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  • 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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  • 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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  • richardmitnick 5:41 pm on May 1, 2014 Permalink | Reply
    Tags: , , , , , Supernovas   

    From Caltech: “To Supernova or Not to Supernova: A 3-D Model of Stellar Core Collapse” 

    Caltech Logo
    Caltech

    05/01/2014
    Cynthia Eller

    What happens when massive stars collapse? One potential result is a core-collapse supernova. Astronomers can make observations of such events that tell us what is happening on the surface of a star when it explodes in a supernova, but it is considerably more difficult to know what is driving the process inside the star at its hot, dense core.

    star
    A massive stellar core not quite managing to transition to a supernova explosion because of a small “kink” instability in its rotational axis.Credit: Philipp Mösta and Sherwood Richers

    Astrophysicists attempt to simulate these events based on the properties of different kinds of stars and knowledge of the fundamental interactions of mass and energy, hopefully providing astronomers with ready predictions that can be tested with observational data.

    In a recent publication, Caltech postdoctoral scholar Philipp Mösta and Christian Ott, professor of theoretical astrophysics, present a three-dimensional model of a rapidly rotating star with a strong magnetic field undergoing the process of collapse and explosion . . . or at least trying to.

    Stars with a very rapid spin and a strong magnetic field are comparatively rare: no more than one in a hundred massive stars (those at least 10 times the mass of our sun) have these features. According to Mösta and Ott’s research, when these bodies undergo core collapse, small perturbations around its axis of rotation may inhibit the process that would ordinarily lead to a supernova explosion.

    Previous models of the collapse of rapidly rotating magnetized stellar cores assumed perfect symmetry around the axis of rotation. In effect, these models were two-dimensional. The models yielded the expectation that as these cores collapsed, the strong magnetic field combined with the rapid spin would squeeze the stellar material out into two narrow “jets” along the axis of symmetry, as shown [below].

    core

    Assuming perfect symmetry around the axis of rotation can be excused in part as a matter of simplifying the scenario so that it could be simulated on an ordinary computer rather than the kind of supercomputer that Mösta and Ott’s three-dimensional simulations require: 20,000 processors to output 500 terabytes—over 500 trillion bytes—of data that represent only some 200 milliseconds in time. But, says Ott, “Even working with paper and pencil, writing down equations and discussing them with other theoretical astrophysicists, we should have known that small perturbations can trigger an instability in the stellar core. Nothing in nature is perfect. As we learn from this model, even small asymmetries can have a dramatic effect on the process of stellar collapse and the subsequent supernova explosion.

    stars

    “When Mösta and Ott took on the ambitious task of simulating a magnetorotational core collapse in three dimensions, they introduced a small asymmetry into their initial conditions: a 1 percent perturbation (a kink) around the axis of symmetry. “You can think of it like the vertebrae in your spine,” says Ott. “If one vertebra is slightly offset, there will be greater pressure on one side of the spinal column, and less pressure on the other side. This causes the disk and the material between the vertebrae to be squeezed toward the side with less pressure. The same thing happens when you introduce a kink in the axis of symmetry of a collapsing star with a strong magnetic field.”

    With an ever-so-slightly distorted magnetic field, the core is still constrained in the middle, just as it is in the axially symmetric model. But instead of producing two perfectly matched jets, the magnetic distortion—it is called a “kink instability”—produces two asymmetric, misshapen lobes, as shown at right. “Even more noteworthy,” says Mösta, “is the fact that in the three-dimensional model, the explosion—the supernova—never quite gets off the ground.

    This slideshow illustrates the three-dimensional simulation in a step-by-step fashion.

    Setting the two simulations—two-dimensional and three-dimensional—alongside one another provide a dramatic visualization of the impact of even a small asymmetry in a rapidly-rotating, magnetized body. In a video that compares the two, 186 milliseconds of core collapse are slowed to fill two minutes of real time. The two events look very similar for about 20 milliseconds, before the kink instability in the three-dimensional model begins to deform the stellar core and constrain its progress toward supernova.

    The kink instability in the three-dimensional simulation leads to a “wobbling” of the central funnel of material that is pushed out by the ultra-dense and hot stellar core, a proto-neutron star. “As the material expands, it gets wound in tubes around the spin axis of the star, like water being expelled vigorously from a garden hose left lying on the ground,” says Mösta. In the three-dimensional view illustrated here, regions in which the magnetic field pressure dominates are yellow, while regions that are dominated by the normal pressure of the stellar gas are blue, red, and black.

    unstable

    Unlike the two-dimensional, axially symmetric simulations with their uniform jets along the axis of rotation, the three-dimensional simulations of Mösta and Ott result in two lobes of twisted and highly magnetized material that are only slowly pushed outward and do not show signs of a runaway explosion at the end of the simulation. More and longer simulations on more powerful supercomputers will be needed to determine the final fate of core collapse in a rapidly rotating magnetized star.

    “We can be smarter in our simulations now,” says Ott. “We are wrestling with a more interesting if less perfect universe—the one we actually live in.”

    The paper, Magnetorotational Core-collapse Supernovae in Three Dimensions, appeared in the April 3, 2014, issue of Astrophysical Journal Letters and is authored by Mösta, Ott, Sherwood Richers, Roland Haas, Anthony Piro, Kristen Boydstun, Ernazar Abdikamalov, and Christian Reisswig, all of Caltech, and Erik Schnetter of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada. This research was funded by the National Science Foundation, the Sherman Fairchild Foundation, the U.S. Department of Energy, and NASA.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 3:58 pm on February 19, 2014 Permalink | Reply
    Tags: , , , , , Supernovas   

    From NASA/NuSTAR: “NASA’s NuSTAR Untangles Mystery of How Stars Explode” 

    NASA NuSTAR
    NuSTAR

    One of the biggest mysteries in astronomy, how stars blow up in supernova explosions, finally is being unraveled with the help of NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR).

    The high-energy X-ray observatory has created the first map of radioactive material in a supernova remnant. The results, from a remnant named Cassiopeia A (Cas A), reveal how shock waves likely rip apart massive dying stars.

    Cas A
    Untangling the Remains of Cassiopeia A.
    This is the first map of radioactivity in a supernova remnant, the blown-out bits and pieces of a massive star that exploded. The blue color shows radioactive material mapped in high-energy X-rays using NuSTAR. Image credit: NASA/JPL-Caltech/CXC/SAO

    cas a 2
    Adding a New ‘Color’ to Palate of Cassiopeia A Images
    NuSTAR is complementing previous observations of the Cassiopeia A supernova remnant (red and green) by providing the first maps of radioactive material forged in the fiery explosion (blue). Image credit: NASA/JPL-Caltech/CXC/SAO

    new
    Radioactive Core of a Dead Star
    NuSTAR has, for the first time, imaged the radioactive “guts” of a supernova remnant, the leftover remains of a star that exploded. Image credit: NASA/JPL-Caltech/CXC/SAO

    cas a 3
    The Case of Missing Iron in Cassiopeia A
    When astronomers first looked at images of a supernova remnant called Cassiopeia A, captured by NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, they were shocked. Image credit: NASA/JPL-Caltech/CXC/SAO

    three
    Evolution of a Supernova
    These illustrations show the progression of a supernova blast. A massive star (left), which has created elements as heavy as iron in its interior, blows up in a tremendous explosion (middle), scattering its outer layers in a structure called a supernova remnant (right). Image credit: NASA/CXC/SAO/JPL-Caltech

    four
    NuSTAR Data Point to Sloshing Supernovas
    Two popular models describing how massive stars explode are shown in the top two panels. Image credit: NASA/JPL-Caltech/CXC/SAO/SkyWorks Digital/Christian Ott

    “Stars are spherical balls of gas, and so you might think that when they end their lives and explode, that explosion would look like a uniform ball expanding out with great power,” said Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology (Caltech) in Pasadena. “Our new results show how the explosion’s heart, or engine, is distorted, possibly because the inner regions literally slosh around before detonating.”

    Harrison is a co-author of a paper about the results appearing in the Feb. 20 issue of Nature.

    Cas A was created when a massive star blew up as a supernova, leaving a dense stellar corpse and its ejected remains. The light from the explosion reached Earth a few hundred years ago, so we are seeing the stellar remnant when it was fresh and young.

    Supernovas seed the universe with many elements, including the gold in jewelry, the calcium in bones and the iron in blood. While small stars like our sun die less violent deaths, stars at least eight times as massive as our sun blow up in supernova explosions. The high temperatures and particles created in the blast fuse light elements together to create heavier elements.

    NuSTAR is the first telescope capable of producing maps of radioactive elements in supernova remnants. In this case, the element is titanium-44, which has an unstable nucleus produced at the heart of the exploding star.

    The NuSTAR map of Cas A shows the titanium concentrated in clumps at the remnant’s center and points to a possible solution to the mystery of how the star met its demise. When researchers simulate supernova blasts with computers, as a massive star dies and collapses, the main shock wave often stalls out and the star fails to shatter. The latest findings strongly suggest the exploding star literally sloshed around, re-energizing the stalled shock wave and allowing the star to finally blast off its outer layers.

    “With NuSTAR we have a new forensic tool to investigate the explosion,” said the paper’s lead author, Brian Grefenstette of Caltech. “Previously, it was hard to interpret what was going on in Cas A because the material that we could see only glows in X-rays when it’s heated up. Now that we can see the radioactive material, which glows in X-rays no matter what, we are getting a more complete picture of what was going on at the core of the explosion.”

    The NuSTAR map also casts doubt on other models of supernova explosions, in which the star is rapidly rotating just before it dies and launches narrow streams of gas that drive the stellar blast. Though imprints of jets have been seen before around Cas A, it was not known if they were triggering the explosion. NuSTAR did not see the titanium, essentially the radioactive ash from the explosion, in narrow regions matching the jets, so the jets were not the explosive trigger.

    “This is why we built NuSTAR,” said Paul Hertz, director of NASA’s astrophysics division in Washington. “To discover things we never knew – and did not expect – about the high-energy universe.”

    The researchers will continue to investigate the case of Cas A’s dramatic explosion. Centuries after its death marked our skies, this supernova remnant continues to perplex.

    For more information about NuSTAR and images, visit: http://www.nasa.gov/nustar

    See the full article here.

    NuSTAR is a Small Explorer mission led by the California Institute of Technology in Pasadena and managed by NASA’s Jet Propulsion Laboratory, also in Pasadena, for NASA’s Science Mission Directorate in Washington. The spacecraft was built by Orbital Sciences Corporation, Dulles, Va. Its instrument was built by a consortium including Caltech; JPL; the University of California, Berkeley ; Columbia University, New York; NASA’s Goddard Space Flight Center, Greenbelt, Md.; the Danish Technical University in Denmark; Lawrence Livermore National Laboratory, Livermore, Calif.; ATK Aerospace Systems, Goleta, Calif., and with support from the Italian Space Agency (ASI) Science Data Center.

    NuSTAR’s mission operations center is at UC Berkeley, with the ASI providing its equatorial ground station located at Malindi, Kenya. The mission’s outreach program is based at Sonoma State University, Rohnert Park, Calif. NASA’s Explorer Program is managed by Goddard. JPL is managed by Caltech for NASA.

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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  • richardmitnick 12:22 pm on September 26, 2013 Permalink | Reply
    Tags: , , , , , Supernovas   

    From NASA/Chandra: “Tycho’s Supernova Remnant: NASA’S Chandra Finds New Evidence on Origin of Supernovas” 

    NASA Chandra

    An arc of emission just found in the Tycho supernova remnant provides evidence for what triggered the original explosion. Astronomers think that a shock wave created the arc when a white dwarf exploded and blew material off the surface of a nearby companion star. Tycho belongs to a category of supernovas that are used to measure the expansion of the Universe.

    comp
    Composite

    low
    Low

    med
    Medium

    high
    High
    Credit NASA/CXC/Chinese Academy of Sciences/F. Lu et al
    Release Date April 26, 2011

    This new image of Tycho’s supernova remnant, dubbed Tycho for short, contains striking new evidence for what triggered the original supernova explosion, as seen from Earth in 1572. Tycho was formed by a Type Ia supernova, a category of stellar explosion used in measuring astronomical distances because of their reliable brightness.

    Low and medium energy X-rays in red and green show expanding debris from the supernova explosion. High energy X-rays in blue reveal the blast wave, a shell of extremely energetic electrons. Also shown in the lower left region of Tycho is a blue arc of X-ray emission. Several lines of evidence support the conclusion that this arc is due to a shock wave created when a white dwarf exploded and blew material off the surface of a nearby companion star (see accompanying illustration below). Previously, studies with optical telescopes have revealed a star within the remnant that is moving much more quickly than its neighbors, hinting that it could be the companion to the supernova that was given a kick by the explosion.

    map

    Other details of the arc support the idea that it was blasted away from the companion star. For example, the X-ray emission of the remnant shows an apparent “shadow” next to the arc, consistent with the blocking of debris from the explosion by the expanding cone of material stripped from the companion. This shadow is most obvious in very high energy X-rays showing iron debris.

    These pieces of evidence support a popular scenario for triggering a Type Ia supernova, where a white dwarf pulls material from a “normal,” or Sun-like, companion star until a thermonuclear explosion occurs. In the other main competing theory, a merger of two white dwarfs occurs, and in this case, no companion star or evidence for material blasted off a companion, should exist. Both scenarios may actually occur under different conditions, but the latest Chandra result from Tycho supports the former one.

    The shape of the arc is different from any other feature seen in the remnant. Other features in the interior of the remnant include recently announced stripes, which have a different shape and are thought to be features in the outer blast wave caused by cosmic ray acceleration.

    See the full article here.

    Chandra X-ray Center, Operated for NASA by the Smithsonian Astrophysical Observatory
    Smithsonian Astrophysical Observatory


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  • richardmitnick 7:15 am on April 3, 2013 Permalink | Reply
    Tags: , , , , , Supernovas   

    From NASA/ESA Hubble: “Hubblecast 64: It all ends with a bang!” 

    This is a very worthwhile video from NASA/ESA Hubble, with host “Dr J”, a.k.a Dr Joe Liske. The video is all about supernovae .

    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.


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