb, who is the chair of the Harvard astronomy department. “The nature of dark matter is one of the biggest mysteries in science and we need to use any related new data to tackle it.”

    The story begins with the first stars, which emitted ultraviolet (UV) light. According to the commonly accepted scenario, this UV light interacted with cold hydrogen atoms in gas lying between the stars and enabled them to absorb the cosmic microwave background (CMB) radiation, the leftover radiation from the Big Bang.

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    This absorption should have led to a drop in intensity of the CMB during this period, which occurs less than 200 million years after the Big Bang. The EDGES team claimed to detect evidence for this absorption of CMB light, though this has yet to be independently verified by other scientists. However, the temperature of the hydrogen gas in the EDGES data is about half of the expected value.

    “If EDGES has detected cooler than expected hydrogen gas during this period, what could explain it?” said Munoz. “One possibility is that hydrogen was cooled by the dark matter.”

    At the time when CMB radiation is being absorbed, the any free electrons or protons associated with ordinary matter would have been moving at their slowest possible speeds (since later on they were heated by X-rays from the first black holes). Scattering of charged particles is most effective at low speeds. Therefore, any interactions between normal matter and dark matter during this time would have been the strongest if some of the dark matter particles are charged. This interaction would cause the hydrogen gas to cool because the dark matter is cold, potentially leaving an observational signature like that claimed by the EDGES project.

    “We are constraining the possibility that dark matter particles carry a tiny electrical charge – equal to one millionth that of an electron – through measurable signals from the cosmic dawn,” said Loeb. “Such tiny charges are impossible to observe even with the largest particle accelerators.”

    Only small amounts of dark matter with weak electrical charge can both explain the EDGES data and avoid disagreement with other observations. If most of the dark matter is charged, then these particles would have been deflected away from regions close to the disk of our own Galaxy, and prevented from reentering. This conflicts with observations showing that large amounts of dark matter are located close to the disk of the Milky Way.

    Scientists know from observations of the CMB that protons and electrons combined in the early Universe to form neutral atoms. Only a small fraction of these charged particles, about one in a few thousand, remained free. Munoz and Loeb are considering the possibility that dark matter may have acted in a similar way. The data from EDGES, and similar experiments, might be the only way to detect the few remaining charged particles, as most of the dark matter would be neutral.

    “The viable parameter space for this scenario is quite constrained, but if confirmed by future observations, of course we would be learning something fundamental about the nature of dark matter, one of the biggest puzzles that we have in physics today,” said Harvard’s Cora Dvorkin who was not involved with the new study.

    Lincoln Greenhill also from the CfA is currently testing the observational claim by the EDGES team. He leads the Large Aperture Experiment to Detect the Dark Ages (LEDA) project, which uses the Long Wavelength Array in Owen’s Valley California and Socorro, New Mexico.

    A paper describing these results appear in the May 31, 2018 issue of the journal Nature.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    stem

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 3:36 pm on May 1, 2018 Permalink | Reply
    Tags: , , , CfA, , , , Greenland Telescpe achieves "first light" and more, ,   

    From Harvard Smithsonian Center for Astrophysics: “Greenland Telescope Opens New Era of Arctic Astronomy” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    May 1, 2018

    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    NSF CfA Greenland telescope

    NSF CfA Greenland telescope

    To study the most extreme objects in the Universe, astronomers sometimes have to go to some extreme places themselves. Over the past several months, a team of scientists has braved cold temperatures to put the finishing touches on a new telescope in Greenland. [This is a major gain for astronomy in the Northern Hemisphere, which sometimes seems to be less productive than the astronomical assets in the Southern Hemsphere.]

    Taking advantage of excellent atmospheric conditions, the Greenland Telescope is designed to detect radio waves from stars, galaxies and black holes. One of its primary goals is to join the Event Horizon Telescope (EHT), a global array of radio dishes that are linked together to make the first image of a supermassive black hole.

    Event Horizon Telescope Array

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM NOEMA interferometer
    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    NSF CfA Greenland telescope

    The Greenland Telescope has recently achieved two important milestones, its “first light” and the successful synchronization with data from another radio telescope. With this, the Greenland Telescope is ready to help scientists explore some of the Universe’s deepest mysteries.

    “We can officially announce that we are open for business to explore the cosmos from Greenland,” said Timothy Norton of the Harvard-Smithsonian Center for Astrophysics (CfA) and Senior Project Manager for the telescope. “It’s an exciting day for everyone who has worked so hard to make this happen.”

    In December 2017, astronomers were able to successfully detect radio emission from the Moon using the Greenland Telescope, an event astronomers refer to as “first light.” Then in early 2018, scientists combined data from the Greenland Telescope’s observations of a quasar with data from the Atacama Large Millimeter/submillimeter Array, or ALMA.

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

    The data from the Greenland Telescope and ALMA were synchronized so that they acted like two points on a radio dish equal in size to the separation of the two observing sites, an achievement that is called “finding fringes.”

    “This represents a major step in integrating the telescope into a larger, global network of radio telescopes,” said Nimesh Patel of CfA. “Finding fringes tells us that the Greenland Telescope is working as we hoped and planned.”

    The Greenland Telescope is a 12-meter radio antenna that was originally built as a prototype for ALMA. Once ALMA was operational in Chile, the telescope was repurposed to Greenland to take advantage of the near-ideal conditions of the Arctic to study the Universe at specific radio frequencies.

    The Greenland location also allows interferometry with the Submillimeter Array in Hawaii, ALMA and other radio dishes, to become a part of the northernmost component of the EHT. This extends the baseline of this array in the north-south direction to about 12,000 km (about 7,500 miles).

    CfA Submillimeter Array Mauna Kea, Hawaii, USA, Altitude 4,080 m (13,390 ft)

    “The EHT essentially turns the entire globe into one giant radio telescope, and the farther apart radio dishes in the array are, the sharper the images the EHT can make,” said Sheperd Doeleman of the CfA and leader of the EHT project. “The Greenland Telescope will help us obtain the best possible image of a supermassive black hole outside our galaxy.”

    The Greenland Telescope joined the EHT observing campaign in the middle of April 2018 to observe the supermassive black hole at the center of the galaxy M87. This supermassive black hole and the one in our galaxy are the two primary targets for the EHT, because the apparent sizes of their event horizons are larger than for any other black hole. Nevertheless exquisite telescope resolution is required, equivalent to reading a newspaper on the Moon. This capability is about a thousand times better than what the best optical telescopes in the world can achieve.

    Scientists plan to use these observations to help test Einstein’s theory of General Relativity in environments where extreme gravity exists, and probe the physics around black holes with unprecedented detail.

    In 2011, NSF, the Associated Universities, Inc. (AUI)/National Radio Astronomy Observatory (NRAO) awarded the antenna to the Smithsonian Astrophysical Observatory (SAO) for relocation to Greenland. SAO’s project partner, the Academia Sinica Institute of Astronomy & Astrophysics (ASIAA) of Taiwan, led the effort to refurbish and rebuild the antenna to prepare it for the cold climate of Greenland’s ice sheet. In 2016, the telescope was shipped to the Thule Air Base, Greenland, 750 miles inside the Arctic Circle, where it was reassembled at this sea-level coastal site. A future site is under consideration a the summit of the Greenland ice sheet where we will be able to take advantage of lower water vapor in the atmosphere overhead and achieve even better resolution at the higher operating frequencies.

    More information on the Greenland Telescope can be found at https://www.cfa.harvard.edu/greenland12m/

    Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 2:42 pm on April 28, 2018 Permalink | Reply
    Tags: , , , , CfA,   

    From Center For Astrophysics: “Finding Galaxies with Active Nuclei” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    1
    The Hubble image of a galaxy spotted by Spitzer’s IRAC infrared camera to be variable, probably because it harbors an active galactic nucleus. IRAC infrared surveys taken over a decade have spotted about 800 previously unknown AGN. NASA/Hubble; Polimera et al. 2018

    The nuclei of most galaxies host supermassive black holes with millions or even billions of solar-masses of material. Material in the vicinity of such black holes can accrete onto a torus of dust and gas around the black hole, and when that happens the nuclei radiate powerfully across the full spectrum. These active galactic nuclei (AGN) are among the most dramatic and interesting phenomena in extragalactic astronomy, and puzzling as well.

    1
    Inner Structure of an Active Galaxy. 8 February 2016. Author Original: Unknown; Vectorization: Wikipedia user-Rothwild

    Exactly what turns the accretion on or off is not understood, nor is how the associated processes produce the emission, generate jets of particles, or influence star formation in the galaxy.

    Because AGN play an important role in the evolution of galaxies, astronomers are studying galaxies with AGN at cosmological distances. It is in earlier epochs of the universe, about ten billion years after the big bang, when the most significant AGN fueling is thought to occur. But AGN at these distances are also faint and more difficult to find. Historically, they have been spotted by their having very red colors due to heavy dust obscuration, characteristic emission lines (signaling very hot gas), and/or their variability.

    CfA astronomers Matt Ashby, Steve Willner and Giovanni Fazio and two colleagues used deep infrared extragalactic surveys taken over 14 years by the IRAC instrument on the Spitzer Space Telescope to search for distant AGN. The various surveys in the archive repeatedly scanned different portions of the sky over as many as eleven epochs in their efforts to peer deeper and farther into the cosmos, and the multiple observations allow spotting variable sources. The astronomers found almost a thousand infrared-variable galaxies in these surveys, about one percent of all the galaxies recorded. They estimate that about eighty percent of these variable sources are AGN, the others being due either to supernovae or spurious data. The variability had not been seen in studies at other wavelengths because of the heavy obscuration around the nuclei and/or the weakness of X-ray emission; the infrared can peer through the obscuring dust. The team examined Hubble images of the sources and finds that a majority show indication of disruption, perhaps from a galaxy-galaxy collision. Their results suggest that mid-infrared variability identifies a unique population of galaxies with AGN.

    Science paper:
    Morphologies of mid-IR variability-selected AGN host galaxies . MNRAS

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 4:21 pm on April 12, 2018 Permalink | Reply
    Tags: , , , Cataclysmic variable stars (CVs) in the globular cluster 47 Tucanae, CfA, , Exotic Binary Stars   

    From CfA: “Exotic Binary Stars” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    1
    A Chandra X-ray Observatory image of the globular cluster 47 Tucanae. The image is about ten light-years across, and shows many cataclysmic variables (CVs), white dwarf stars that accrete from a companion star. Astronomers have discovered twenty-two new CVs in the cluster, and used the statistics to argue that, unlike many clusters which have bright, recently formed CVs, the ones here are older or even primordial.
    NASA/CXC/Michigan State/A.Steiner et al. 2014.

    NASA/Chandra Telescope

    Cataclysmic variable stars (CVs) are white dwarf stars that are accreting from an orbiting, low mass binary companion star. The accretion is facilitated by the proximity of the stars; typical orbital periods range from about one to ten hours. Although the family of these exotic CV binaries is heterogeneous, there are, roughly speaking, four classes characterized by the accretion physics, eruptions caused by occasional accretion events, flaring from activity on the white dwarf’s surface, and the appearance of hydrogen lines in the companion star.

    CVs are found in many galactic environments, but their presence in globular clusters, whose distances and populations are well characterized, allows a more precise comparative study of their properties. CVs can affect the evolution of the cluster while themselves being influenced by the dense stellar environment in a cluster. Evolutionary models of globular cluster evolution imply that after about ten billion years, a cluster with a million stars should have about two hundred CVs – many more than have been seen so far in any cluster. Identifying them, however, is not easy because they can be faint and because they exist in such crowded environments.

    CfA astronomers Maureen van den Berg and Josh Grindlay and their colleagues detected twenty-two new CVs in the nearby globular cluster 47 Tucanae (47 Tuc) using Chandra X-ray Observatory and Hubble measurements, bringing the total known to forty-three, the largest sample in any globular cluster so far.

    NASA/ESA Hubble Telescope

    The scientists find that 47 Tuc has fewer bright CVs than had been expected. Many globular clusters show a steep increase in stellar density near their centers (the so-called “core collapse” scenario). The scientists argue that the high central densities in these core-collapsed clusters has led to frequent close encounters between stars, which in turn has resulted in the formation of younger and brighter CVs. The cluster 47 Tuc has not experienced core collapse, which could explain the relative lack of such bright CVs. These new results imply that the CV population in 47 Tuc is therefore a combination of primordial CVs and others formed dynamically early in the evolution of the cluster.

    Science paper:
    New Cataclysmic Variables and Other Exotic Binaries in the Globular Cluster 47 Tucanae
    MNRAS

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: