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  • richardmitnick 8:26 am on November 1, 2014 Permalink | Reply
    Tags: , , , , , Royal Astronomical Society   

    From RAS: “When did galaxies settle down?” 

    Royal Astronomical Society

    Royal Astronomical Society

    30 October 2014
    Media contact
    Dr Robert Massey
    Royal Astronomical Society
    Tel: +44 (0)20 7734 3307 / 4582
    Mob: +44 (0)794 124 8035
    rm@ras.org.uk

    Science contact
    Dr Brooke Simmons
    University of Oxford
    Tel: +44 (0)1865 273637
    brooke.simmons@astro.ox.ac.uk

    Astronomers have long sought to understand exactly how the universe evolved from its earliest history to the cosmos we see around us in the present day. In particular, the way that galaxies form and develop is still a matter for debate. Now a group of researchers have used the collective efforts of the hundreds of thousands of people that volunteer for the Galaxy Zoo project to shed some light on this problem. They find that galaxies may have settled into their current form some two billion years earlier than previously thought.

    gz
    A Hubble Space Telescope image of a spiral galaxy seen when the Universe was less than a third of its current age, yet showing the same barred feature as much older, settled disk galaxies. Credit: NASA, ESA, J. Kartaltepe (NOAO), C. Lintott (Oxford), H. Ferguson (STScI), S. Faber (UCO).

    Dr Brooke Simmons of the University of Oxford and her collaborators describe the work in a paper in Monthly Notices of the Royal Astronomical Society. The team set Zoo volunteers the task of classifying the shapes of tens of thousands of galaxies observed by the Hubble Space Telescope. These objects are typically very distant, so we see them as they appeared more than 10 billion years ago, when the universe was about 3 billion years old, less than a quarter of its present age.

    NASA Hubble Telescope
    NASA Hubble schematic
    NASA/ESA Hubble

    The newly classified galaxies are striking in that they look a lot like those in today’s universe, with disks, bars and spiral arms. But theorists predict that these should have taken another 2 billion years to begin to form, so things seem to have been settling down a lot earlier than expected.

    ngc
    A European Southern Observatory image of the barred spiral galaxy NGC 1365, rotated to match the orientation of the first image. NGC 1365 is about 56 million light years away, so we see it as it appears 56 million years ago, or 10 billion years later than the galaxy in the HST image. Credit: ESO/IDA/Danish 1.5 m/ R. Gendler, J-E. Ovaldsen, C. Thöne, and C. Feron. Brooke comments: “When we started looking for these galaxies, we didn’t really know what we’d find. We had predictions from galaxy simulations that we shouldn’t find any of the barred features that we see in nearby, evolved galaxies, because very young galaxies might be too agitated for them to form.”

    ‘But we now know that isn’t the case. With the public helping us search through many thousands of images of distant galaxies, we discovered that some galaxies settle very early on in the Universe.”

    See the full article here.

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

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  • richardmitnick 4:45 pm on September 22, 2014 Permalink | Reply
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    From RAS: “Finding hints of gravitational waves in the stars” 

    Royal Astronomical Society

    Royal Astronomical Society

    September 22, 2014

    Media contact

    Kendra Snyder
    Manager of Science Communication
    Department of Communications
    American Museum of Natural History
    New York
    USA
    Tel: +1 212 496 3419
    ksnyder@amnh.org

    Science contacts

    Prof Barry L McKernan
    Department of Astrophysics
    American Museum of Natural History
    New York
    USA
    bmckernan@amnh.org

    Saavik K Ford
    Associate Professor
    American Museum of Natural History
    New York
    USA
    sford@amnh.org
    Scientists have shown how gravitational waves—invisible ripples in the fabric of space and time that propagate through the universe—might be “seen” by looking at the stars. The new model proposes that a star that oscillates at the same frequency as a gravitational wave will absorb energy from that wave and brighten, an overlooked prediction of [Albert] Einstein’s 1916 theory of general relativity. The study, which was published today in the journal Monthly Notices of the Royal Astronomical Society: Letters, contradicts previous assumptions about the behaviour of gravitational waves.

    “It’s pretty cool that a hundred years after Einstein proposed this theory, we’re still finding hidden gems,” said Barry McKernan, a research associate in the American Museum of Natural History’s Department of Astrophysics, who is also a professor at CUNY’s Borough of Manhattan Community College; a faculty member at CUNY’s Graduate Center; and a Kavli Scholar at the Kavli Institute for Theoretical Physics.

    Gravitational waves can be thought of like the sound waves emitted after an earthquake, but the source of the “tremors” in space are energetic events like supernovae (exploding stars), binary neutron stars (pairs of burned-out cores left behind when stars explode), or the mergers of black holes and neutron stars. Although scientists have long known about the existence of gravitational waves, they’ve never made direct observations but are attempting to do so through experiments on the ground and in space.

    gw
    An illustration of the gravitational waves generated by two black holes in orbit around one other. Credit: NASA. Part of the reason why detection is difficult is because the waves interact so weakly with matter. But McKernan and his colleagues from CUNY, the Harvard-Smithsonian Center for Astrophysics, the Institute for Advanced Study, and Columbia University, suggest that gravitational waves could have more of an effect on matter than previously thought.

    The new model shows that stars with oscillations—vibrations—that match the frequency of gravitational waves passing through them can resonate and absorb a large amount of energy from the ripples.

    “It’s like if you have a spring that’s vibrating at a particular frequency and you hit it at the same frequency, you’ll make the oscillation stronger,” McKernan said. “The same thing applies with gravitational waves.”

    If these stars absorb a large pulse of energy, they can be “pumped up” temporarily and made brighter than normal while they discharge the energy over time. This could provide scientists with another way to detect gravitational waves indirectly.

    “You can think of stars as bars on a xylophone—they all have a different natural oscillation frequency,” said co-author Saavik Ford, who is a research associate in the Museum’s Department of Astrophysics as well as a professor at the Borough of Manhattan Community College, CUNY; a faculty member at CUNY’s Graduate Center; and a Kavli Scholar at the Kavli Institute for Theoretical Physics.

    ‘If you have two black holes merging with each other and emitting gravitational waves at a certain frequency, you’re only going to hit one of the bars on the xylophone at a time. But because the black holes decay as they come closer together, the frequency of the gravitational waves changes and you’ll hit a sequence of notes. So you’ll likely see the big stars lighting up first followed by smaller and smaller ones.”

    The work also presents a different way to indirectly detect gravitational waves. From the perspective of a gravitational wave detector on Earth or in space, when a star at the right frequency passes in front of an energetic source such as merging black holes, the detector will see a drop in the intensity of gravitational waves measured. In other words, stars—including our own Sun—can eclipse background sources of gravitational waves.

    “You usually think of stars as being eclipsed by something, not the other way around,” McKernan said.

    The researchers will continue to study these predictions and try to determine how long it would take to observe these effects from a telescope or detector.

    See the full article here.

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

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    See the full article here.

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  • richardmitnick 8:22 am on September 19, 2014 Permalink | Reply
    Tags: , , , , Galaxy Formation, Royal Astronomical Society   

    From RAS: “Monster galaxies gain weight by eating smaller neighbours” 

    Royal Astronomical Society

    Royal Astronomical Society

    Friday, 19 September 2014
    Media contact

    Kirsten Gottschalk
    Media Contact, ICRAR (Perth, GMT +8:00)
    Tel: +61 8 6488 7771
    Mob: +61 438 361 876
    kirsten.gottschalk@icrar.org

    University of Western Australia Media Office
    Tel: +61 8 6488 7977

    Science contacts

    Dr Aaron Robotham
    ICRAR – UWA (Currently travelling in South Africa, GMT +2:00)
    aaron.robotham@icrar.org

    Professor Simon Driver
    Principal Investigator of the GAMA project
    ICRAR – UWA (Perth, GMT +8:00)
    Tel: +61 8 6488 7747
    simon.driver@icrar.org

    Massive galaxies in the Universe have stopped making their own stars and are instead snacking on nearby galaxies, according to research by Australian scientists. They publish their results in the journal Monthly Notices of the Royal Astronomical Society.

    Astronomers looked at more than 22,000 galaxies and found that while smaller galaxies are very efficient at creating stars from gas, the most massive galaxies are much less efficient at star formation, producing hardly any new stars themselves, and instead grow by eating other galaxies.

    Dr Aaron Robotham, who is based at the University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), said smaller ‘dwarf’ galaxies were being eaten by their larger counterparts.

    “All galaxies start off small and grow by collecting gas and quite efficiently turning it into stars,” he said.

    “Then every now and then they get completely cannibalised by some much larger galaxy.”

    many
    Some of the many thousands of merging galaxies identified within the GAMA survey. Credit: Professor Simon Driver and Dr Aaron Robotham, ICRAR. Dr Robotham, who led the research, said our own Milky Way is at a tipping point and is expected to now grow mainly by eating smaller galaxies, rather than by collecting gas.

    “The Milky Way hasn’t merged with another large galaxy for a long time but you can still see remnants of all the old galaxies we’ve cannibalised” he said.

    “We’re also going to eat two nearby dwarf galaxies, the Large and Small Magellanic Clouds, in about four billion years.”

    smc
    The two-color image shows an overview of the full Small Magellanic Cloud (SMC) and was composed from two images from the Digitized Sky Survey 2. The field of view is slightly larger than 3.5 × 3.6 degrees. N66 with the open star cluster NGC 346 is the largest of the star-forming regions seen below the center of the SMC.
    Date 10 November 2005
    Source http://www.spacetelescope.org/images/html/heic0514c.html (direct link)
    Author NASA/ESA Hubble and Digitized Sky Survey 2

    lmc
    Large Magellanic Cloud
    No text

    NASA Hubble Telescope
    NASA/ESA Hubble

    Sloan Digital Sky Survey Telescope
    Sloan Digital Sky Survey Telescope at Apache Point

    But Dr Robotham said the Milky Way is eventually going to get its comeuppance when it merges with the nearby Andromeda Galaxy in about five billion years.

    andro
    Andromeda Galaxy
    The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years away in the constellation Andromeda. The image also shows Messier Objects 32 and 110, as well as NGC 206 (a bright star cloud in the Andromeda Galaxy) and the star Nu Andromedae. This image was taken using a hydrogen-alpha filter.
    18 September 2010, Adam Evans

    “Technically, Andromeda will eat us because it’s the more massive one” he said.

    Almost all of the data for the research was collected with the Anglo-Australian Telescope in New South Wales as part of the Galaxy And Mass Assembly (GAMA) survey, which is led by Professor Simon Driver at ICRAR.

    aat
    aai
    Anglo-Australian Telescope

    The GAMA survey involves more than 90 scientists and took seven years to complete. This study is one of over 60 publications to have come from the work, with another 180 currently in progress.

    Dr Robotham said as galaxies grow, they have a stronger gravitational field and can therefore more easily pull in their neighbours. He said the reason star formation slows down in really massive galaxies is thought to be because of extreme feedback events in a very bright region at the centre of a galaxy known as an active galactic nucleus.

    “The topic is much debated, but a popular mechanism is where the active galactic nucleus basically cooks the gas and prevents it from cooling down to form stars,” Dr Robotham said.

    Ultimately, gravity is expected to cause all the galaxies in bound groups and clusters to merge into a few super-giant galaxies, although we will have to wait many billions of years before that happens.

    “If you waited a really, really, really long time that would eventually happen, but by really long I mean many times the age of the Universe so far,” Dr Robotham explained.

    See the full article here.

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

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  • richardmitnick 11:14 am on September 16, 2014 Permalink | Reply
    Tags: , , , , , Royal Astronomical Society   

    From RAS: “219 million stars: a detailed catalogue of the visible Milky Way” 

    Royal Astronomical Society

    Royal Astronomical Society

    16 September 2014
    Media contact

    Dr Robert Massey
    Royal Astronomical Society
    Tel: +44 (0)20 7734 3307
    Mob: +44 (0)794 124 8035
    rm@ras.org.uk

    Science contacts

    Dr Geert Barentsen
    University of Hertfordshire
    Tel: +44 (0)1707 284603
    g.barentsen@herts.ac.uk

    Prof. Janet Drew
    University of Hertfordshire
    Tel: +44 (0)1707 286576
    j.drew@herts.ac.uk

    A new catalogue of the visible part of the northern part of our home Galaxy, the Milky Way, includes no fewer than 219 million stars. Geert Barentsen of the University of Hertfordshire led a team who assembled the catalogue in a ten year programme using the Isaac Newton Telescope (INT) on La Palma in the Canary Islands. Their work appears today in the journal Monthly Notices of the Royal Astronomical Society.

    Isaac Newton 2.5m telescope
    Isaac Newton 2.5m telescope interior
    Isaac Newton Telescope

    dense
    A density map of part of the Milky Way disk, constructed from IPHAS data. The axes show galactic latitude and longitude, coordinates that relate to the position of the centre of the galaxy. The mapped data are the counts of stars detected in i, the longer (redder) wavelength broad band of the survey, down to a faint limit of 19th magnitude. Although this is just a small section of the full map, it portrays in exquisite detail the complex patterns of obscuration due to interstellar dust. Credit: Hywel Farnhill, University of Hertfordshire.

    From dark sky sites on Earth, the Milky Way appears as a glowing band stretching across the sky. To astronomers, it is the disk of our own galaxy, a system stretching across 100,000 light-years, seen edge-on from our vantage point orbiting the Sun. The disk contains the majority of the stars in the galaxy, including the Sun, and the densest concentrations of dust and gas.

    The unaided human eye struggles to distinguish individual objects in this crowded region of the sky, but the 2.5-metre mirror of the INT enabled the scientists to resolve and chart 219 million separate stars. The INT programme charted all the stars brighter than 20th magnitude – or 1 million times fainter than can be seen with the human eye.

    Using the catalogue, the scientists have put together an extraordinarily detailed map of the disk of the Galaxy that shows how the density of stars varies, giving them a new and vivid insight into the structure of this vast system of stars, gas and dust.

    The image included here, a cut-out from a stellar density map mined directly from the released catalogue, illustrates the new view obtained. The Turner-like brush strokes of dust shadows would grace the wall of any art gallery. Maps like these also stand as useful tests of new-generation models for the Milky Way.

    The production of the catalogue, IPHAS DR2 (the second data release from the survey programme The INT Photometric H-alpha Survey of the Northern Galactic Plane, IPHAS), is an example of modern astronomy’s exploitation of ‘big data’. It contains information on 219 million detected objects, each of which is summarised in 99 different attributes.

    With this catalogue release, the team are offering the world community free access to measurements taken through two broad band filters capturing light at the red end of the visible spectrum, and in a narrow band capturing the brightest hydrogen emission line, H-alpha. The inclusion of H-alpha also enables exquisite imaging of the nebulae (glowing clouds of gas) found in greatest number within the disk of the Milky Way. The stellar density map illustrated here is derived from the longest (reddest) wavelength band in which the darkening effect of the dust is moderated in a way that brings out more of its structural detail, compared to maps built at shorter (bluer) wavelengths.

    See the full article here.

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

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  • richardmitnick 7:02 am on September 9, 2014 Permalink | Reply
    Tags: , , , , , Royal Astronomical Society   

    From The Royal Astronomical Society: “Interactive dark matter could explain Milky Way’s missing satellite galaxies” 

    Royal Astronomical Society

    Royal Astronomical Society

    Tuesday, 09 September 2014
    Media contacts

    Durham University Media Relations Team
    Tel: +44 (0)191 334 6075
    media.relations@durham.ac.uk

    Dr Robert Massey
    Royal Astronomical Society
    Tel: +44 (0)20 7734 3307 x214
    Mob: +44 (0)794 124 8035
    rm@ras.org.uk

    Science contacts

    All the contacts are available for interview on Monday 8 and Tuesday 9 September.

    Professor Carlton Baugh
    Institute for Computational Cosmology
    Durham University
    Tel: +44 (0)191 33 43542
    c.m.baugh@durham.ac.uk

    Ryan Wilkinson
    Institute for Computational Cosmology
    Durham University
    Tel: +44 (0)191 33 45753
    ryan.wilkinson@durham.ac.uk

    Jascha Schewtschenko
    Institute for Computational Cosmology
    Durham University
    Tel: +44 (0)191 33 43710
    j.a.schewtschenko@durham.ac.uk

    Scientists believe they have found a way to explain why there are not as many galaxies orbiting the Milky Way as expected. Computer simulations of the formation of our galaxy suggest that there should be many more small galaxies around the Milky Way than are observed through telescopes.

    This has thrown doubt on the generally accepted theory of cold dark matter, an invisible and mysterious substance that scientists predict should allow for more galaxy formation around the Milky Way than is seen.

    sim
    The simulated distribution of dark matter in a Milky Way-like galaxy for standard, non-interacting dark matter (top left), warm dark matter (top right) and the new dark matter model that interacts with the photon background (bottom). Smaller structures are erased up to the point where, in the most extreme model (bottom right), the galaxy is completely sterilised. Credit: Durham University. Now cosmologists and particle physicists at the Institute for Computational Cosmology and the Institute for Particle Physics Phenomenology, at Durham University, working with colleagues at LAPTh College & University in France, think they have found a potential solution to the problem.

    Writing in the journal Monthly Notices of the Royal Astronomical Society, the scientists suggest that dark matter particles, as well as feeling the force of gravity, could have interacted with photons and neutrinos in the young Universe, causing the dark matter to scatter.

    Scientists think clumps of dark matter – or haloes – that emerged from the early Universe, trapped the intergalactic gas needed to form stars and galaxies. Scattering the dark matter particles wipes out the structures that can trap gas, stopping more galaxies from forming around the Milky Way and reducing the number that should exist.

    Lead author Dr Celine Boehm, in the Institute for Particle Physics Phenomenology at Durham University, said: “We don’t know how strong these interactions should be, so this is where our simulations come in.”

    “By tuning the strength of the scattering of particles, we change the number of small galaxies, which lets us learn more about the physics of dark matter and how it might interact with other particles in the Universe.”

    “This is an example of how a cosmological measurement, in this case the number of galaxies orbiting the Milky Way, is affected by the microscopic scales of particle physics.”

    There are several theories about why there are not more galaxies orbiting the Milky Way, which include the idea that heat from the Universe’s first stars sterilised the gas needed to form stars. The researchers say their current findings offer an alternative theory and could provide a novel technique to probe interactions between other particles and cold dark matter.

    two
    Two models of the dark matter distribution in the halo of a galaxy like the Milky Way, separated by the white line. The colours represent the density of dark matter, with red indicating high-density and blue indicating low-density. On the left is a simulation of how non-interacting cold dark matter produces an abundance of smaller satellite galaxies. On the right the simulation shows the situation when the interaction of dark matter with other particles reduces the number of satellite galaxies we expect to observe around the Milky Way. Credit: Durham University.

    Co-author Professor Carlton Baugh said: “Astronomers have long since reached the conclusion that most of the matter in the Universe consists of elementary particles known as dark matter.”

    “This model can explain how most of the Universe looks, except in our own backyard where it fails miserably.”

    “The model predicts that there should be many more small satellite galaxies around our Milky Way than we can observe.”

    “However, by using computer simulations to allow the dark matter to become a little more interactive with the rest of the material in the Universe, such as photons, we can give our cosmic neighbourhood a makeover and we see a remarkable reduction in the number of galaxies around us compared with what we originally thought.”

    The calculations were carried out using the COSMA supercomputer at Durham University, which is part of the UK-wide DiRAC super-computing framework.

    The work was funded by the Science and Technology Facilities Council and the European Union.

    See the full article here.

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

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  • richardmitnick 6:14 pm on August 12, 2014 Permalink | Reply
    Tags: , , , , Royal Astronomical Society,   

    From The Royal Astronomical Society: “NASA’s NuSTAR sees rare blurring of black hole light” 

    Royal Astronomical Society

    Royal Astronomical Society

    12 August 2014
    J.D. Harrington
    Headquarters, Washington
    202-358-5241
    j.d.harrington@nasa.gov

    Whitney Clavin
    Jet Propulsion Laboratory
    Pasadena
    California
    United States
    Tel: +1 818 354 4673
    whitney.clavin@jpl.nasa.gov

    Science contact

    Prof Michael Parker
    Institute of Astronomy
    Cambridge
    United Kingdom
    Tel: +44 (0)1223 337 511
    mlparker@ast.cam.ac.uk

    Scientists have used NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), an orbiting X-ray telescope, to capture an extreme and rare event in the regions immediately surrounding a supermassive black hole. A compact source of X-rays that sits near the black hole, called the corona, has moved closer to the black hole over a period of just days. The researchers publish their results in Monthly Notices of the Royal Astronomical Society.

    NASA NuSTAR
    NASA/NuSTAR

    smbh
    An artist’s impression of a supermassive black hole and its surroundings. The regions around supermassive black holes shine brightly in X-rays. Some of this radiation comes from a surrounding disk, and most comes from the corona, pictured here as the white light at the base of a jet. This is one possible configuration for the Mrk 335 corona, as its actual shape is unclear. Credit: NASA-JPL / Caltech.

    “The corona recently collapsed in towards the black hole, with the result that the black hole’s intense gravity pulled all the light down onto its surrounding disk, where material is spiralling inward,” said Michael Parker of the Institute of Astronomy in Cambridge, lead author of the new paper.

    As the corona shifted closer to the black hole, the black hole’s gravitational field exerted a stronger tug on the x-rays emitted by the corona. The result was an extreme blurring and stretching of the X-ray light. Such events had been observed previously, but never to this degree and in such detail.

    Supermassive black holes are thought to reside in the centres of all galaxies. Some are more massive and rotate faster than others. The black hole in this new study, referred to as Markarian 335, or Mrk 335, is about 324 million light-years from Earth in the direction of the Pegasus constellation. It is one of the most extreme systems of which the mass and spin rate have ever been measured. The black hole squeezes about 10 million times the mass of our Sun into a region only 30 times as wide as the Sun’s diameter, and it spins so rapidly that space and time are dragged around with it.

    Even though some light falls into a supermassive black hole never to be seen again, other high-energy light emanates from both the corona and the surrounding accretion disk of superheated material. Though astronomers are uncertain of the shape and temperature of coronas, they know that they contain particles that move close to the speed of light.

    NASA’s Swift satellite has monitored Mrk 335 for years, and recently noted a dramatic change in its X-ray brightness. In what is called a ‘target-of-opportunity’ observation, NuSTAR was redirected to take a look at high-energy X-rays from this source in the range of 3 to 79 kiloelectron volts. This particular energy range offers astronomers a detailed look at what is happening near the event horizon, the region around a black hole from which light can no longer escape gravity’s grasp.

    NASA SWIFT Telescope
    NASA/SWIFT

    Follow-up observations indicate that the corona still is in this close configuration, months after it moved. Researchers don’t know whether and when the corona will shift back. What is more, the NuSTAR observations reveal that the grip of the black hole’s gravity pulled the corona’s light onto the inner portion of its superheated disk, better illuminating it. The shifting corona lit up the precise region they wanted to study, almost as if somebody had shone a flashlight for the astronomers.

    The new data could ultimately help determine more about the mysterious nature of black hole coronas. In addition, the observations have provided better measurements of Mrk 335’s furious relativistic spin rate. Relativistic speeds are those approaching the speed of light, as described by Albert Einstein’s theory of relativity.

    “We still don’t understand exactly how the corona is produced or why it changes its shape, but we see it lighting up material around the black hole, enabling us to study the regions so close in that effects described by Einstein’s theory of general relativity become prominent,” said NuSTAR Principal Investigator Fiona Harrison of the California Institute of Technology (Caltech) in Pasadena. “NuSTAR’s unprecedented capability for observing this and similar events allows us to study the most extreme light-bending effects of general relativity.”

    See the full article here.

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

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  • richardmitnick 8:35 am on August 8, 2014 Permalink | Reply
    Tags: , , , , Royal Astronomical Society,   

    From Royal Astronomical Society: “White dwarfs crashing into neutron stars explain the loneliest supernovae “ 

    Royal Astronomical Society

    Royal Astronomical Society

    08 August 2014
    Tom Frew
    International Press Officer
    University of Warwick
    Tel: +44 (0)24 765 75910
    a.t.frew@warwick.ac.uk

    Dr Robert Massey
    Royal Astronomical Society
    Tel: +44 (0)20 7734 3307 / 4582
    Mob: +44 (0)794 124 8035
    rm@ras.org.uk

    Science contact

    Dr Joseph Lyman
    Department of Physics
    University of Warwick
    J.D.Lyman@warwick.ac.uk

    A research team led by astronomers and astrophysicists at the University of Warwick have found that some of the Universe’s loneliest supernovae are likely created by the collisions of white dwarf stars into neutron stars. Dr Joseph Lyman from the University of Warwick is the lead researcher on the paper, which is published in the journal Monthly Notices of the Royal Astronomical Society.

    syar
    An artist’s illustration of a white dwarf star (the stretched object right of centre) being dragged on to a neutron star (bottom centre). At the top left is the galaxy where the pair originated and other more distant galaxies can be seen elsewhere in the image. Credit: (c) Mark A. Garlick / space-art.co.uk / University of Warwick.

    Previous studies had shown that calcium comprised up to half of the material thrown off in such explosions compared to only a tiny fraction in normal supernovae. This means that these curious events may actually be the dominant producers of calcium in our universe.

    “One of the weirdest aspects is that they seem to explode in unusual places. For example, if you look at a galaxy, you expect any explosions to roughly be in line with the underlying light you see from that galaxy, since that is where the stars are” comments Dr Lyman. “However, a large fraction of these are exploding at huge distances from their galaxies, where the number of stellar systems is miniscule.

    “What we address in the paper is whether there are any systems underneath where these transients have exploded, for example there could be very faint dwarf galaxies there, explaining the weird locations. We present observations, going just about as faint as you can go, to show there is in fact nothing at the location of these transients – so the question becomes, how did they get there?”

    Calcium-rich transients observed to date can be seen tens of thousands of parsecs away from any potential host galaxy, with a third of these events at least 65 thousand light years from a potential host galaxy.

    The researchers used the Very Large Telescope in Chile and Hubble Space Telescope observations of the nearest examples of these calcium rich transients to attempt to detect anything left behind or in the surrounding area of the explosion.

    ESO VLT Interferometer
    ESO/VLT

    NASA Hubble Telescope
    NASA/ESA Hubble Telescope

    The deep observations taken allowed them to rule out the presence of faint dwarf galaxies or globular star clusters at the locations of these nearest examples. Furthermore, an explanation for core-collapse supernovae, which calcium-rich transients resemble, although fainter, is the collapse of a massive star in a binary system where material is stripped from the massive star undergoing collapse. The researchers found no evidence for a surviving binary companion or other massive stars in the vicinity, allowing them to reject massive stars as the progenitors of calcium rich transients.

    Professor Andrew Levan from the University of Warwick’s Department of Physics and a researcher on the paper said: “It was increasingly looking like hypervelocity massive stars could not explain the locations of these supernovae. They must be lower mass longer lived stars, but still in some sort of binary systems as there is no known way that a single low mass star can go supernova by itself, or create an event that would look like a supernova.”

    The researchers then compared their data to what is known about short-duration gamma ray bursts (SGRBs). These are also often seen to explode in remote locations with no coincident galaxy detected. SGRBs are understood to occur when two neutron stars collide, or when a neutron star merges with a black hole – this has been backed up by the detection of a ‘kilonova‘ accompanying a SGRB thanks to work led by Professor Nial Tanvir, a collaborator on this study.

    Although neutron star and black hole mergers would not explain these brighter calcium rich transients, the research team considered that if the collision was instead between a white dwarf star and neutron star, it would fit their observations and analysis because:

    It would provide enough energy to generate the luminosity of calcium rich transients.
    The presence of a white dwarf would provide a mechanism to produce calcium rich material.
    The presence of the Neutron star could explain why this binary star system was found so far from a host galaxy.

    Dr Lyman said: “What we therefore propose is these are systems that have been ejected from their galaxy. A good candidate in this scenario is a white dwarf and a neutron star in a binary system. The neutron star is formed when a massive star goes supernova. The supernova explosion causes the neutron star to be ‘kicked’ to very high velocities (100s of km/s). This high velocity system can then escape its galaxy, and if the binary system survives the kick, the white dwarf and neutron star will later merge, causing the explosive transient.”

    The researchers note that such merging systems of white dwarfs and neutron stars are postulated to produce high energy gamma-ray bursts, motivating further observations of any new examples of calcium rich transients to confirm this. Additionally, such merging systems will contribute significant sources of gravitational waves, potentially detectable by upcoming experiments that will shed further light on the nature of these exotic systems.

    See the full article here.

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

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