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  • richardmitnick 8:51 am on May 22, 2015 Permalink | Reply
    Tags: , , , Supernovas   

    From ANU: “Supernova ignition surprises scientists” 

    ANU Australian National University Bloc

    Australian National University

    21 May 2015
    No Writer Credit

    1
    NEWS from the Australian Gemini Office! ANU astronomer Dr Brad Tucker and his team used the Kepler Space Telescope together with the Gemini 8m telescope to catch supernovae in the act.

    Gemini South telescope
    Gemini South Interior
    Gemini

    Photo: Supernova SN2012fr, just to the left of the centre of the galaxy, outshone the rest of the galaxy for several weeks: Credit Brad Tucker and Emma Kirby

    Scientists have captured the early death throes of supernovae for the first time and found that the universe’s benchmark explosions are much more varied than expected.

    The scientists used the Kepler space telescope to photograph three type 1a supernovae in the earliest stages of ignition.

    NASA Kepler Telescope
    NASA/Kepler

    They then tracked the explosions in detail to full brightness around three weeks later, and the subsequent decline over the next few months.

    They found the initial stages of a supernova explosion did not fit with the existing theories.

    “The stars all blow up uniquely. It doesn’t make sense,” said Dr Brad Tucker, from the Research School of Astronomy and Astrophysics.

    “It’s particularly weird for these supernovae because even though their initial shockwaves are very different, they end up doing the same thing.”

    Before this study, the earliest type 1a supernovae had been glimpsed was more than 2.5 hours after ignition, after which the explosions all followed an identical pattern.

    This led astronomers to theorise that supernovae, the brilliant explosions of dying stars, all occurred through an identical process.

    Astronomers had thought supernovae all happened when a dense star steadily sucked in material from a large nearby neighbour until it became so dense that carbon in the star’s core ignited.

    “Somewhat to our surprise the results suggest an alternative hypothesis, that a violent collision between two smallish white dwarf stars sets off the explosion,” said lead researcher Dr Robert Olling, from the University of Maryland in the United States.

    At the peak of their brightness, supernovae are brighter than the billions of stars in their galaxy. Because of their brightness, astronomers have been able to use them to calculate distances to distant galaxies.

    Measurements of distant supernovae led to the discovery that some unknown force, now called dark energy, is causing the accelerated expansion of the universe. Brian Schmidt from the ANU, Saul Perlmutter (Berkeley) and Adam Reiss (Johns Hopkins) were awarded the Nobel prize in 2011 for this discovery.

    Dr Tucker said the new results did not undermine the discovery of dark energy.

    “The accelerating universe will not now go away – they will not have to give back their Nobel prizes,” he said.

    “The new results will actually help us to better understand the physics of supernovae, and figure out what is this dark energy that is dominating the universe.”

    The findings are published in Nature.

    See the full article here.

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    ANU Campus

    ANU is a world-leading university in Australia’s capital city, Canberra. Our location points to our unique history, ties to the Australian Government and special standing as a resource for the Australian people.

    Our focus on research as an asset, and an approach to education, ensures our graduates are in demand the world-over for their abilities to understand, and apply vision and creativity to addressing complex contemporary challenges.

     
  • richardmitnick 3:58 pm on May 20, 2015 Permalink | Reply
    Tags: , , , Supernovas   

    From Carnegie: “Strong UV Pulse Reveals Supernova’s Origin Story” 

    Carnegie Institution for Science
    Carnegie Institution for Science

    May 20, 2015
    No Writer Credit

    1
    An image from a simulation in which a type Ia supernova explodes (as shown in brown). The supernova material is ejected outward at a velocity of about 10,000 kilometers per second and slams into its companion star (as shown in light blue). The collision produces an ultraviolet pulse, which is emitted from the conical hole carved out by the companion star. Image is courtesy of Dan Kasen of University of California Berkeley.

    Type Ia supernovae are violent stellar explosions that shine as some of the brightest objects in the universe. But there are still many mysteries surrounding their origin—what kind of star system they originate in and how the explosions begin. New work from the intermediate Palomar Transient Factory team of astronomers, including Carnegie’s Mansi Kasliwal, provides strong evidence pointing toward one origin theory, called the single degenerate channel. This work is published May 21 by Nature.

    Type Ia supernovae are commonly theorized to be the thermonuclear explosions of a white dwarf star that is part of a binary system—two stars that are physically close and orbit around a common center of mass. But how this white dwarf goes from binary star system to type Ia supernova is a matter of debate.

    The single degenerate channel theory hypothesizes that the white dwarf accretes matter from its companion star and the resulting increase in its central pressure and temperature reaches a tipping point and ignites a thermonuclear explosion. In contrast, the double degenerate theory proposes that the orbit between two white dwarf stars shrinks until the lighter star’s path is disrupted and it moves close enough for some of its matter to be absorbed into the primary white dwarf and initiate an explosion.

    Last May, the iPTF team observed an explosion in the vicinity of a galaxy called IC 831, where no such activity had been seen previously, even the very night before. They called it iPTF14atg. Follow-up observations confirmed that this was indeed a type Ia supernova, one which ignited between May 2 and May 3.

    Looking at the event from Swift space telescope observation records, the team detected bright ultraviolet emission from the new supernova.

    NASA SWIFT Telescope
    NASA/Swift

    “I was examining the first Swift images when suddenly I saw a bright spot at the location of the supernova in the ultraviolet. I jumped up because I knew it was the signature that I had been hoping for,” said Caltech graduate student Yi Cao, lead author of the paper.

    Because ultraviolet radiation is higher energy than visible light, it is particularly suited to observing very hot objects like supernovae. Such an early UV pulse within days of a supernova’s explosion is unprecedented. This strong pulse of emission is consistent with theoretical expectations of collision between material being ejected from a supernova explosion and the companion star from which it has been accreting matter.

    “This provides good evidence that at least some type Ia supernovae arise from the single degenerate channel,” Kasliwal said. “Now we have to determine the fraction of Type Ia that are akin to iPTF14atg.”

    They sought a better understanding of the newly discovered supernova, and particularly of the UV pulse, comparing it to known supernovae in the type Ia family. Their spectroscopic findings with the Apache Point, Gemini, Palomar 200-inch, Nordic Optical Telescope, and Keck observatories indicate that iPTF14atg is a low-velocity type Ia. The team thinks it is likely other low-velocity type Ia supernovae also arose from the single degenerate channel. However, there are other higher-velocity Ia supernovae that likely originate from the double degenerate pathway, as other studies have indicated.

    Apache Point Observatory
    Apache Point Observatory interior
    Apache Point Observatory

    Gemini North telescope
    Gemini North Interior
    Gemini Observatory

    Caltech Palomar 200 inch Hale Telescope
    Caltech Palomar 200 inch Hale Telescope interior
    Palomar 200 inch Telescope

    Nordic Optical Telescope
    Nordic Opitcal Telescope Interior
    Nordic Optical Telescope

    Keck Observatory
    Keck Observatory Interior
    Keck Observatory

    The team’s findings indicate that UV observations of young supernovae could hold the key to fully understanding the pre-explosion interaction between a supernova’s white dwarf progenitor and its companion.

    Other coauthors on the paper are: S. R. Kulkarni of Caltech; D. Andrew Howell, Stefano Valenti of Las Cumbres Observatory Global Telescope Network and University of California Santa Barbara; Avishay Gal-Yam, Assaf Horesh, and Ilan Sagiv of the Weizmann Institute of Science; J. Johansson, R. Amanullah, A. Goobar, J. Sollerman, and F. Taddia of Stockholm University; S. Bradley Cenko and Neil Gehrels of the NASA Goddard Space Flight Center; Peter E. Nugent of Lawrence Berkeley National Laboratory; Iair Arcavi of Las Cumbres Observatory Global Telescope Network and the Kavli Institute for Theoretical Physics; Jason Surace of the Spitzer Science Center at Caltech; P. R.Woźniak and Daniela I. Moody of Los Alamos National Laboratory; Umaa D. Rebbapragada and Brian D. Bue of the Jet Propulsion Laboratory at Caltech.

    Supernova research at the OKC is supported by the Swedish Research Council and by the Knut and Alice Wallenberg Foundation. Some of the data presented here were obtained with the Nordic Optical Telescope, which is operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain. Some of the data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The observatory was made possible by the generous financial support of the W. M. Keck Foundation. This work also makes use of observations from the LCOGT network. Research at California Institute of Technology is supported by the National Science Foundation. LANL participation in iPTF is supported by the US Department of Energy as part of the Laboratory Directed Research and Development program. A portion of this work was carried out at the Jet Propulsion Laboratory under a Research and Technology Development Grant, under contract with the National Aeronautics and Space Administration.

    See the full article here.

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    Carnegie Institution of Washington Bldg

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

     
  • richardmitnick 7:24 am on April 18, 2015 Permalink | Reply
    Tags: , , , , Supernovas   

    From SOFIA: “NASA’s SOFIA Finds Missing Link Between Supernovae and Planet Formation” 

    NASA SOFIA Banner

    SOFIA (Stratospheric Observatory For Infrared Astronomy)

    March 19, 2015
    Last Updated: April 18, 2015
    Editor: Sarah Ramsey

    Felicia Chou
    Headquarters, Washington
    202-358-5241
    felicia.chou@nasa.gov

    Nicholas Veronico

    SOFIA Science Center, Moffett Field, Calif.
    650-604-4589 / 650-224-8726

    nicholas.a.veronico@nasa.gov / nveronico@sofia.usra.edu

    Kate K. Squires

    Armstrong Flight Research Center, Edwards, Calif. 

    661-276-2020 

    kate.k.squires@nasa.gov

    1

    Using NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA), an international scientific team discovered that supernovae are capable of producing a substantial amount of the material from which planets like Earth can form.

    These findings are published in the March 19 online issue of Science magazine.

    “Our observations reveal a particular cloud produced by a supernova explosion 10,000 years ago contains enough dust to make 7,000 Earths,” said Ryan Lau of Cornell University in Ithaca, New York.

    The research team, headed by Lau, used SOFIA’s airborne telescope and the Faint Object InfraRed Camera for the SOFIA Telescope, FORCAST, to take detailed infrared images of an interstellar dust cloud known as Supernova Remnant Sagittarius A East, or SNR Sgr A East.

    2
    Supernova remnant dust detected by SOFIA (yellow) survives away from the hottest X-ray gas (purple). The red ellipse outlines the supernova shock wave. The inset shows a magnified image of the dust (orange) and gas emission (cyan).Credits: NASA/CXO/Lau et al

    The team used SOFIA data to estimate the total mass of dust in the cloud from the intensity of its emission. The investigation required measurements at long infrared wavelengths in order to peer through intervening interstellar clouds and detect the radiation emitted by the supernova dust.

    Astronomers already had evidence that a supernova’s outward-moving shock wave can produce significant amounts of dust. Until now, a key question was whether the new soot- and sand-like dust particles would survive the subsequent inward “rebound” shock wave generated when the first, outward-moving shock wave collides with surrounding interstellar gas and dust.

    “The dust survived the later onslaught of shock waves from the supernova explosion, and is now flowing into the interstellar medium where it can become part of the ‘seed material’ for new stars and planets,” Lau explained.

    These results also reveal the possibility that the vast amount of dust observed in distant young galaxies may have been made by supernova explosions of early massive stars, as no other known mechanism could have produced nearly as much dust.

    “This discovery is a special feather in the cap for SOFIA, demonstrating how observations made within our own Milky Way galaxy can bear directly on our understanding of the evolution of galaxies billions of light years away,” said Pamela Marcum, a SOFIA project scientist at Ames Research Center in Moffett Field, California.

    For more information about SOFIA, visit:

    http://www.nasa.gov/sofia

    or

    http://www.dlr.de/en/sofia

    For information about SOFIA’s science mission and scientific instruments, visit:

    http://www.sofia.usra.edu

    or

    http://www.dsi.uni-stuttgart.de/index.en.html

    See the full article here.

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    SOFIA is a joint project of NASA and the German Aerospace Center (DLR). The aircraft is based at and the program is managed from NASA Armstrong Flight Research Center’s facility in Palmdale, California. NASA’s Ames Research Center, manages the SOFIA science and mission operations in cooperation with the Universities Space Research Association (USRA) headquartered in Columbia, Maryland, and the German SOFIA Institute (DSI) at the University of Stuttgart.
    NASA

     
  • richardmitnick 6:29 am on April 11, 2015 Permalink | Reply
    Tags: , , Supernovas,   

    From U Arizona: “Accelerating Universe? Not So Fast” 

    U Arizona bloc

    University of Arizona

    April 10, 2015
    Daniel Stolte

    1
    This Swift UVOT image shows galaxy M82 before the explosion and combines data acquired between 2007 and 2013. Mid-ultraviolet light is shown in blue, near-UV light in green and visible light in red. The image is 17 arcminutes across, or slightly more than half the apparent diameter of a full moon. (Credit: NASA/Swift/P. Brown, TAMU)

    A UA-led team of astronomers found that the type of supernovae commonly used to measure distances in the universe fall into distinct populations not recognized before. The findings have implications for our understanding of how fast the universe has been expanding since the Big Bang.

    2
    Swift’s UVOT captured the new supernova (circled) in three exposures taken on Jan. 22, 2014. Mid-ultraviolet light is shown in blue, near-UV light in green and visible light in red. Thick dust in M82 scatters much of the highest-energy light, which is why the supernova appears yellowish here. The image is 17 arcminutes across, or slightly more than half the apparent diameter of a full moon. (Credit: NASA/Swift/P. Brown, TAMU)

    Certain types of supernovae, or exploding stars, are more diverse than previously thought, a University of Arizona-led team of astronomers has discovered. The results, reported in two papers published in the Astrophysical Journal, have implications for big cosmological questions, such as how fast the universe has been expanding since the Big Bang.

    Most importantly, the findings hint at the possibility that the acceleration of the expansion of the universe might not be quite as fast as textbooks say.

    The team, led by UA astronomer Peter A. Milne, discovered that type Ia supernovae, which have been considered so uniform that cosmologists have used them as cosmic “beacons” to plumb the depths of the universe, actually fall into different populations. The findings are analogous to sampling a selection of 100-watt light bulbs at the hardware store and discovering that they vary in brightness.

    3
    An optical image of galaxy M101 obtained by Adam Block with the UA’s Mt. Lemmon Sky Center.

    U Arizona Mt Lemmon Sky Center
    Mt Lemmon

    4
    That same galaxy in a NASA Swift image, with bars indicating the location of supernova SN 2011fe. The Swift image is a false-color image with UV emission blue and optical emission red. (Image: NASA/Swift)

    “We found that the differences are not random, but lead to separating Ia supernovae into two groups, where the group that is in the minority near us are in the majority at large distances — and thus when the universe was younger,” said Milne, an associate astronomer with the UA’s Department of Astronomy and Steward Observatory. “There are different populations out there, and they have not been recognized. The big assumption has been that as you go from near to far, type Ia supernovae are the same. That doesn’t appear to be the case.”

    The discovery casts new light on the currently accepted view of the universe expanding at a faster and faster rate, pulled apart by a poorly understood force called dark energy. This view is based on observations that resulted in the 2011 Nobel Prize for Physics awarded to three scientists, including UA alumnus Brian P. Schmidt.

    The Nobel laureates discovered independently that many supernovae appeared fainter than predicted because they had moved farther away from Earth than they should have done if the universe expanded at the same rate. This indicated that the rate at which stars and galaxies move away from each other is increasing; in other words, something has been pushing the universe apart faster and faster.

    “The idea behind this reasoning,” Milne explained, “is that type Ia supernovae happen to be the same brightness — they all end up pretty similar when they explode. Once people knew why, they started using them as mileposts for the far side of the universe.

    “The faraway supernovae should be like the ones nearby because they look like them, but because they’re fainter than expected, it led people to conclude they’re farther away than expected, and this in turn has led to the conclusion that the universe is expanding faster than it did in the past.”

    Milne and his co-authors — Ryan J. Foley of the University of Illinois at Urbana-Champaign, Peter J. Brown at Texas A&M University and Gautham Narayan of the National Optical Astronomy Observatory, or NOAO, in Tucson — observed a large sample of type Ia supernovae in ultraviolet and visible light. For their study, they combined observations made by the Hubble Space Telescope with those made by NASA’s Swift satellite.

    NASA Hubble Telescope
    NASA/ESA Hubble

    NASA SWIFT Telescope
    NASA/Swift

    The data collected with Swift were crucial because the differences between the populations — slight shifts toward the red or the blue spectrum — are subtle in visible light, which had been used to detect type Ia supernovae previously, but became obvious only through Swift’s dedicated follow-up observations in the ultraviolet.

    “These are great results,” said Neil Gehrels, principal investigator of the Swift satellite, who co-authored the first paper. “I am delighted that Swift has provided such important observations, which have been made toward a science goal that is completely independent of the primary mission. It demonstrates the flexibility of our satellite to respond to new phenomena swiftly.”

    “The realization that there were two groups of type Ia supernovae started with Swift data,” Milne said. “Then we went through other datasets to see if we see the same. And we found the trend to be present in all the other datasets.

    “As you’re going back in time, we see a change in the supernovae population,” he added. “The explosion has something different about it, something that doesn’t jump out at you when you look at it in optical light, but we see it in the ultraviolet.

    “Since nobody realized that before, all these supernovae were thrown in the same barrel. But if you were to look at 10 of them nearby, those 10 are going to be redder on average than a sample of 10 faraway supernovae.”

    The authors conclude that some of the reported acceleration of the universe can be explained by color differences between the two groups of supernovae, leaving less acceleration than initially reported. This would, in turn, require less dark energy than currently assumed.

    “We’re proposing that our data suggest there might be less dark energy than textbook knowledge, but we can’t put a number on it,” Milne said. “Until our paper, the two populations of supernovae were treated as the same population. To get that final answer, you need to do all that work again, separately for the red and for the blue population.”

    The authors pointed out that more data have to be collected before scientists can understand the impact on current measures of dark energy. Scientists and instruments in Arizona will play important roles in these studies, according to Milne. These include projects led by NOAO; the Large Synoptic Survey Telescope, or LSST, whose primary mirror was produced at the UA; and a camera built by the UA’s Imaging Technology Lab for the Super-LOTIS telescope on Kitt Peak southwest of Tucson. Super-LOTIS is a robotic telescope that will use the new camera to follow up on gamma-ray bursts — the “muzzle flash” of a supernova — detected by Swift.

    LSST Exterior
    LSST Interior
    LSST

    NOAO Super-LOTIS Telescope
    Super-LOTIS

    Contacts

    Peter Milne
    Department of Astronomy/Steward Observatory
    520-626-5731
    pmilne@as.arizona.edu (link sends e-mail)

    See the full article here.

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    U Arizona campus

    The University of Arizona (UA) is a place without limits-where teaching, research, service and innovation merge to improve lives in Arizona and beyond. We aren’t afraid to ask big questions, and find even better answers.

    In 1885, establishing Arizona’s first university in the middle of the Sonoran Desert was a bold move. But our founders were fearless, and we have never lost that spirit. To this day, we’re revolutionizing the fields of space sciences, optics, biosciences, medicine, arts and humanities, business, technology transfer and many others. Since it was founded, the UA has grown to cover more than 380 acres in central Tucson, a rich breeding ground for discovery.

    Where else in the world can you find an astronomical observatory mirror lab under a football stadium? An entire ecosystem under a glass dome? Visit our campus, just once, and you’ll quickly understand why the UA is a university unlike any other.

     
  • richardmitnick 4:26 pm on March 19, 2015 Permalink | Reply
    Tags: , , , , Supernovas   

    From SOFIA: “NASA’s SOFIA Finds Missing Link Between Supernovae and Planet Formation” 

    NASA SOFIA Banner

    SOFIA (Stratospheric Observatory For Infrared Astronomy)

    March 19, 2015
    Felicia Chou
    Headquarters, Washington
    202-358-5241
    felicia.chou@nasa.gov

    Nicholas Veronico

    SOFIA Science Center, Moffett Field, Calif.
    650-604-4589 / 650-224-8726

    nicholas.a.veronico@nasa.gov / nveronico@sofia.usra.edu

    Kate K. Squires

    Armstrong Flight Research Center, Edwards, Calif. 

    661-276-2020 

    kate.k.squires@nasa.gov

    1
    SOFIA data reveal warm dust (white) surviving inside a supernova remnant. The SNR Sgr A East cloud is traced in X-rays (blue). Radio emission (red) shows expanding shock waves colliding with surrounding interstellar clouds (green). Image Credit: NASA/CXO/Herschel/VLA/Lau et al

    [These two following telescopes are clearly present in the above credit, important to the mission, but unnamed by the writers]

    ESA Herschel
    ESA/Herschel

    NRAO VLA
    NRAO/VLA

    Using NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA), an international scientific team discovered that supernovae are capable of producing a substantial amount of the material from which planets like Earth can form.

    These findings are published in the March 19 online issue of Science magazine.

    “Our observations reveal a particular cloud produced by a supernova explosion 10,000 years ago contains enough dust to make 7,000 Earths,” said Ryan Lau of Cornell University in Ithaca, New York.

    The research team, headed by Lau, used SOFIA’s airborne telescope and the Faint Object InfraRed Camera for the SOFIA Telescope, FORCAST, to take detailed infrared images of an interstellar dust cloud known as Supernova Remnant Sagittarius A East, or SNR Sgr A East.

    2
    Supernova remnant dust detected by SOFIA (yellow) survives away from the hottest X-ray gas (purple). The red ellipse outlines the supernova shock wave. The inset shows a magnified image of the dust (orange) and gas emission (cyan). Image Credit: NASA/CXO/Lau et al

    The team used SOFIA data to estimate the total mass of dust in the cloud from the intensity of its emission. The investigation required measurements at long infrared wavelengths in order to peer through intervening interstellar clouds and detect the radiation emitted by the supernova dust.

    Astronomers already had evidence that a supernova’s outward-moving shock wave can produce significant amounts of dust. Until now, a key question was whether the new soot- and sand-like dust particles would survive the subsequent inward “rebound” shock wave generated when the first, outward-moving shock wave collides with surrounding interstellar gas and dust.

    “The dust survived the later onslaught of shock waves from the supernova explosion, and is now flowing into the interstellar medium where it can become part of the ‘seed material’ for new stars and planets,” Lau explained.

    These results also reveal the possibility that the vast amount of dust observed in distant young galaxies may have been made by supernova explosions of early massive stars, as no other known mechanism could have produced nearly as much dust.

    “This discovery is a special feather in the cap for SOFIA, demonstrating how observations made within our own Milky Way galaxy can bear directly on our understanding of the evolution of galaxies billions of light years away,” said Pamela Marcum, a SOFIA project scientist at Ames Research Center in Moffett Field, California.

    SOFIA is a heavily modified Boeing 747 Special Performance jetliner that carries a telescope with an effective diameter of 100 inches (2.5 meters) at altitudes of 39,000 to 45,000 feet (12 to 14 km). SOFIA is a joint project of NASA and the German Aerospace Center. The aircraft observatory is based at NASA’s Armstrong Flight Research Center facility in Palmdale, California. The agency’s Ames Research Center in Moffett Field, California, is home to the SOFIA Science Center, which is managed by NASA in cooperation with the Universities Space Research Association in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart.

    For more information about SOFIA, visit:

    http://www.nasa.gov/sofia

    or

    http://www.dlr.de/en/sofia

    For information about SOFIA’s science mission and scientific instruments, visit:

    http://www.sofia.usra.edu

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    SOFIA is a joint project of NASA and the German Aerospace Center (DLR). The aircraft is based at and the program is managed from NASA Armstrong Flight Research Center’s facility in Palmdale, California. NASA’s Ames Research Center, manages the SOFIA science and mission operations in cooperation with the Universities Space Research Association (USRA) headquartered in Columbia, Maryland, and the German SOFIA Institute (DSI) at the University of Stuttgart.
    NASA

     
  • richardmitnick 10:26 am on March 19, 2015 Permalink | Reply
    Tags: , , , Supernovas   

    From Nautilus: “The Secret History of the Supernova at the Bottom of the Sea” 

    Nautilus

    Nautilus

    March 19, 2015
    Julia Rosen

    How a star explosion may have shaped life on Earth.

    In February 1987, Neil Gehrels, a young researcher at NASA’s Goddard Space Flight Center, boarded a military plane bound for the Australian Outback. Gehrels carried some peculiar cargo: a polyethylene space balloon and a set of radiation detectors he had just finished building back in the lab. He was in a hurry to get to Alice Springs, a remote outpost in the Northern Territory, where he would launch these instruments high above Earth’s atmosphere to get a peek at the most exciting event in our neck of the cosmos: a supernova exploding in one of the Milky Way’s nearby satellite galaxies.

    Like many supernovas, SN 1987A announced the violent collapse of a massive star.

    1
    http://www.eso.org/public/images/eso1401a/
    Remnant of SN 1987A seen in light overlays of different spectra. ALMA data (radio, in red) shows newly formed dust in the center of the remnant. Hubble (visible, in green) and Chandra (X-ray, in blue) data show the expanding shock wave.

    ALMA Array
    ALMA

    NASA Hubble Telescope
    Hubble

    NASA Chandra Telescope

    Chandra

    What set it apart was its proximity to Earth; it was the closest stellar cataclysm since Johannes Kepler spotted one in our own Milky Way galaxy in 1604. Since then, scientists have thought up many questions that to answer would require a front row seat to another supernova. They were questions like this: How close does a supernova need to be to devastate life on Earth?

    Back in the 1970s, researchers hypothesized that radiation from a nearby supernova could annihilate the ozone layer, exposing plants and animals to harmful ultraviolet light, and possibly cause a mass extinction. Armed with new data from SN 1987A, Gehrels could now calculate a theoretical radius of doom, inside which a supernova would have grievous effects, and how often dying stars might stray inside it.

    “The bottom line was that there would be a supernova close enough to the Earth to drastically affect the ozone layer about once every billion years,” says Gehrels, who still works at Goddard. That’s not very often, he admits, and no threatening stars prowl the solar system today. But Earth has existed for 4.6 billion years, and life for about half that time, meaning the odds are good that a supernova blasted the planet sometime in the past. The problem is figuring out when. Because supernovas mainly affect the atmosphere, it’s hard to find the smoking gun,”Gehrels says.

    Astronomers have searched the surrounding cosmos for clues, but the most compelling evidence for a nearby supernova comes—somewhat paradoxically—from the bottom of the sea. Here, a dull and asphalt black mineral formation called a ferromanganese crust grows on the bare bedrock of underwater mountains—incomprehensibly slowly. In its thin, laminated layers, it records the history of planet Earth and, according to some, the first direct evidence of a nearby supernova.

    1
    Plain-looking, but important: Ferromanganese crusts collected by Hein nearby Hawaii.James Hein

    These kinds of clues about ancient cosmic explosions are immensely valuable to scientists, who suspect that supernovas may have played a little-known role in shaping the evolution of life on Earth. “This actually could have been part of the story of how life has gone on, and the slings and arrows that it had to dodge,” says Brian Fields, an astronomer at the University of Illinois at Urbana-Champaign. But to understand just how supernovas affected life, scientists needed to link the timing of their explosions to pivotal events on earth such as mass extinctions or evolutional leaps. The only way to do that is to trace the debris they deposited on Earth by finding elements on our planet that are primarily fused inside supernovas.

    Fields and his colleagues named a few of such supernova-forged elements—mainly rare radioactive metals that decay slowly, making their presence a sure sign of an expired star. One of the most promising candidates was Fe-60, a heavy isotope of iron with four more neutrons than the regular isotope and a half-life of 2.6 million years. But finding Fe-60 atoms scattered on the Earth’s surface was no easy task. Fields estimated that only a very small amount of Fe-60 would have actually reached our planet, and on land, it would have been diluted by natural iron, or been eroded and washed away over millions of years.

    So scientists looked instead at bottom of the sea, where they found Fe-60 atoms in the ferromanganese crusts, which are rocks that form a bit like stalagmites: They precipitate out of liquid, adding successive layers, except they are composed of metals and form extensive blankets instead of individual spires. Composed primarily of iron and manganese oxides, they also contain small amounts of almost every metal in the periodic table, from cobalt to yttrium.

    As iron, manganese, and other metal ions wash into the sea from land or gush from underwater volcanic vents, they react with the oxygen in seawater, forming solid substances that precipitate onto the ocean floor or float around until they adhere to existing crusts. James Hein at the United States Geological Survey, who studied crusts for more than 30 years, says that it remains a mystery exactly how they establish themselves on rocky stretches of seafloor, but once the first layer accumulates, more layers pile on—up to 25 cm thick.

    That enables crusts to serve as cosmic historians that keep records of seawater chemistry, including the elements that serve as timestamps of dying stars. One of the oldest crusts, fished out by Hein southwest of Hawaii in the 1980s, dates back more than 70 million years, to a time when dinosaurs roamed the planet and the Indian subcontinent was just an island in the ocean halfway between Antarctica and Asia.

    The crusts’ growth is one the slowest processes known to science—they put on about five millimeters every million years. For comparison, human fingernails grow about seven million times faster. The reason for that is plain math. There’s less than one atom of iron or manganese for every billion molecules of water in the ocean—and then they must resist the pull of passing currents and the power of other chemical interactions that might pry them loose until they get trapped by the next layer.

    Unlike the slow-growing crusts, however, supernova explosions happen almost instantly. The most common type of supernova occurs when a star runs out of its hydrogen and helium fuel, causing its core to burn heavier elements until it eventually produces iron. That process can take millions of years, but the star’s final moments take only milliseconds. As heavy elements accumulate in the core, it becomes unstable and implodes, sucking the outer layers inward at a quarter of the speed of light. But the density of particles in the core soon repels the implosion, triggering a massive explosion that shoots a cloud of stellar debris out into space—including Fe-60 isotopes, some of which eventually find their home in ferromanganese crusts.

    2
    Meet the Earth’s historian: Klaus Knie used this 25 cm-thick ferromanganese crust sampled from the depth of 4,830m in the Pacific Ocean to trace the Fe-60 isotopes. Anton Wallner

    The first people to look for the Fe-60 in these crusts were Klaus Knie, an experimental physicist then at the Technical University of Munich, and his collaborators. Knie’s team was studying neither supernovas nor crusts—they were developing methods for measuring rare isotopes of various elements—including Fe-60. After another scientist measured an isotope of beryllium, which can be used to date the layers of the crusts, Knie decided to examine the same specimen for Fe-60, which he knew was produced in supernovas. “We are part of the universe and we have the chance to hold the ‘astrophysical’ matter in our hand, if we look at the right places,” says Knie, who is now at the GSI Helmholtz Center for Heavy Ion Research.

    The crust, also plucked from the seafloor not far from Hawaii, turned out to be the right place: Knie and his colleagues found a spike in Fe-60 in layers that dated back about 2.8 million years, which they say signaled the death of a nearby star around that time. Knie’s discovery was important in several ways. It represented the first evidence that supernova debris can be found here on Earth and it pinpointed the approximate timing of the last nearby supernova blast (if there had been a more recent one, Knie would have found more recent Fe-60 spikes.). But it also enabled Knie to propose an interesting evolutionary theory.

    Based on the concentration of Fe-60 in the crust, Knie estimated that the supernova exploded at least 100 light-years from Earth—three times the distance at which it could’ve obliterated the ozone layer—but close enough to potentially alter cloud formation, and thus, climate. While no mass-extinction events happened 2.8 million years ago, some drastic climate changes did take place—and they may have given a boost to human evolution. Around that time, the African climate dried up, causing the forests to shrink and give way to grassy savanna. Scientists think this change may have encouraged our hominid ancestors as they descended from trees and eventually began walking on two legs.

    That idea, as any young theory, is still speculative and has its opponents. Some scientists think Fe-60 may have been brought to Earth by meteorites, and others think these climate changes can be explained by decreasing greenhouse gas concentrations, or the closing of the ocean gateway between North and South America. But Knee’s new tool gives scientists the ability to date other, possibly more ancient, supernovas that may have passed in the vicinity of Earth, and to study their influence on our planet. It is remarkable that we can use these dull, slow-growing rocks to study the luminous, rapid phenomena of stellar explosions, Fields says. And they’ve got more stories to tell.

    3
    Lead composite image credit: Pinwheel-Shaped Galaxy by NASA, ESA, The Hubble Heritage Team, (STScI/AURA) and A. Riess (STScI) and Red Sea Coral Reef by Wusel700

    See the full article here.

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  • richardmitnick 8:41 am on March 17, 2015 Permalink | Reply
    Tags: , , , Supernovas   

    From CAASTRO: “Clues to origin of luminous supernovae may lie in ultraviolet” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    17 March 2015

    1

    The widespread use of type Ia supernovae (SNe Ia) in cosmology, as one of the farthest rungs in the extragalactic distance ladder and as tools to study dark energy, depends on the accuracy with which their luminosity can be measured. The classic luminosity calibration relations used in cosmological studies apply only to SNe Ia with “normal” spectra. However, wide-field supernova searches (including CAASTRO’s SkyMapper survey) are now revealing the true observational diversity of SNe Ia, uncovering a rare, ultraluminous subclass of SNe Ia which do not obey the calibration relations.

    2

    ANU-based CAASTRO Associate Investigator Dr Richard Scalzo’s previous work on this subclass provides strong evidence that their ejected masses exceed the Chandrasekhar limiting mass for white dwarfs, justifying the commonly used label “super-Chandra”. Since all type Ia supernovae are believed to be explosions of white dwarfs, SNe Ia provide challenges to our understanding of white dwarf physics and stellar evolution. Super-Chandra SNe Ia are not only very luminous, but very blue – suggesting strong ultraviolet (UV) emission, which could arise from a shock driven by the supernova ejecta into a cloud of material surrounding the progenitor. Such clouds are also predicted by models of white dwarf mergers, and could explain the high luminosities of super-Chandra SNe Ia.

    With a spectrum resembling other super-Chandra SNe Ia, LSQ12gdj was discovered just a few days after explosion – making it an excellent test case to search for UV emission from shocks. Dr Scalzo, the ANU group, and their European and American collaborators observed LSQ12gdj with the Swift space telescope as well as ground-based optical telescopes.

    NASA SWIFT Telescope
    NASA/Swift

    Early in its evolution, over a quarter of LSQ12gdj’s luminosity was emitted at UV wavelengths visible only to Swift (compared with 5-10% for normal SNe Ia). However, no more than 10% of LSQ12gdj’s peak luminosity is likely to come from shocks, so any material surrounding the progenitor must be very compact. When all this is taken into account, LSQ12gdj’s appearance is consistent with a Chandrasekhar-mass progenitor – showing that UV observations are crucial to understand these events fully.

    Publication details:

    R. A. Scalzo, M. Childress, B. Tucker, F. Yuan, B. Schmidt, P. J. Brown, C. Contreras, N. Morrell, E. Hsiao, C. Burns, M. M. Phillips, A. Campillay, C. Gonzalez, K. Krisciunas, M. Stritzinger, M. L. Graham, J. Parrent, S. Valenti, C. Lidman, B. Schaefer, N. Scott, M. Fraser, A. Gal-Yam, C. Inserra, K. Maguire, S. J. Smartt, J. Sollerman, M. Sullivan, F. Taddia, O. Yaron, D. R. Young, S. Taubenberger, C. Baltay, N. Ellman, U. Feindt, E. Hadjiyska, R. McKinnon, P. E. Nugent, D. Rabinowitz, E. S. Walker in MNRAS 445 (2014) Early ultraviolet emission in the Type Ia supernova LSQ12gdj: No evidence for ongoing shock interaction

    See the full article here.

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    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

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  • richardmitnick 4:47 pm on January 21, 2015 Permalink | Reply
    Tags: Australia National University, , , Supernovas   

    From phys.org: “Ocean floor dust gives new insight into supernovae” 

    physdotorg
    phys.org

    Jan 20, 2015
    No Writer Credit

    1
    Dr Anton Wallner in the Nuclear Physics Department at Australian National University. Credit: Stuart Hay, ANU

    Scientists plumbing the depths of the ocean have made a surprise finding that could change the way we understand Scientists plumbing the depths of the ocean have made a surprise finding that could change the way we understand supernovae, exploding stars way beyond our solar system.

    They have analysed extraterrestrial dust thought to be from supernovae, that has settled on ocean floors to determine the amount of heavy elements created by the massive explosions.

    “Small amounts of debris from these distant explosions fall on the earth as it travels through the galaxy,” said lead researcher Dr Anton Wallner, from the Research School of Physics and Engineering.

    “We’ve analysed galactic dust from the last 25 million years that has settled on the ocean and found there is much less of the heavy elements such as plutonium and uranium than we expected.”

    The findings are at odds with current theories of supernovae, in which some of the materials essential for human life, such as iron, potassium and iodine are created and distributed throughout space.

    Supernovae also create lead, silver and gold, and heavier radioactive elements such as uranium and plutonium.

    Dr Wallner’s team studied plutonium-244 which serves as a radioactive clock by the nature of its radioactive decay, with a half-life of 81 million years.

    “Any plutonium-244 that existed when the earth formed from intergalactic gas and dust over four billion years ago has long since decayed,” Dr Wallner said.

    “So any plutonium-244 that we find on earth must have been created in explosive events that have occurred more recently, in the last few hundred million years.”

    The team analysed a 10 centimetre-thick sample of the earth’s crust, representing 25 million years of accretion, as well as deep-sea sediments collected from a very stable area at the bottom of the Pacific Ocean.

    “We found 100 times less plutonium-244 than we expected,” Dr Wallner said.

    “It seems that these heaviest elements may not be formed in standard supernovae after all. It may require rarer and more explosive events such as the merging of two neutron stars to make them.”

    The fact that these heavy elements like plutonium were present, and uranium and thorium are still present on earth suggests that such an explosive event must have happened close to the earth around the time it formed, said Dr Wallner.

    “Radioactive elements in our planet such as uranium and thorium provide much of the heat that drives continental movement, perhaps other planets don’t have the same heat engine inside them,” he said.

    The research is published in Nature Communications., exploding stars way beyond our solar system.

    They have analysed extraterrestrial dust thought to be from supernovae, that has settled on ocean floors to determine the amount of heavy elements created by the massive explosions.

    “Small amounts of debris from these distant explosions fall on the earth as it travels through the galaxy,” said lead researcher Dr Anton Wallner, from the Research School of Physics and Engineering.

    “We’ve analysed galactic dust from the last 25 million years that has settled on the ocean and found there is much less of the heavy elements such as plutonium and uranium than we expected.”

    The findings are at odds with current theories of supernovae, in which some of the materials essential for human life, such as iron, potassium and iodine are created and distributed throughout space.

    Supernovae also create lead, silver and gold, and heavier radioactive elements such as uranium and plutonium.

    Dr Wallner’s team studied plutonium-244 which serves as a radioactive clock by the nature of its radioactive decay, with a half-life of 81 million years.

    “Any plutonium-244 that existed when the earth formed from intergalactic gas and dust over four billion years ago has long since decayed,” Dr Wallner said.

    “So any plutonium-244 that we find on earth must have been created in explosive events that have occurred more recently, in the last few hundred million years.”

    The team analysed a 10 centimetre-thick sample of the earth’s crust, representing 25 million years of accretion, as well as deep-sea sediments collected from a very stable area at the bottom of the Pacific Ocean.

    “We found 100 times less plutonium-244 than we expected,” Dr Wallner said.

    “It seems that these heaviest elements may not be formed in standard supernovae after all. It may require rarer and more explosive events such as the merging of two neutron stars to make them.”

    The fact that these heavy elements like plutonium were present, and uranium and thorium are still present on earth suggests that such an explosive event must have happened close to the earth around the time it formed, said Dr Wallner.

    “Radioactive elements in our planet such as uranium and thorium provide much of the heat that drives continental movement, perhaps other planets don’t have the same heat engine inside them,” he said.

    The research is published in Nature Communications.

    See the full article here.

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    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 4:24 pm on October 17, 2014 Permalink | Reply
    Tags: , , , , , Supernovas   

    From Daily Galaxy: “Long-Sought Source of Massive Supernovas Detected” 

    Daily Galaxy
    The Daily Galaxy

    October 17, 2014
    No Writer Credit

    For years astronomers have searched for the elusive progenitors of hydrogen-deficient stellar explosions without success. However, this changed in June 2013 with the appearance of supernova iPTF13bvn and the subsequent detection of an object at the same location in archival images obtained before the explosion using the HST. The interpretation of the observed object is controversial. The team led by [Melina] Bersten presented a self-consistent picture using models of supernova brightness and progenitor evolution. In their picture, the more massive star in a binary system explodes after transferring mass to its companion.

    A group of researchers recently presented a model that provides the first characterization of the progenitor for a hydrogen-deficient supernova. Their model predicts that a bright hot star, which is the binary companion to an exploding object, remains after the explosion. To verify their theory, the group secured observation time with the Hubble Space Telescope (HST) to search for such a remaining star. Their findings, which are reported in the October 2014 issue of The Astronomical Journal, have important implications for the evolution of massive stars.

    NASA Hubble Telescope
    NASA Hubble schematic
    NASA/ESA Hubble

    One of the challenges in astrophysics is identifying which star produces which supernova. This is particularly problematic for supernovae without hydrogen, which are called Types Ib or Ic, because the progenitors have yet to be detected directly.

    The ultimate question is: “How do progenitor stars remove their hydrogen-rich envelopes during their evolution?” Two competing mechanisms have been proposed. One hypothesizes that a strong wind produced by a very massive star blows the outer hydrogen layers, while the other suggests that a gravitationally bound binary companion star removes the outer layers. The latter case does not require a very massive star. Because these two scenarios predict vastly different progenitor stars, direct detection of the progenitor for this type of supernova can provide definitive clues about the preferred evolutionary path.

    When young Type Ib supernova iPTF13bvn was discovered in nearby Spiral_galaxy NGC 5806, astronomers hoped to find its progenitor. Inspecting the available HST images did indeed reveal an object, providing optimism that the first hydrogen-free supernova progenitor would at last be identified. Due to the object’s blue hue, it was initially suggested that the object was a very hot, very massive, evolved star with a compact structure, called a “Wolf-Rayet” star. (Using models of such stars, a group based in Geneva was able to reproduce the brightness and color of the pre-explosion object with a Wolf-Rayet star that was born with over 30 times the mass of the Sun and died with 11 times the solar mass.)

    ngc5806
    NGC 5806

    burt
    Image shows spiral galaxy NGC5806 Left top: Zoomed image of supernova iPTF13bvn just after the explosion. Left bottom: HST image taken before the explosion. Progenitor of iPTF13bvn was identified. Right: Spiral galaxy NGC5806 Left top: Zoomed image of supernova iPTF13bvn just after the explosion. Left bottom: HST image taken before the explosion. Progenitor of iPTF13bvn was identified. (Image Credit: Iair Arcavi, Weizmann Institute of Science, PTF)

    “Based on such suggestions, we decided to check if such a massive star is consistent with the supernova brightness evolution,” says Melina Bersten of Kavli IPMU who led the research. However, the results are inconsistent with a Wolf-Rayet star; the exploding star must have been merely four times the mass of the Sun, which is much smaller than a Wolf-Rayet star. “If the mass was this low and the supernova lacked hydrogen, our immediate conclusion is that the progenitor was part of a binary system,” adds Bersten.

    Because the problem requires a more elaborate solution, the team set out to simulate the evolution of a binary system with mass transfer in order to determine a configuration that can explain all the observational evidence (a blue pre-explosion object with a relatively low mass devoid of hydrogen). “We tested several configurations and came up with a family of possible solutions,” explains Omar Benvenuto of IALP, Argentina. “Interestingly, the mass transfer process dictates the observational properties of the exploding star, so it allows suitable solutions to be derived even if the mass of the stars is varied,” adds Benvenuto. The team chose the case where two stars are born with 20 and 19 times the mass of the Sun. The mass transfer process causes the larger star to retain only four times the solar mass before exploding. Most importantly, the smaller star may trap part of the transferred mass, becoming a very bright and hot star.

    The existence of a hot star would provide strong evidence for the binary model presented by Bersten and collaborators. Fortunately, such a prediction can be directly tested once the supernova fades because the hot companion should become evident. “We have requested and obtained observation time with the HST to search for the companion star in 2015,” comments Gaston Folatelli of Kavli IPMU. “Until then, we must wait patiently to see if we can identify the progenitor of a hydrogen-free supernova for the first time,” Bersten adds.

    See the full article here.

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  • richardmitnick 8:35 am on August 8, 2014 Permalink | Reply
    Tags: , , , , , Supernovas   

    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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