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  • richardmitnick 11:30 am on November 28, 2019 Permalink | Reply
    Tags: "The Secret History of the Supernova at the Bottom of the Sea", , , , , , Fe-60 a heavy isotope of iron with four more neutrons than the regular isotope, Ferromanganese crusts, , SN 1987A announced the violent collapse of a massive star., Supernovas   

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

    Nautilus

    From Nautilus

    November 28, 2019
    Julia Rosen

    1
    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

    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.

    SN1987a from NASA/ESA Hubble Space Telescope in Jan. 2017 using its Wide Field Camera 3 (WFC3).

    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.

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    Plain-looking, but important: Ferromanganese crusts collected by James 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 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 the 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 centimeters 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 7 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.

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    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 Knie’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.

    See the full article here .

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 7:09 am on April 16, 2018 Permalink | Reply
    Tags: , , , , , , Supernovas   

    From NASA Chandra via Manu: “MSH 11-62 and G327.1-1.1: Supernova Shock Waves, Neutron Stars, and Lobsters” November 19, 2014 


    Manu Garcia, a friend from IAC.

    The universe around us.
    Astronomy, everything you wanted to know about our local universe and never dared to ask.

    NASA Chandra Banner

    NASA/Chandra Telescope


    NASA Chandra

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    Credit NASA/CXC/GSFC/T.Temim et al.

    Two new Chandra images of supernova remnants reveal intricate structures left behind after massive stars exploded.

    Powerful winds of high-energy particles are released from the dense core of the dead star to create so-called pulsar wind nebulas.

    MSH 11-62 and G327.1-1.1 are examples of how complex the aftermath of stellar explosions can be.

    A supernova that signals the death of a massive star sends titanic shock waves rumbling through interstellar space. An ultra-dense neutron star is usually left behind, which is far from dead, as it spews out a blizzard of high-energy particles.

    Two new images from NASA’s Chandra X-ray Observatory provide fascinating views — including an enigmatic lobster-like feature — of the complex aftermath of a supernova.

    When a massive star runs out of fuel resulting in a supernova explosion, the central regions usually collapse to form a neutron star. The energy generated by the formation of the neutron star triggers a supernova. As the outward-moving shock wave sweeps up interstellar gas, a reverse shock wave is driven inward, heating the stellar ejecta.

    Meanwhile, the rapid rotation and intense magnetic field of the neutron star, a.k.a. a pulsar, combine to generate a powerful wind of high-energy particles. This so-called pulsar wind nebula can glow brightly in X-rays and radio waves.

    A long observation with Chandra of the supernova remnant MSH 11-62 (left image) reveals an irregular shell of hot gas, shown in red, surrounding an extended nebula of high energy X-rays, shown in blue. Even though scientists have yet to detect any pulsations from the central object within MSH 11-62, the structure around it has many of the same characteristics as other pulsar wind nebulas. The reverse shock and other, secondary shocks within MSH 11-62 appear to have begun to crush the pulsar wind nebula, possibly contributing to its elongated shape. (Note: the orientation of this image has been rotated by 24 degrees so that north is pointed to the upper left.)

    MSH 11-62 is located about 16,000 light years from Earth. The foreground of MSH 11-62 is speckled with hundreds of sources associated with the open stellar cluster Trumpler 18, located at a distance of about 5,000 light years, revealing a vast collection of stars.

    The supernova remnant G327.1-1.1, located about 29,000 light years from Earth, is another spectacular debris field left behind when a massive star exploded. The Chandra image of G327.1-1.1 (right image) shows the outward-moving, or forward, shock wave (seen as the faint red color), and a bright pulsar wind nebula (blue). The pulsar wind nebula appears to have been distorted by the combined action of the reverse shock wave, which may have flattened it, and by the motion of the pulsar, which created a comet, or lobster-like tail. An asymmetric supernova explosion may have given a recoil kick to the pulsar, causing it to move rapidly and drag the pulsar wind nebula along with it.

    Two structures resembling lobster claws protrude from near the head of the pulsar wind nebula. The origin of these features, which may be produced by the interaction of the pulsar wind with the reverse shock, is unknown.

    These results are presented at the “15 Years of Chandra” symposium (http://cxc.harvard.edu/symposium_2014/) by Patrick Slane of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., and Tea Temim of NASA’s Goddard Space Flight Center, Greenbelt, Md.

    See the full article here .

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    NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.

     
  • richardmitnick 5:09 pm on December 26, 2017 Permalink | Reply
    Tags: 'Direct Collapse' Black Holes May Explain Our Universe's Mysterious Quasars, , , , , , , , , , Star formation is a violent process, , Supernovas   

    From Ethan Siegel: “‘Direct Collapse’ Black Holes May Explain Our Universe’s Mysterious Quasars” 

    From Ethan Siegel
    Dec 26, 2017

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    The most distant X-ray jet in the Universe, from quasar GB 1428, is approximately the same distance and age, as viewed from Earth, as quasar S5 0014+81; both are over 12 billion light years away. X-ray: NASA/CXC/NRC/C.Cheung et al; Optical: NASA/STScI; Radio: NSF/NRAO/VLA

    NASA/Chandra Telescope


    NASA/ESA Hubble Telescope


    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    There’s a big problem when we look at the brightest, most energetic objects we can see in the early stages of the Universe. Shortly after the first stars and galaxies form, we find the first quasars: extremely luminous sources of radiation that span the electromagnetic spectrum, from radio up through the X-ray. Only a supermassive black hole could possibly serve as the engine for one of these cosmic behemoths, and the study of active objects like quasars, blazars, and AGNs all support this idea. But there’s a problem: it may not be possible to make a black hole so large, so quickly, to explain these young quasars that we see. Unless, that is, there’s a new way to make black holes beyond what we previously thought. This year, we found the first evidence for a direct collapse black hole, and it may lead to the solution we’ve sought for so long.

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    While distant host galaxies for quasars and active galactic nuclei can often be imaged in visible/infrared light, the jets themselves and the surrounding emission is best viewed in both the X-ray and the radio, as illustrated here for the galaxy Hercules A. It takes a black hole to power an engine such as this. NASA, ESA, S. Baum and C. O’Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA).

    Generically known as ‘active galaxies,’ almost all galaxies posses supermassive black holes at their center, but only a few emit the intense radiation associated with quasars or AGNs. The leading idea is that supermassive black holes will feed on matter, accelerating and heating it, which causes it to ionize and give off light. Based on the light we observe, we can successfully infer the mass of the central black hole, which often reaches billions of times the mass of our Sun. Even for the earliest quasars, such as J1342+0928, we can get up to a mass of 800 million solar masses just 690 million years after the Big Bang: when the Universe was just 5% of its current age.

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    This artist’s concept shows the most distant supermassive black hole ever discovered. It is part of a quasar from just 690 million years after the Big Bang. Robin Dienel/Carnegie Institution for Science.

    If you try to build a black hole in the conventional way, by having massive stars go supernova, form small black holes, and have them merge together, you run into problems. Star formation is a violent process, as when nuclear fusion ignites, the intense radiation burns off the remaining gas that would otherwise go into forming progressively more and more massive stars. From nearby star-forming regions to the most distant ones we’ve ever observed, this same process seems to be in place, preventing stars (and, hence, black holes) beyond a certain mass from ever forming.

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    An artist’s conception of what the Universe might look like as it forms stars for the first time. While stars might reach many hundreds or even a thousand solar masses, it’s very difficult to see how you could get a black hole of the mass the earliest quasars are known to possess. NASA/JPL-Caltech/R. Hurt (SSC).

    We have a standard scenario that’s very powerful and compelling: of supernova explosions, gravitational interactions, and then growth by mergers and accretion. But the early quasars we see are too massive too quickly to be explained by this. Our other known pathway to create black holes, from merging neutron stars, provides no further help. Instead, a third scenario of direct collapse may be responsible. This idea has been helped along by three pieces of evidence in the past year:

    1.The discovery of ultra-young quasars like J1342+0928, in possession of black holes many hundred of millions of solar masses.
    2.Theoretical advances that show how, if the direct collapse scenario is true, we could form early “seed” black holes a thousand times as massive as the ones formed by supernova.
    3.And the discovery of the first stars that become black holes via direct collapse, validating the process.

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    In addition to formation by supernovae and neutron star mergers, it should be possible for black holes to form via direct collapse. Simulations such as the one shown here demonstrate that, under the right condition, seed black holes of 100,000 to 1,000,000 solar masses could form in the very early stages of the Universe. Aaron Smith/TACC/UT-Austin.

    Normally, it’s the hottest, youngest, most massive, and newest stars in the Universe that will lead to a black hole. There are plenty of galaxies like this in the early stages of the Universe, but there are also plenty of proto-galaxies that are all gas, dust, and dark matter, with no stars in them yet. Out in the great cosmic abyss, we’ve even found an example of a pair of galaxies just like this: where one has furiously formed stars and the other one may not have formed any yet. The ultra-distant galaxy, known as CR7, has a massive population of young stars, and a nearby patch of light-emitting gas that may not have yet formed a single star in it.

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    Illustration of the distant galaxy CR7, which last year was discovered to house a pristine population of stars formed from the material direct from the Big Bang. One of these galaxies definitely houses stars; the other may not have formed any yet. M. Kornmesser / ESO.

    In a theoretical study published in March [Nature Astronomy] of this year, a fascinating mechanism for producing direct collapse black holes from a mechanism like this was introduced. A young, luminous galaxy could irradiate a nearby partner, which prevents the gas within it from fragmenting to form tiny clumps. Normally, it’s the tiny clumps that collapse into individual stars, but if you fail to form those clumps, you instead can just get a monolithic collapse of a huge amount of gas into a single bound structure. Gravitation then does its thing, and your net result could be a black hole over 100,000 times as massive as our Sun, perhaps even all the way up to 1,000,000 solar masses.

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    Distant, massive quasars show ultramassive black holes in their cores. It’s very difficult to form them without a large seed, but a direct collapse black hole could solve that puzzle quite elegantly. J. Wise/Georgia Institute of Technology and J. Regan/Dublin City University.

    There are many theoretical mechanisms that turn out to be intriguing, however, that aren’t borne out when it comes to real, physical environments. Is direct collapse possible? We can now definitively answer that question with a “yes,” as the first star that was massive enough to go supernova was seen to simply wink out of existence. No fireworks; no explosion; no increase in luminosity. Just a star that was there one moment, and replaces with a black hole the next. As spotted before-and-after with Hubble, there is no doubt that the direct collapse of matter to a black hole occurs in our Universe.

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    The visible/near-IR photos from Hubble show a massive star, about 25 times the mass of the Sun, that has winked out of existence, with no supernova or other explanation. Direct collapse is the only reasonable candidate explanation. NASA/ESA/C. Kochanek (OSU).

    Put all three of these pieces of information together, and you arrive at the following picture for how these supermassive black holes form so early.

    A region of space collapses to form stars, while a nearby region of space has also undergone gravitational collapse but hasn’t formed stars yet.
    The region with stars emits an intense amount of radiation, where the photon pressure keeps the gas in the other cloud from fragmenting into potential stars.
    The cloud itself continues to collapse, doing so in a monolithic fashion. It expels energy (radiation) as it does so, but without any stars inside.
    When a critical threshold is crossed, that huge amount of mass, perhaps hundreds of thousands or even millions of times the mass of our Sun, directly collapses to form a black hole.
    From this massive, early seed, it’s easy to get supermassive black holes simply by the physics of gravitation, merger, accretion, and time.

    It might not only be possible, but with the new array of radio telescopes coming online, as well as the James Webb Space Telescope, we may be able to witness the process in action.

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

    SKA Square Kilometer Array


    SKA/ASKAP radio telescope at the Murchison Radio-astronomy Observatory (MRO) in Mid West region of Western Australia


    SKA Murchison Widefield Array, Boolardy station in outback Western Australia, at the Murchison Radio-astronomy Observatory (MRO)

    The galaxy CR7 is likely one example of many similar objects likely to be out there. As Volker Bromm, the theorist behind the direct collapse mechanism first said [RAS], a nearby, luminous galaxy could cause a nearby cloud of gas to directly collapse. All you need to do is begin with a

    “primordial cloud of hydrogen and helium, suffused in a sea of ultraviolet radiation. You crunch this cloud in the gravitational field of a dark-matter halo. Normally, the cloud would be able to cool, and fragment to form stars. However, the ultraviolet photons keep the gas hot, thus suppressing any star formation. These are the desired, near-miraculous conditions: collapse without fragmentation! As the gas gets more and more compact, eventually you have the conditions for a massive black hole.”

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    The directly collapsing star we observed exhibited a brief brightening before having its luminosity drop to zero, an example of a failed supernova. For a large cloud of gas, the luminous emission of light is expected, but no stars are necessary to form a black hole this way.
    NASA/ESA/P. Jeffries (STScI)

    With a little luck, by time 2020 rolls around, this is one longstanding mystery that might finally be solved.

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 5:34 pm on December 10, 2017 Permalink | Reply
    Tags: , , , , , , , , NASA's SuperTIGER Balloon Flies Again to Study Heavy Cosmic Particles, , Supernovas   

    From Goddard: “NASA’s SuperTIGER Balloon Flies Again to Study Heavy Cosmic Particles” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    Dec. 6, 2017
    Francis Reddy
    francis.j.reddy@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    A science team in Antarctica is preparing to loft a balloon-borne instrument to collect information on cosmic rays, high-energy particles from beyond the solar system that enter Earth’s atmosphere every moment of every day. The instrument, called the Super Trans-Iron Galactic Element Recorder (SuperTIGER), is designed to study rare heavy nuclei, which hold clues about where and how cosmic rays attain speeds up to nearly the speed of light.

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    NASA’s Super-TIGER balloon

    The launch is expected by Dec. 10, weather permitting.

    1
    Explore this infographic [on the full article] to learn more about SuperTIGER, cosmic rays and scientific ballooning.
    Credits: NASA’s Goddard Space Flight Center

    Download infographic as PDF

    “The previous flight of SuperTIGER lasted 55 days, setting a record for the longest flight of any heavy-lift scientific balloon,” said Robert Binns, the principal investigator at Washington University in St. Louis, which leads the mission. “The time aloft translated into a long exposure, which is important because the particles we’re after make up only a tiny fraction of cosmic rays.”

    The most common cosmic ray particles are protons or hydrogen nuclei, making up roughly 90 percent, followed by helium nuclei (8 percent) and electrons (1 percent). The remainder contains the nuclei of other elements, with dwindling numbers of heavy nuclei as their mass rises. With SuperTIGER, researchers are looking for the rarest of the rare — so-called ultra-heavy cosmic ray nuclei beyond iron, from cobalt to barium.

    “Heavy elements, like the gold in your jewelry, are produced through special processes in stars, and SuperTIGER aims to help us understand how and where this happens,” said lead co-investigator John Mitchell at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We’re all stardust, but figuring out where and how this stardust is made helps us better understand our galaxy and our place in it.”

    When a cosmic ray strikes the nucleus of a molecule of atmospheric gas, both explode in a shower of subatomic shrapnel that triggers a cascade of particle collisions. Some of these secondary particles reach detectors on the ground, providing information scientists can use to infer the properties of the original cosmic ray. But they also produce an interfering background that is greatly reduced by flying instruments on scientific balloons, which reach altitudes of nearly 130,000 feet (40,000 meters) and float above 99.5 percent of the atmosphere.

    The most massive stars forge elements up to iron in their cores and then explode as supernovas, dispersing the material into space. The explosions also create conditions that result in a brief, intense flood of subatomic particles called neutrons. Many of these neutrons can “stick” to iron nuclei. Some of them subsequently decay into protons, producing new elements heavier than iron.

    Supernova blast waves provide the boost that turns these particles into high-energy cosmic rays.

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    NASA’s Fermi Proves Supernova Remnants Produce Cosmic Rays. February 14, 2013.

    NASA/Fermi Telescope


    NASA/Fermi LAT


    As a shock wave expands into space, it entraps and accelerates particles until they reach energies so extreme they can no longer be contained.

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    On Dec. 1, SuperTIGER was brought onto the deck of Payload Building 2 at McMurdo Station, Antarctica, to test communications in preparation for its second flight. Mount Erebus, the southernmost active volcano on Earth, appears in the background.
    Credits: NASA/Jason Link

    Over the past two decades, evidence accumulated from detectors on NASA’s Advanced Composition Explorer satellite and SuperTIGER’s predecessor, the balloon-borne TIGER instrument, has allowed scientists to work out a general picture of cosmic ray sources. Roughly 20 percent of cosmic rays were thought to arise from massive stars and supernova debris, while 80 percent came from interstellar dust and gas with chemical quantities similar to what’s found in the solar system.

    “Within the last few years, it has become apparent that some or all of the very neutron-rich elements heavier than iron may be produced by neutron star mergers instead of supernovas,” said co-investigator Jason Link at Goddard.

    Neutron stars are the densest objects scientists can study directly, the crushed cores of massive stars that exploded as supernovas. Neutron stars orbiting each other in binary systems emit gravitational waves, which are ripples in space-time predicted by Einstein’s general theory of relativity. These waves remove orbital energy, causing the stars to draw ever closer until they eventually crash together and merge.

    Theorists calculated that these events would be so thick with neutrons they could be responsible for most of the very neutron-rich cosmic rays heavier than nickel. On Aug. 17, NASA’s Fermi Gamma-ray Space Telescope and the National Science Foundation’s Laser Interferometer Gravitational-wave Observatory detected the first light and gravitational waves from crashing neutron stars. Later observations by the Hubble and Spitzer space telescopes indicate that large amounts of heavy elements were formed in the event.

    “It’s possible neutron star mergers are the dominant source of heavy, neutron-rich cosmic rays, but different theoretical models produce different quantities of elements and their isotopes,” Binns said. “The only way to choose between them is to measure what’s really out there, and that’s what we’ll be doing with SuperTIGER.”

    SuperTIGER is funded by the NASA Headquarters Science Mission Directorate Astrophysics Division.

    The National Science Foundation (NSF) Office of Polar Programs manages the U.S. Antarctic Program and provides logistic support for all U.S. scientific operations in Antarctica. NSF’s Antarctic support contractor supports the launch and recovery operations for NASA’s Balloon Program in Antarctica. Mission data were downloaded using NASA’s Tracking and Data Relay Satellite System.

    For more information about NASA’s Balloon Program, visit:

    http://www.nasa.gov/balloons

    See the full article here.

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    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.


    NASA/Goddard Campus

     
  • richardmitnick 6:51 pm on February 14, 2017 Permalink | Reply
    Tags: , , , , Caltech Palomar Intermediate Palomar Transient Factory, , Supernovas   

    From ars technica: “Observations catch a supernova three hours after it exploded” 

    Ars Technica
    ars technica

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    BRIGHT AND EARLY Scientists caught an early glimpse of an exploding star in the galaxy NGC7610 (shown before the supernova). Light from the explosion revealed that gas (orange) surrounded the star, indicating that the star spurted out gas in advance of the blast.

    2
    The remains of an earlier Type II supernova. NASA

    The skies are full of transient events. If you don’t happen to have a telescope pointed at the right place at the right time, you can miss anything from the transit of a planet to the explosion of a star. But thanks to the development of automated survey telescopes, the odds of getting lucky have improved considerably.

    In October of 2013, the telescope of the intermediate Palomar Transient Factory worked just as expected, capturing a sudden brightening that turned out to reflect the explosion of a red supergiant in a nearby galaxy.

    Caltech Palomar Intermediate Palomar Transient Factory telescope at the Samuel Oschin Telescope at Palomar Observatory,located in San Diego County, California, United States
    Caltech Palomar Intermediate Palomar Transient Factory telescope at the Samuel Oschin Telescope at Palomar Observatory,located in San Diego County, California, United States

    The first images came from within three hours of the supernova itself, and followup observations tracked the energy released as it blasted through the nearby environment. The analysis of the event was published on Monday in Nature Physics, and it suggests the explosion followed shortly after the star ejected large amounts of material.

    This isn’t the first supernova we’ve witnessed as it happened; the Kepler space telescope captured two just as the energy of the explosion of the star’s core burst through the surface. By comparison, observations three hours later are relative latecomers. But SN 2013fs (as it was later termed) provided considerably more detail, as followup observations were extensive and covered all wavelengths, from X-rays to the infrared.

    Critically, spectroscopy began within six hours of the explosion. This technique separates the light according to its wavelength, allowing researchers to identify the presence of specific atoms based on the colors of light they absorb. In this case, the spectroscopy picked up the presence of atoms such as oxygen and helium, which lost most of its electrons. The presence of these heavily ionized oxygen atoms surged for several hours, then was suddenly cut off 11 hours later.

    The authors explain this behavior by positing that the red supergiant ejected a significant amount of material before it exploded. The light from the explosion then swept through the vicinity, eventually catching up with the material and stripping the electrons off its atoms. The sudden cutoff came when the light exited out the far side of the material, allowing it to return to a lower energy state, where it stayed until the physical debris of the explosion slammed into it about five days later.

    Since the light of the explosion is moving at the speed of light (duh), we know how far away the material was: six light hours, or roughly the Sun-Pluto distance. Some blurring in the spectroscopy also indicates that it was moving at about 100 kilometers a second. Based on its speed and the distance it is from the star that ejected it, they could calculate when it was ejected: less than 500 days before the explosion. The total mass of the material also suggests that the star was losing about 0.1 percent of the Sun’s mass a year.

    Separately, the authors estimate that it is unlikely there is a single star in our galaxy with the potential to be less than 500 days from explosion, so we probably won’t be able to look at an equivalent star—assuming we knew how to identify it.

    Large stars like red supergiants do sporadically eject material, so there’s always the possibility that the ejection-explosion series occurred by chance. But this isn’t the first supernova we’ve seen where explosion material has slammed into a shell of material that had been ejected earlier. Indeed, the closest red supergiant, Betelgeuse, has a stable shell of material a fair distance from its surface.

    What could cause these ejections? For most of their relatively short lives, these giant stars are fusing relatively light elements, each of which is present in sufficient amounts to burn for millions of years. But once they start to shift to heavier elements, higher rates of fusion are needed to counteract gravity, which is constantly drawing the elements in the core. As a result, the core undergoes major rearrangements as it changes fuels, sometimes within a span of a couple of years. It’s possible, suggests an accompanying perspective by astronomer Norbert Langer, that these rearrangements propagate to the surface and force the ejection of matter.

    For now, we’ll have to explore this possibility using models of the interiors of giant stars. But with enough survey telescopes in operation, we may have more data to test the idea against before too long.

    Nature Physics, 2017. DOI: 10.1038/NPHYS4025

    See the full article here .

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    Ars Technica was founded in 1998 when Founder & Editor-in-Chief Ken Fisher announced his plans for starting a publication devoted to technology that would cater to what he called “alpha geeks”: technologists and IT professionals. Ken’s vision was to build a publication with a simple editorial mission: be “technically savvy, up-to-date, and more fun” than what was currently popular in the space. In the ensuing years, with formidable contributions by a unique editorial staff, Ars Technica became a trusted source for technology news, tech policy analysis, breakdowns of the latest scientific advancements, gadget reviews, software, hardware, and nearly everything else found in between layers of silicon.

    Ars Technica innovates by listening to its core readership. Readers have come to demand devotedness to accuracy and integrity, flanked by a willingness to leave each day’s meaningless, click-bait fodder by the wayside. The result is something unique: the unparalleled marriage of breadth and depth in technology journalism. By 2001, Ars Technica was regularly producing news reports, op-eds, and the like, but the company stood out from the competition by regularly providing long thought-pieces and in-depth explainers.

    And thanks to its readership, Ars Technica also accomplished a number of industry leading moves. In 2001, Ars launched a digital subscription service when such things were non-existent for digital media. Ars was also the first IT publication to begin covering the resurgence of Apple, and the first to draw analytical and cultural ties between the world of high technology and gaming. Ars was also first to begin selling its long form content in digitally distributable forms, such as PDFs and eventually eBooks (again, starting in 2001).

    Nature Physics, 2017. DOI: 10.1038/NPHYS4025

     
  • richardmitnick 5:34 pm on April 6, 2016 Permalink | Reply
    Tags: , , , , Supernovas   

    From phys.org: “Supernovae showered Earth with radioactive debris” 

    physdotorg
    phys.org

    April 6, 2016
    No writer credit found

    1
    Artist’s impression of supernova. Credit: Greg Stewart, SLAC National Accelerator Lab

    An international team of scientists has found evidence of a series of massive supernova explosions near our solar system, which showered the Earth with radioactive debris.

    The scientists found radioactive iron-60 in sediment and crust samples taken from the Pacific, Atlantic and Indian Oceans.

    The iron-60 was concentrated in a period between 3.2 and 1.7 million years ago, which is relatively recent in astronomical terms, said research leader Dr Anton Wallner from The Australian National University (ANU).

    “We were very surprised that there was debris clearly spread across 1.5 million years,” said Dr Wallner, a nuclear physicist in the ANU Research School of Physics and Engineering. “It suggests there were a series of supernovae, one after another.

    “It’s an interesting coincidence that they correspond with when the Earth cooled and moved from the Pliocene into the Pleistocene period.”

    The team from Australia, the University of Vienna in Austria, Hebrew University in Israel, Shimizu Corporation and University of Tokyo, Nihon University and University of Tsukuba in Japan, Senckenberg Collections of Natural History Dresden and Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany, also found evidence of iron-60 from an older supernova around eight million years ago, coinciding with global faunal changes in the late Miocene.

    Some theories suggest cosmic rays from the supernovae could have increased cloud cover.

    Cassiopeia A false color image using Hubble and Spitzer telescopes and Chandra X-ray Observatory. Credit NASA JPL-Caltech
    Cassiopeia A false color image using Hubble and Spitzer telescopes and Chandra X-ray Observatory. Credit NASA JPL-Caltech

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    NASA/Spitzer Telescope
    NASA/Spitzer Telescope

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    The scientists believe the supernovae in this case were less than 300 light years away, close enough to be visible during the day and comparable to the brightness of the Moon.

    Although Earth would have been exposed to an increased cosmic ray bombardment, the radiation would have been too weak to cause direct biological damage or trigger mass extinctions.

    The supernova explosions create many heavy elements and radioactive isotopes which are strewn into the cosmic neighbourhood.

    One of these isotopes is iron-60 which decays with a half-life of 2.6 million years, unlike its stable cousin iron-56. Any iron-60 dating from the Earth’s formation more than four billion years ago has long since disappeared.

    The iron-60 atoms reached Earth in minuscule quantities and so the team needed extremely sensitive techniques to identify the interstellar iron atoms.

    “Iron-60 from space is a million-billion times less abundant than the iron that exists naturally on Earth,” said Dr Wallner.

    Dr Wallner was intrigued by first hints of iron-60 in samples from the Pacific Ocean floor, found a decade ago by a group at TU Munich.

    He assembled an international team to search for interstellar dust from 120 ocean-floor samples spanning the past 11 million years.

    The first step was to extract all the iron from the ocean cores. This time-consuming task was performed by two groups, at HZDR and the University of Tokyo.

    The team then separated the tiny traces of interstellar iron-60 from the other terrestrial isotopes using the Heavy-Ion Accelerator at ANU and found it occurred all over the globe.

    The age of the cores was determined from the decay of other radioactive isotopes, beryllium-10 and aluminium-26, using accelerator mass spectrometry (AMS) facilities at DREsden AMS (DREAMS) of HZDR, Micro Analysis Laboratory (MALT) at the University of Tokyo and the Vienna Environmental Research Accelerator (VERA) at the University of Vienna.

    The dating showed the fallout had only occurred in two time periods, 3.2 to 1.7 million years ago and eight million years ago. Current results from TU Munich are in line with these findings.

    A possible source of the supernovae is an ageing star cluster, which has since moved away from Earth, independent work led by TU Berlin has proposed in a parallel publication. The cluster has no large stars left, suggesting they have already exploded as supernovae, throwing out waves of debris.

    More information: Recent near-Earth supernovae probed by global deposition of interstellar radioactive 60Fe, Nature, DOI: 10.1038/nature17196

    The science team:

    A. Wallner, J. Feige, N. Kinoshita, M. Paul, L. K. Fifield, R. Golser, M. Honda, U. Linnemann, H. Matsuzaki, S. Merchel, G. Rugel, S. G. Tims, P. Steier, T. Yamagata & S. R. Winkler

    Affiliations

    Department of Nuclear Physics, Research School of Physics and Engineering, The Australian National University (ANU), Canberra, Australian Capital Territory 2601, Australia
    A. Wallner, L. K. Fifield & S. G. Tims
    University of Vienna, Faculty of Physics—Isotope Research, VERA Laboratory, Währinger Straße 17, 1090 Vienna, Austria
    J. Feige, R. Golser, P. Steier & S. R. Winkler
    Institute of Technology, Shimizu Corporation, Tokyo 135-8530, Japan
    N. Kinoshita
    Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
    M. Paul
    Graduate School of Pure and Applied Sciences, University of Tsukuba, Ibaraki 305-8577, Japan
    M. Honda
    Senckenberg Collections of Natural History Dresden, GeoPlasmaLab, Königsbrücker Landstraße 159, Dresden 01109, Germany
    U. Linnemann
    MALT (Micro Analysis Laboratory, Tandem accelerator), The University Museum, The University of Tokyo, Tokyo 113-0032, Japan
    H. Matsuzaki
    Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Helmholtz Institute for Resource Technology, 01328 Dresden, Germany
    S. Merchel & G. Rugel
    Graduate School of Integrated Basic Sciences, Nihon University, Tokyo 156-8550, Japan
    T. Yamagata

    Contributions

    A.W. initiated the study and wrote the main paper together with J.F., M.P. and L.K.F.; all authors were involved in the project and commented on the paper. A.W., with J.F., L.K.F. and S.R.W., organized the Eltanin sediment samples. N.K. and M.P. organized the crust samples. S.M. and U.L. organized the nodules. J.F. and S.M. were primarily responsible for sample preparation of the sediment and nodules and N.K. was responsible for the crusts. A.W., L.K.F. and S.G.T. performed the AMS measurements for 60Fe at the ANU. P.S., S.R.W., J.F. and A.W. performed the 26Al and 10Be measurements at VERA. G.R., S.M. and J.F. performed 10Be measurements at HZDR. N.K., M.H., H.M. and T.Y. performed 10Be measurements at MALT. J.F., A.W. and N.K. performed the data analysis.

    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 11:04 am on November 18, 2015 Permalink | Reply
    Tags: , , , Supernovas   

    From New Scientist: “Local supernova 2 million years ago solves cosmic ray puzzle” 

    NewScientist

    New Scientist

    17 November 2015
    Anna Nowogrodzki

    1
    NASA/CXC/SAO/Science Photo Library

    All signs point to a supernova. A stellar explosion 2 million years ago that flooded our neighbourhood with charged particles could be the answer to several cosmic puzzles.

    For years, astrophysicists have struggled to explain why there are so many high-energy cosmic rays – speeding charged particles that hit Earth from all directions. We’d expect most to have fled the galaxy long before reaching us, yet we see a lot of protons, as well as the antiprotons and positrons they produce in collisions.

    Researchers have previously proposed pulsars and dark matter to explain this oddity, but neither provides a complete solution: pulsars can’t explain the antiprotons, and dark matter can’t explain the antiprotons or positrons.

    A supernova could act as a local cosmic particle accelerator, but previous models haven’t been able to fully account for the number of cosmic rays.

    That might be because the distribution of these rays is uneven throughout the galaxy, says Dmitri Semikoz at the Astroparticle and Cosmology Laboratory in Paris. It’s like watching a firework display and assuming that the sky looks bright and colourful everywhere, instead of looking to see if someone recently set off fireworks nearby.

    Semikoz and his colleagues modelled a nearby supernova and predicted the cosmic ray energies we should see on Earth between 5000 and 10 million years later. Then they checked these against data from several current experiments.

    Ancient explosion

    The best fit was a single supernova exploding between 2 and 4 million years ago.

    And we already know about a supernova that fits this description. Parts of the deep ocean crust are thought to contain an isotope of iron that is the fingerprint of a 2-million-year-old supernova. The team suggests that this supernova could be the source of the cosmic rays.

    “The exciting thing is that in the end, the different things fit together,” says Michael Kachelriess of the Norwegian University of Science and Technology in Trondheim. “This was far from obvious when we started.”

    The team’s model generates several other predictions about the positrons we should see, so the next step will be to test those by gathering more data, says Kachelriess.

    “The evidence is already very tantalising,” says Francis Halzen, an astrophysicist at the University of Wisconsin-Madison. “Usually cosmic ray physics is one puzzle and one explanation. This is one explanation for many puzzles.”

    Journal reference: Physical Review Letters, DOI: 10.1103/PhysRevLett.115.181103

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  • richardmitnick 12:16 pm on November 16, 2015 Permalink | Reply
    Tags: , , , Supernovas   

    From NRAO: “35 Years of Constraints on Thermonuclear Supernova Progenitors with the VLA” 

    NRAO Icon
    National Radio Astronomy Observatory

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    11.16.2015
    Laura Chomiuk, Alicia M. Soderberg, Roger A. Chevalier, Seth Bruzewski, Ryan J. Foley, Jerod Parrent, Jay Strader, Carles Badenes, Claes Fransson, Atish Kamble, Raffaella Margutti, Michael P. Rupen, & Joshua D. Simon

    Today, the progenitors of Type Ia Supernovae (SNe) and their lower-luminosity thermonuclear cousins remain shrouded in mystery. While researchers agree that these SNe mark the explosions of white dwarf stars, it is unclear what destabilizes the white dwarf: merger with another white dwarf, accretion from a H-rich main sequence or giant star, or perhaps interaction with a helium star? Deep radio observations with the VLA can tackle this puzzle by searching for material in the environments of SNe, left over from the process of mass transfer onto the white dwarf.

    1

    When a SN shock interacts with surrounding material, relativistic electrons are accelerated and magnetic fields are amplified, yielding synchrotron emission. Therefore, radio observations of SNe provide insight into pre-SN mass loss and SN progenitors. In a paper recently submitted to Astrophysical Journal, our team combined archival radio observations from 30 years of legacy VLA operations with new observations from the Karl G. Jansky VLA. This yields a sample of 85 thermonuclear SNe observed by the VLA in the first year following explosion. None are detected. These radio limits imply that Type Ia supernovae explode in low-density environments.

    We use our limits on the density of material surrounding these SNe to constrain the fraction of thermonuclear SNe that might have red giant companions. We make use of legacy VLA observations of Galactic symbiotic binaries carried out by E. Seaquist and collaborators to characterize the density of material around white dwarfs with red giant companions, and find that, for many SNe, we can rule out such symbiotic progenitors. We conclude that ≲10% of thermonuclear SNe have red giant companions.

    Future work with the VLA can improve upon these results via: (a) further observations of Galactic symbiotic binaries that more completely pin down their wind properties; (b) additional observations of a large number of Type Ia SNe, providing even stronger constraints on the fraction with red giant companion; and (c) analysis of radio observations at longer times after explosion (1-100 years, as the SN transitions to a SN remnant) to probe the SN environment at larger radii.

    See the full article here .

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    The NRAO operates a complementary, state-of-the-art suite of radio telescope facilities for use by the scientific community, regardless of institutional or national affiliation: the Very Large Array (VLA), the Robert C. Byrd Green Bank Telescope (GBT), and the Very Long Baseline Array (VLBA)*.

    ALMA Array

    NRAO ALMA

    NRAO GBT
    NRAO GBT

    NRAO VLA
    NRAO VLA

    The NRAO is building two new major research facilities in partnership with the international community that will soon open new scientific frontiers: the Atacama Large Millimeter/submillimeter Array (ALMA), and the Expanded Very Large Array (EVLA). Access to ALMA observing time by the North American astronomical community will be through the North American ALMA Science Center (NAASC).
    *The Very Long Baseline Array (VLBA) comprises ten radio telescopes spanning 5,351 miles. It’s the world’s largest, sharpest, dedicated telescope array. With an eye this sharp, you could be in Los Angeles and clearly read a street sign in New York City!

    Astronomers use the continent-sized VLBA to zoom in on objects that shine brightly in radio waves, long-wavelength light that’s well below infrared on the spectrum. They observe blazars, quasars, black holes, and stars in every stage of the stellar life cycle. They plot pulsars, exoplanets, and masers, and track asteroids and planets.

     
  • richardmitnick 9:37 am on November 6, 2015 Permalink | Reply
    Tags: , , , Supernovas   

    From LBL- “Supernova Twins: Making Standard Candles More Standard Than Ever” 

    Berkeley Logo

    Berkeley Lab

    November 5, 2015
    Paul Preuss 415-272-3253

    Less than 20 years ago the world learned that the universe is expanding ever faster, propelled by dark energy. The discovery was made possible by Type Ia supernovae; extraordinarily bright and remarkably similar in brightness, they serve as standard candles essential for probing the universe’s history.

    In fact, Type Ia supernovae are far from standard. Intervening dust can redden and dim them, and the physics of their thermonuclear explosions differs — a single white dwarf (an Earth-sized star as massive as our sun) may explode after borrowing mass from a companion star, or two orbiting white dwarfs may collide and explode. These “normal” Type Ia’s can vary in brightness by as much as 40 percent. Brightness dispersion can be reduced by well-proven methods, but cosmology continues to be done with catalogues of supernovae that may differ in brightness by as much as 15 percent.

    Now members of the international Nearby Supernova Factory (SNfactory), based at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), have dramatically reduced the scatter in supernova brightnesses. Using a sample of almost 50 nearby supernovae, they identified supernova twins — pairs whose spectra are closely matched — which reduced their brightness dispersion to a mere eight percent. The distance to these supernovae can be measured about twice as accurately as before.

    The SNfactory results are reported in Improving cosmological distance measurements using twin Type Ia supernovae, accepted for publication by the Astrophysical Journal (ApJ) and available online at arxiv.org/abs/1511.01102.

    1
    From left, Greg Aldering, Kyle Boone, Hannah Fakhouri and Saul Perlmutter of the Nearby Supernova Factory. Behind them is a poster of a supernova spectrum. Matching spectra among different supernovae can double the accuracy of distance measurements. (Photo by Roy Kaltschmidt/Berkeley Lab)

    Comparing apples to apples

    “Instead of concentrating on what’s causing the differences among supernovae, the supernova-twins approach is to look at the spectra and seek the best matches, so as to compare like with like,” says Greg Aldering, the Berkeley Lab cosmologist who leads the SNfactory. “The assumption we tested is that if two supernovae look the same, they probably are the same.”

    Hannah Fakhouri, the lead author of the ApJ paper, initiated the twin study for her doctoral thesis. She says that the theoretical advantages of a twins match-up had long been discussed at Berkeley Lab; for the researchers who founded the SNfactory, including her thesis advisor, Nobel laureate Saul Perlmutter, one of the main goals was gathering a dataset of sufficient quality to test hypotheses like supernova twinning.

    Fakhouri’s timing was good; she was able to take advantage of precise spectrophotometry — simultaneous measures of spectra and brightness — of numerous nearby Type Ia’s, collected using the SNfactory’s SuperNova Integral Field Spectrograph (SNIFS) on the University of Hawaii’s 2.2-meter telescope on Mauna Kea.

    U Hawaii 2.2 meter telescope
    U Hawaii 2.2 meter telescope interior
    U Hawaii’s 2.2-meter telescope

    “Nearby” is relative; some SNfactory supernovae are more than a billion light years away. But all yield more comprehensive and detailed measurements than the really distant supernovae also needed for cosmology. The twin study used data from the first years of the SNfactory’s observations; further work will use hundreds of high-quality Type Ia spectra from the SNfactory, so far the only large database in the world that can be used for this work.

    Despite the surprising results, Fakhouri describes the initial research as “a long slog,” requiring hard work and attention to detail. One challenge was making fair comparisons of time series, in which spectra are taken at frequent intervals as a supernova reaches maximum luminosity, then slowly fades; different colors (wavelengths) brighten and fade at different rates.

    Because of demands on telescope time and other issues like weather, the time series of different supernovae can’t be sampled uniformly. SNfactory member Rollin Thomas, of Berkeley Lab’s Computational Cosmology Center, recommended a mathematical procedure called Gaussian Process regression to fill the gaps. Fakhouri says the outcome “was a big breakthrough.”

    Cleaning up the spectra and ranking the supernovae for twinness was done completely “blind” — the researchers had no information about the supernovae except their spectra. “The unblinding process was suspenseful,” Fakhouri says. “We might have found that twinning was completely useless.” The result was a relief: the closer the twins’ spectra, the closer their brightnesses.

    The result strongly suggests that the long-accepted 15-percent uncertainty in Type Ia brightness is not merely statistical; it masks real but unknown differences in the nature of the supernovae themselves. The twin method’s dramatic reduction of brightness dispersion suggests that hidden unknowns about the physical explosion processes of twins have been severely reduced as well, a strong step toward using such supernovae as true standard candles.

    The best of the bunch

    When Fakhouri received her doctorate, graduate student Kyle Boone, second author of the ApJ paper, took over the final steps of the analysis. “I started by comparing the twin method to other methods for reducing dispersion in brightness.”

    The conventional approach has been to fit a curve through a series of data points of brightness versus time: a lightcurve. Dimmer Type Ia’s have narrower lightcurves and are redder; this fact is used to “standardize” supernovae, that is, to adjust their brightnesses to a common system.

    The twin method, says Boone, “beats the lightcurve method without even trying. Plus, we found this can be done with just one spectrum — an entire lightcurve is not needed.”

    Other recent methods are more subtle and detailed, but all have drawbacks compared to twinning. “The main competing technique gives excellent results but depends on wavelengths in the near infrared, where dispersion of the starting brightness is much less,” Boone says. “That will be difficult to use with distant supernovae, whose high redshift makes near-infrared wavelengths inaccessible.”

    Fakhouri says, “Supernovae offer unique advantages for cosmology, but we need multiple techniques,” including statistical methods charting how dark energy has shaped the structure of the universe. “The great thing about nature is that it provides different kinds of probes that can be decoupled from one another.”

    Supernovae are a singular asset, notes Aldering: “Supernovae found dark energy, and they still provide the strongest constraints on dark energy properties.”

    Says Boone, “We are working to see how well the twins technology can be applied to a very large sample of well-characterized, high-redshift supernovae that a space telescope like WFIRST could provide.” NASA plans to launch WFIRST, the Wide-Field Infrared Survey Telescope, in the mid-2020s. Among other investigations, it will capture the spectra of many thousands of distant Type Ia supernovae.

    When based on a reference sample of well-measured supernovae large enough for every new supernova to find its perfect twin, twin-supernova technology could lead to precise measures of dark energy’s effect on the universe over the past 10 billion years. Each point in space and time so labeled will be an accurate milestone on the journey that led to the universe we live in today.

    This work was supported by DOE’s Office of Science and by the National Center for Scientific Research/National Institute of Nuclear and Particle Physics (CNRS/IN2P3), the CNRS National Institute for Earth Sciences and Astronomy (CNRS/INSU), and the Laboratory of Nuclear and High-Energy Physics (LPNHE) in France; support in Germany was provided by the German Research Foundation (DFG) and in China by Tsinghua University. The researchers acknowledge the assistance of the Palomar Observatory, the High Performance Wireless Research and Education Network (HPWREN), the University of Hawaii 2.2-meter telescope, and DOE’s National Energy Research Scientific Computing Center (NERSC) for storage and computing time.

    See the full article here .

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