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  • 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.

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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 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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    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    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
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    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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    About Phys.org in 100 Words

    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
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    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
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    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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  • richardmitnick 4:45 pm on July 31, 2014 Permalink | Reply
    Tags: , , , , , Supernovas   

    From SPACE.com: “Weird Supernova May Blow Away Star Explosion Theories” 

    space-dot-com logo

    SPACE.com

    July 31, 2014
    Jesse Emspak

    Light from a radioactive metal forged inside a supernova blast could prompt a rethink of how some star explosions occur.

    image
    This image from NASA’s Swift space telescope, taken on Jan. 22, 2014, shows the supernova SN 2014J as seen in three different exposures by the space observatory. Scientists suspect the weird supernova’s progenitor star may have had a helium belt. Credit: NASA/Swift/P. Brown, TAMU

    The supernova SN 2014J is located 11.4 million light-years from Earth in the galaxy M82. Astronomers used the European Space Agency’s International Gamma-Ray Astrophysics Laboratory (INTEGRAL) spacecraft to examine the star explosion’s light spectrum in the gamma-ray bands and saw elements that shouldn’t have been there — suggesting that widely accepted models of how such events happen might be incomplete.

    ESA Integral
    ESA/INTEGRAL

    m82.
    To celebrate the Hubble Space Telescope’s 16 years of success, the two space agencies involved in the project, NASA and the European Space Agency (ESA), are releasing this image of the magnificent starburst galaxy, Messier 82 (M82). This mosaic image is the sharpest wide-angle view ever obtained of M82. The galaxy is remarkable for its bright blue disk, webs of shredded clouds, and fiery-looking plumes of glowing hydrogen blasting out of its central regions.

    Throughout the galaxy’s center, young stars are being born 10 times faster than they are inside our entire Milky Way Galaxy. The resulting huge concentration of young stars carved into the gas and dust at the galaxy’s center. The fierce galactic superwind generated from these stars compresses enough gas to make millions of more stars.

    In M82, young stars are crammed into tiny but massive star clusters. These, in turn, congregate by the dozens to make the bright patches, or “starburst clumps,” in the central parts of M82. The clusters in the clumps can only be distinguished in the sharp Hubble images. Most of the pale, white objects sprinkled around the body of M82 that look like fuzzy stars are actually individual star clusters about 20 light-years across and contain up to a million stars.

    The rapid rate of star formation in this galaxy eventually will be self-limiting. When star formation becomes too vigorous, it will consume or destroy the material needed to make more stars. The starburst then will subside, probably in a few tens of millions of years.

    Located 12 million light-years away, M82 appears high in the northern spring sky in the direction of the constellation Ursa Major, the Great Bear. It is also called the “Cigar Galaxy” because of the elliptical shape produced by the oblique tilt of its starry disk relative to our line of sight.

    The observation was made in March 2006, with the Advanced Camera for Surveys’ Wide Field Channel. Astronomers assembled this six-image composite mosaic by combining exposures taken with four colored filters that capture starlight from visible and infrared wavelengths as well as the light from the glowing hydrogen filaments.

    Scientists with the Max Planck Institute for Extraterrestrial Physics in Germany made the supernova discovery.

    A strange supernova

    SN 2014J is a type Ia supernova. Type Ia supernovas occur in binary systems with two stars in orbits so close that the stars exchange mass. As the more massive star of the pair ages it evolves into a white dwarf, a star that is the size of Earth but has up to 1.4 times the mass of the sun. The companion star’s outer envelope gets pulled to the tiny, but very dense, dwarf’s surface.

    Over time, the gas piles up on the white dwarf until enough pressure and heat build up and ignite fusion reactions. The hydrogen becomes helium, and then the helium goes through the “triple alpha” process, fusing into carbon and oxygen. Since the fusion is happening very quickly and the gravity of the white dwarf is so large, there’s not enough time for the gas to expand and the stuff on the white dwarf surface explodes. The explosion is so powerful that it disrupts the white dwarf’s interior, obliterating it and seeding the rest of the universe with heavy elements.

    What the Max Planck team saw was a gamma-ray signature of nickel-56, a radioactive isotope of the metal that emits gamma rays as it decays into cobalt-56. It has a half-life of only about six days, but the gamma rays were still visible 15 days after the supernova blew up.

    “We were observing it and after about three weeks most of nickel-56 would have decayed,” said Roland Diehl, lead author of the study. “The nickel-56 would be cobalt. But we saw the gamma-ray line… Some of our colleagues said that can’t be true.”

    A helium belt?

    The spectral line was also narrow and sharp, when it should have been wider and more diffuse – the result of moving toward the observers along the line of sight in the wake of the explosion. The blast should have also been relatively symmetrical. But it wasn’t.

    That led Diehl and his colleagues to think there had to be a “belt” of helium around the white dwarf’s equator, which would account for the supernova’s shape. Seeing the nickel could be explained if the view was pole-on, so that the helium fusing into other elements such as carbon and oxygen wouldn’t block the light from the nickel.

    The hypotheses in Diehl’s study also depend on the accretion of mass being relatively fast. Too slow and the white dwarf turns into either a more massive dwarf or a neutron star. On top of that, any gas that reaches the surface of a white dwarf tends to “flatten out” and cover the surface evenly because the gravity is so strong.

    The next question is where the helium came from. There are two possible sources. One is a companion star, but most stars don’t have a lot of helium in their outer envelopes unless they are rather massive to begin with.

    “Usually stars with bigger [helium] cores evolve faster, so the star with the bigger core should die first,” said Alexander Heger, a professor of physics at Monash University in Australia, in an email to Space.com. “The only way out would be to have a system with more than one phase of mass transfer, i.e., the star that is now the less massive white dwarf initially was the more massive star but by the time it died it had transferred a lot of mass to the companion. Such models and details of mass transfer and ejection from the system are still quite uncertain.”

    Alternate theories

    The other possibility is a helium white dwarf, orbiting close enough to a companion white dwarf that it nearly grazes it.

    Helium white dwarfs are hard to create because a star that could become one on its own would have a low mass, on the order of 0.6 times the mass of Earth’s sun, said Enrico Ramirez-Ruiz, a professor of astronomy at the University of California, Santa Cruz. Such stars would take so long to become white dwarfs that the universe hasn’t been around long enough for them to form.

    Ramirez-Ruiz, who was not involved in Diehl’s research, said that’s why the traditional model of type Ia supernovas needs tweaking. To get the helium there is probably some kind of mass exchange between the two stars in a binary system as well as between the remaining aged star and white dwarf, and even between two white dwarf stars.

    Diehl’s observations, he said, are the first time anyone has seen clear evidence of that kind of supernova, as well as the nickel.

    The nickel is important, because it shows the disruption at the center of the white dwarf, evidence for a “double detonation” model. In that scenario, the explosive fusion of the helium on the white dwarf surface produces a kind of focused shockwave that triggers yet other fusion reactions inside the dwarf, leading to the production of radioactive nickel.

    “It’s really forced us to revisit the old models,” Ramirez-Ruiz said.

    Their research is detailed in the Aug. 1 issue of the journal Science.

    See the full article here.


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  • richardmitnick 12:36 pm on July 21, 2014 Permalink | Reply
    Tags: , , , , , , Supernovas   

    From Oak Ridge Lab: “‘Engine of Explosion’ Discovered at OLCF now Observed in Nearby Supernova Remnant’ 

    i1

    Oak Ridge National Laboratory

    May 6, 2014
    Katie Elyce Jones

    Data gathered with high-energy x-ray telescope support the SASI model—a decade later

    Back in 2003, researchers using the Oak Ridge Leadership Computing Facility’s (OLCF’s) first supercomputer, Phoenix, started out with a bang. Astrophysicists studying core-collapse [Type II]supernovae—dying massive stars that violently explode after running out of fuel—asked themselves what mechanism triggers explosion and a fusion chain reaction that releases all the elements found in the universe, including those that make up the matter around us?

    “This is really one of the most important problems in science because supernovae give us all the elements in nature,” said Tony Mezzacappa of the University of Tennessee–Knoxville.

    Leading up to the 2003 simulations on Phoenix, one-dimensional supernovae models simulated a shock wave that pushes stellar material outward, expanding to a certain radius before, ultimately, succumbing to gravity. The simulations did not predict that stellar material would push beyond the shock wave radius; instead, infalling matter from the fringes of the expanding star tamped the anticipated explosion. Yet, humans have recorded supernovae explosions throughout history.

    “There have been a lot of supernovae observations,” Mezzacappa said. “But these observations can’t really provide information on the engine of explosion because you need to observe what is emitted from deep within the supernova, such as gravitational waves or neutrinos. It’s hard to do this from Earth.”

    Then simulations on Phoenix offered a solution: the SASI, or standing accretion shock instability, a sloshing of stellar material that destabilizes the expanding shock and helps lead to an explosion.

    “Once we discovered the SASI, it became very much a part of core-collapse supernova theory,” Mezzacappa said. “People feel it is an important missing ingredient.”

    The SASI provided a logical answer supported by other validated physics models, but it was still theoretical because it had only been demonstrated computationally.

    Now, more than a decade later, researchers mapping radiation signatures from the Cassiopeia A supernova with NASA’s NuSTAR high-energy x-ray telescope array have published observational evidence that supports the SASI model.

    NASA NuSTAR
    NASA/NuStar

    Cass A
    Cas A
    A false color image off Cassiopeia using observations from both the Hubble and Spitzer telescopes as well as the Chandra X-ray Observatory (cropped).
    Courtesy NASA/JPL-Caltech

    “What they’re seeing are x-rays that come from the radioactive decay of Titanium-44 in Cas A,” Mezzacappa said.

    Because Cassiopeia A is only 11,000 light-years away within the Milky Way galaxy (relatively nearby in astronomical distances), NuSTAR is capable of detecting Ti-44 located deep in the supernova ejecta. Mapping the radiative signature of this titanium isotope provides information on the supernova’s engine of explosion.

    “The distribution of titanium is what suggests that the supernova ‘sloshes’ before it explodes, like the SASI predicts,” Mezzacappa said.

    This is a rare example of simulation predicting a physical phenomenon before it is observed experimentally.

    “Usually it’s the other way around. You observe something experimentally then try to model it,” said the OLCF’s Bronson Messer. “The SASI was discovered computationally and has now been confirmed observationally.”

    The authors of the Nature letter that discusses the NuSTAR results cite Mezzacappa’s 2003 paper introducing the SASI in The Astrophysical Journal, which was coauthored by John Blondin and Christine DeMarino, as a likely model to describe the Ti-44 distribution.

    Despite observational support for the SASI, researchers are uncertain whether the SASI is entirely responsible for triggering a supernova explosion or if it is just part of the explanation. To further explore the model, Mezzacappa’s team, including the Innovative and Novel Computational Impact on Theory and Experiment (INCITE) project’s principal investigator Eric Lentz, are taking supernovae simulations to the next level on the OLCF’s 27-petaflop Titan supercomputer located at Oak Ridge National Laboratory.

    ORNL Titan Supercomputer
    Titan at ORNL

    “The role of the SASI in generating explosion and whether or not the models are sufficiently complete to predict the course of explosion is the important question now,” Mezzacappa said. “The NuSTAR observation suggests it does aid in generating the explosion.”

    Although the terascale runs that predicted the SASI in 2003 were in three dimensions, they did not include much of the physics that can now be solved on Titan. Today, the team is using 85 million core hours and scaling to more than 60,000 cores to simulate a supernova in three dimensions with a fully physics-based model. The petascale Titan simulation, which will be completed later this year, could be the most revealing supernova explosion yet—inside our solar system anyway.

    ORNL is managed by UT-Battelle for the Department of Energy’s Office of Science. DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

    See the full article here.

    i2


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  • richardmitnick 2:29 pm on July 1, 2014 Permalink | Reply
    Tags: , , , , Supernovas,   

    From Symmetry: “Waiting for supernova” 

    Symmetry

    July 01, 2014
    Fermilab Leah Hesla
    Leah Hesla

    Catching a nearby supernova would be a once-in-a-lifetime experience that could give scientists a glimpse into physics they could never recreate on Earth.

    Thousands of years ago, when a stargazer noticed a bright, new speck in the sky, one that wasn’t there the night before, he likely would have been mystified. For early astronomers, stars were eternal, appearing faithfully on the dark firmament night after night since the beginning of time. What message might the gods be sending by throwing this newcomer into the familiar pattern?

    “If stars developed on a faster time scale, then people might have been able to figure out sooner, ‘Gee, they’re not just points painted on the ceiling,’” says John Beacom, a physicist at The Ohio State University. “They didn’t know how to decode it when a new star appeared, and they couldn’t guess it was a star exploding.”

    Nowadays physicists not only are aware of these celestial explosions, they eagerly await the next one to happen nearby. An exploding star’s intense conditions could provide us with a glimpse of physics that we could never recreate on Earth.

    Supernovae are not rare. Every second, a few stars in the universe expire as supernovae. But it’s a big universe, and in our own Milky Way, only two or three go off every hundred years, scientists estimate. The last observed supernova went off in the Large Magellanic Cloud, just outside the Milky Way at a distance of 163,000 light-years from Earth. That was seen in 1987. The last observed supernova in our own galaxy was Kepler’s Star, spotted in 1604. It was 20,000 light-years away.

    Supernovae come in two types. One type of supernova [Type 1A] is born when two white dwarfs merge or when, in a binary star system consisting of a white dwarf and another type of star, the white dwarf accretes too much material from the other. The overwhelming mass of the merged star compresses it to the point that the resulting heat ignites a thermonuclear runaway.

    A second type of supernova, called a core-collapse supernova [Type II], starts out as a giant star about eight times as massive as the sun. These stars burn first through the lighter elements and then the heavier ones, fusing the lighter into heavier materials as it goes, until what remains is a nickel-iron core, which cannot be fused further, and an envelope of lighter elements surrounding it. Unable to withstand its own gravitational pull, the star collapses inward and, in a matter of seconds, rebounds with an enormous shockwave. By the time this type of supernova fully expires, all the mass of its core, equivalent to that of about one or two suns, is squeezed into a ball the size of Manhattan.

    When it goes off, it’s as luminous as entire galaxy. Should one soon go off in our own galaxy, it would be that much more—wait for it—illuminating. Scientists would amass far more and far more detailed data from a supernova explosion that was, say, a mere 20,000 light-years away than from their faraway counterparts.

    “It’s a once-in-a-lifetime chance to get exquisite data to help us understand the thousands of observed supernovae at greater distances,” Beacom says.

    It would be like bringing a distant supernova under a microscope. Scientists could better measure the dust formation that hints at how the star formed; home in on the size and brightness of the stars that give birth to the eventual supernovae; and obtain a higher-resolution picture of the star—a neutron star or a black hole—that’s left behind once the supernova lights go out.

    It’s also a chance to glimpse the interior of a star. A core-collapse supernova gives off a 10-second burst of neutrinos. The slippery particles known for being able to pass through the densest material are the first to escape. It’s a razor-thin window for something one waits for decades to observe. Scientists at neutrino detectors around the globe are at the ready for such an occurrence, networked so that one group can alert the rest of the world when its detector has seen the blink-and-you-miss-them supernova neutrinos.

    “It’s like standing out in far right field. Nothing is happening for hours. And all of a sudden there’s going to be a couple-of-second window when the ball is coming your way and you have to be there,” Beacom says. “That’s the same thing that’s happening with a Milky Way supernova, except it’s 20 or 30 years in the outfield.”

    Scientists understand fairly well how neutrinos made in our Earthly laboratories shift from one of their three types into another, a behavior called oscillation. But the neutrinos escaping supernovae, because of the star’s unimaginable density, would be incredibly closely packed together, scientists believe. Having to rub shoulders in such compact quarters might influence how they oscillate, and that oscillation could only be measured when a supernova occurs.

    If scientists were to observe this collective neutrino mixing, as it’s called, it could sew up the nagging problem of ordering the masses of the three known types of neutrinos. This, in turn, would help answer the question of whether the neutrino is its own antiparticle and how it relates to the universe’s matter-antimatter imbalance.

    Neutrinos born in a supernova could also point scientists in the direction of a black hole. If scientists observe a burst of neutrinos that, rather than petering out, is suddenly cut off, it could be a sign that the formation of a black hole has just shut the door on any more neutrinos escaping.

    “It’s not really known how often that happens and what the conditions are for that to happen, but it probably happens some of the time,” says Duke University’s Kate Scholberg, who spearheaded the supernova neutrino alert network. “There would be an abrupt cutoff of the neutrino flux. You’d see neutrinos and then, bam! There’d be no neutrinos. That would be extremely cool to see.”

    Neutrino experiments Borexino and LVD in Italy, IceCube at the South Pole and KamLAND and Super-Kamiokande in Japan would be especially excited to see such an event. If the supernova produced gravitational waves—thus far undetected ripples in space-time—detectors such as the US-based LIGO detectors might be able to pick them up.

    The sighting of a nearby supernova could better bring the science of stars down to Earth. Scientists know that many of elements we’re familiar with are forged in a supernova, up to and including iron, the heaviest known to form there. But they have no proof of where weightier stuff, such as gold and lead, originate.

    Scientists would be ecstatic to witness a supernova, but there are a few outside the scientific community who, fearing it would mean the end of the world, would be happy if a nearby star could put off its blazing demise as long as possible. While not completely baseless, such worries are easily allayed. To have any major impact on our planet, a star would have to expire as a supernova within 30 light-years of Earth. Betelgeuse, the nearest known candidate to turn supernova, is 33,000 light-years away.

    “That’s a pretty safe distance,” Scholberg says. “I don’t think we have to worry about that.”

    betelgeuse

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.



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  • richardmitnick 2:41 pm on June 27, 2014 Permalink | Reply
    Tags: , , , , , Supernovas   

    From Fermilab- “Frontier Science Result: DES Dark Energy Survey discovers exotic type of supernova 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Friday, June 27, 2014
    Chris D’Andrea and Andreas Papadopoulos, Institute of Cosmology and Gravitation, University of Portsmouth

    The first images taken by the Dark Energy Survey after it began in August 2013 have revealed a rare, “superluminous” supernova (SLSN) that erupted in a galaxy 7.8 billion light-years away. The stellar explosion, called DES13S2cmm, easily outshines most galaxies in the universe and could still be seen in the data six months later, at the end of the first of what will be five years of observing by DES.

    Dark Energy Camera
    DEcam

    night
    The Milky Way rises over the Cerro Tololo Inter-American Observatory in northern Chile. The Dark Energy Survey operates from the largest telescope at the observatory, the 4-meter Victor M. Blanco Telescope (left). Photo courtesy of Andreas Papadopoulos

    CTIO Victor M Blanco Terlescope
    CTIO Blanco

    t1as
    A Type 1a Supernova.RS Ophiuchi binary system shortly after the white dwarf (right) has exploded as a nova. The other star is a red giant. Note the spiral dust lanes. Image Credit: Casey Reed

    Supernovae are very bright, shining anywhere from 100 million to a few billion times brighter than the sun for weeks on end. Thousands of these brilliant stellar deaths have been discovered over the last two decades, and the word “supernova” itself was coined 80 years ago. Type Ia supernovae, the most well-known class of supernovae, are used by cosmologists to measure the expansion rate of the universe.

    But SLSNe are a recent discovery, recognized as a distinct class of objects only in the past five years. Although they are 10 to 50 times brighter at their peak than type Ia supernovae, fewer than 50 have ever been found. Their rareness means each new discovery brings the potential for greater understanding — or more surprises.

    It turns out that even within this select group of SLSNe, DES13S2cmm is unusual. The rate at which it is fading away over time is much slower than for most other SLSNe that have been observed to date. This change in brightness over time, or light curve, gives information on the mechanisms that caused the explosion and the composition of the material ejected. DES can constrain the potential energy source for DES13S2cmm thanks to the exceptional photometric data quality available. Only about 10 SLSNe are known that have been similarly well-studied.

    Although they are believed to come from the death of massive stars, the explosive origin of SLSNe remains a mystery. The DES team tried to explain the luminosity of DES13S2cmm as a result of the decay of the radioactive isotope nickel-56, known to power normal supernovae. They found that, to match the peak brightness, the explosion would need to produce more than three times the mass of our sun of the element. However, the model is then unable to reproduce the rate at which DES13S2cmm brightened and faded.

    A model that is more highly favored in the literature for SLSNe involves a magnetar: a neutron star that rotates once every millisecond and generates extreme magnetic fields. Produced as the remnant of a massive supernova, the magnetar begins to “spin down” and inject energy into the supernova, making the supernova exceptionally bright. This model is better able to produce the behavior of DES13S2cmm, although neither scenario could be called a good fit to the data.

    DES13S2cmm was the only confirmed SLSN from the first season of DES, but several other promising candidates were found that could not be confirmed at the time. More are expected in the coming seasons. The goal is to discover and monitor enough of these rare objects to enable them to be understood as a population.

    Although designed for studying the evolution of the universe, DES will be a powerful probe for understanding superluminous supernovae.

    See the full article here.

    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.


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