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  • richardmitnick 2:09 pm on August 25, 2015 Permalink | Reply
    Tags: , Supernovas,   

    From Symmetry: “All about supernovae” 

    Symmetry

    1
    Twenty years ago, astronomers witnessed one of the brightest stellar explosions in more than 400 years. The titanic supernova, called SN 1987A, blazed with the power of 100 million suns for several months following its discovery on Feb. 23, 1987. Observations of SN 1987A, made over the past 20 years by NASA’s Hubble Space Telescope and many other major ground- and space-based telescopes, have significantly changed astronomers’ views of how massive stars end their lives. Astronomers credit Hubble’s sharp vision with yielding important clues about the massive star’s demise.

    This Hubble telescope image shows the supernova’s triple-ring system, including the bright spots along the inner ring of gas surrounding the exploded star. A shock wave of material unleashed by the stellar blast is slamming into regions along the inner ring, heating them up, and causing them to glow. The ring, about a light-year across, was probably shed by the star about 20,000 years before it exploded.
    Date Released: 22 February 2007
    Source http://hubblesite.org/newscenter/archive/releases/2007/10/image/a/
    Author NASA, ESA, P. Challis, and R. Kirshner (Harvard-Smithsonian Center for Astrophysics)

    NASA Hubble Telescope
    NASA/ESA Hubble

    Somewhere in the cosmos, a star is reaching the end of its life.

    Maybe it’s a massive star, collapsing under its own gravity. Or maybe it’s a dense cinder of a star, greedily stealing matter from a companion star until it can’t handle its own mass.

    Whatever the reason, this star doesn’t fade quietly into the dark fabric of space and time. It goes kicking and screaming, exploding its stellar guts across the universe, leaving us with unparalleled brightness and a tsunami of particles and elements. It becomes a supernova. Here are ten facts about supernovae that will blow your mind.

    1. The oldest recorded supernova dates back almost 2000 years

    In 185 AD, Chinese astronomers noticed a bright light in the sky. Documenting their observations in the Book of Later Han, these ancient astronomers noted that it sparkled like a star, appeared to be half the size of a bamboo mat and did not travel through the sky like a comet. Over the next eight months this celestial visitor slowly faded from sight. They called it a “guest star.”

    Two millennia later, in the 1960s, scientists found hints of this mysterious visitor in the remnants of a supernova approximately 8000 light-years away. The supernova, SN 185, is the oldest known supernova recorded by humankind.

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    Combined X-ray image from Chandra and XMM-Newton of RCW 86. Low energy X-rays are in red, medium energies in green, and high energies in blue. RCW 86 is the probable remnant of SN 185.

    ESA XMM Newton
    ESA/XMM-Newton

    NASA Chandra Telescope
    NASA/Chandra

    2
    2. Many of the elements we’re made of come from supernovae [This is incorrect. Absolutely everything we are made of was released in a supernova.]

    Everything from the oxygen you’re breathing to the calcium in your bones, the iron in your blood and the silicon in your computer was brewed up in the heart of a star.

    As a supernova explodes, it unleashes a hurricane of nuclear reactions. These nuclear reactions produce many of the building blocks of the world around us. The lion’s share of elements between oxygen and iron comes from core-collapse supernovae, those massive stars that collapse under their own gravity. They share the responsibility of producing the universe’s iron with thermonuclear supernovae, white dwarves that steal mass from their binary companions. Scientists also believe supernovae are a key site for the production of most of the elements heavier than iron.

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    Two men in a rubber raft inspect the wall of photodetectors of the partly filled Super-Kamiokande neutrino detector.

    3. Supernovae are neutrino factories

    In a 10-second period, a core-collapse supernova will release a burst of more than 1058 neutrinos, ghostly particles that can travel undisturbed through almost everything in the universe.

    Outside of the core of a supernova, it would take a light-year of lead to stop a neutrino. But when a star explodes, the center can become so dense that even neutrinos take a little while to escape. When they do escape, neutrinos carry away 99 percent of the energy of the supernova.

    Scientists watch for that burst of neutrinos using an early warning system called SNEWS. SNEWS is a network of neutrino detectors across the world. Each detector is programmed to send a datagram to a central computer whenever it sees a burst of neutrinos. If more than two experiments observe a burst within 10 seconds, the computer issues an automatic alert to the astronomical community to look out for an exploding star.

    But you don’t have to be an expert astronomer to receive an alert. Anyone can sign up to be among the first to know that a star’s core has collapsed.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    4. Supernovae are powerful particle accelerators

    Supernovae are natural space laboratories; they can accelerate particles to at least 1000 times the energy of particles in the Large Hadron Collider, the most powerful collider on Earth.

    The interaction between the blast of a supernova and the surrounding interstellar gas creates a magnetized region, called a shock. As particles move into the shock, they bounce around the magnetic field and get accelerated, much like a basketball being dribbled closer and closer to the ground. When they are released into space, some of these high-energy particles, called cosmic rays, eventually slam into our atmosphere, colliding with atoms and creating showers of secondary particles that rain down on our heads.

    5. Supernovae produce radioactivity

    In addition to forging elements and neutrinos, the nuclear reactions inside of supernovae also cook up radioactive isotopes. Some of this radioactivity emits light signals, such as gamma rays, that we can see in space.

    This radioactivity is part of what makes supernovae so bright. It also provides us with a way to determine if any supernovae have blown up near Earth. If a supernova occurred close enough to our planet, we’d be sprayed with some of these unstable nuclei. So when scientists come across layers of sediment with spikes of radioactive isotopes, they know to investigate whether what they’ve found was spit out by an exploding star.

    In 1998, physicists analyzed crusts from the bottom of the ocean and found layers with a surge of 60Fe, a rare radioactive isotope of iron that can be created in copious amounts inside supernovae. Using the rate at which 60Fe decays over time, they were able to calculate how long ago it landed on Earth. They determined that it was most likely dumped on our planet by a nearby supernova about 2.8 million years ago.

    6. A nearby supernova could cause a mass extinction

    If a supernova occurred close enough, it could be pretty bad news for our planet. Although we’re still not sure about all the ways being in the midst of an exploding star would affect us, we do know that supernovae emit truckloads of high-energy photons such as X-rays and gamma rays. The incoming radiation would strip our atmosphere of its ozone. All of the critters in our food chain from the bottom up would fry in the sun’s ultraviolet rays until there was nothing left on our planet but dirt and bones.

    Statistically speaking, a supernova in our own galaxy has been a long time coming.

    Supernovae occur in our galaxy at a rate of about one or two per century. Yet we haven’t seen a supernova in the Milky Way in around 400 years. The most recent nearby supernova was observed in 1987, and it wasn’t even in our galaxy. It was in a nearby satellite galaxy called the Large Magellanic Cloud [LMC].

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    LMC

    But death by supernova probably isn’t something you have to worry about in your lifetime, or your children’s or grandchildren’s or great-great-great-grandchildren’s lifetime. IK Pegasi, the closest candidate we have for a supernova, is 150 light-years away—too far to do any real damage to Earth.

    Even that 2.8-million-year-old supernova that ejected its radioactive insides into our oceans was at least 100 light-years from Earth, which was not close enough to cause a mass-extinction. The physicists deemed it a “near miss.”

    7. Supernovae light can echo through time

    Just as your voice echoes when its sound waves bounce off a surface and come back again, a supernova echoes in space when its light waves bounce off cosmic dust clouds and redirect themselves toward Earth.

    Because the echoed light takes a scenic route to our planet, this phenomenon opens a portal to the past, allowing scientists to look at and decode supernovae that occurred hundreds of years ago. A recent example of this is SN1572, or Tycho’s supernova, a supernova that occurred in 1572. This supernova shined brighter than Venus, was visible in daylight and took two years to dim from the sky.

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    Remnant of SN 1572 as seen in X-ray light from the Chandra X-ray Observatory

    In 2008, astronomers found light waves originating from the cosmic demolition site of the original star. They determined that they were seeing light echoes from Tycho’s supernova. Although the light was 20 billion times fainter than what astronomer Tycho Brahe observed in 1572, scientists were able to analyze its spectrum and classify the supernova as a thermonuclear supernova.

    More than four centuries after its explosion, light from this historical supernova is still arriving at Earth.

    5

    8. Supernovae were used to discover dark energy

    Because thermonuclear supernovae are so bright, and because their light brightens and dims in a predictable way, they can be used as lighthouses for cosmology.

    In 1998, scientists thought that cosmic expansion, initiated by the big bang, was likely slowing down over time. But supernova studies suggested that the expansion of the universe was actually speeding up.

    8
    According to the Big Bang model, the universe expanded from an extremely dense and hot state and continues to expand today.

    Scientists can measure the true brightness of supernovae by looking at the timescale over which they brighten and fade. By comparing how bright these supernovae appear with how bright they actually are, scientists are able to determine how far away they are.

    Scientists can also measure the increase in the wavelength of a supernova’s light as it moves farther and farther away from us. This is called the redshift.

    Comparing the redshift with the distances of supernovae allowed scientists to infer how the rate of expansion has changed over the history of the universe. Scientists believe that the culprit for this cosmic acceleration is something called dark energy.

    9. Supernovae occur at a rate of approximately 10 per second

    By the time you reach the end of this sentence, it is likely a star will have exploded somewhere in the universe.

    As scientists evolve better techniques to explore space, the number of supernovae they discover increases. Currently they find over a thousand supernovae per year.

    But when you look deep into the night sky at bright lights shining from billions of light-years away, you’re actually looking into the past. The supernovae that scientists are detecting stretch back to the very beginning of the universe. By adding up all of the supernovae they’ve observed, scientists can figure out the rate at which supernovae occur across the entire universe.

    Scientists estimate about 10 supernovae occur per second, exploding in space like popcorn in the microwave.

    10. We’re about to get much better at detecting far-away supernovae

    Even though we’ve been aware of these exploding stars for millennia, there’s still so much we don’t know about them. There are two known types of supernovae, but there are many different varieties that scientists are still learning about.

    Supernovae could result from the merger of two white dwarfs. Alternatively, the rotation of a star could create a black hole that accretes material and launches a jet through the star. Or the density of a star’s core could be so high that it starts creating electron-positron pairs, causing a chain reaction in the star.

    Right now, scientists are mapping the night sky with the Dark Energy Survey, or DES. Scientists can discover new supernova explosions by looking for changes in the images they take over time.

    Dark Energy Survey
    DECam
    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    DES, the DeCam built at FNAL, and the CTIO Victor M Blanco Telescope in Chile in which DECam is housed

    Another survey currently going on is the All-Sky Automated Survey for Supernovae, or the ASAS-SN, which recently observed the most luminous supernova ever discovered.

    All Sky Automated Survey for Supernovas
    ASAS-SN telescope

    In 2019, the Large Synoptic Survey Telescope, or LSST, will revolutionize our understanding of supernovae. LSST is designed to collect more light and peer deeper into space than ever before. It will move rapidly across the sky and take more images in larger chunks than previous surveys. This will increase the number of supernovae we see by hundreds of thousands per year.

    LSST Exterior
    LSST Telescope
    LSST Camera
    LSST home and telescope to be biuilt in Chile

    Studying these astral bombs will expand our knowledge of space and bring us even closer to understanding not just our origin, but the cosmic reach of the universe.

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 10:10 am on August 4, 2015 Permalink | Reply
    Tags: , , , Supernovas   

    From SPACE.com: “3D Supernova Simulation Turns Back Clock on Star Explosions” 

    space-dot-com logo

    SPACE.com

    August 03, 2015
    Sarah Lewin

    1
    This visualization depicts a massive star about to collapse and explode into a supernova. Researchers found in the new simulation that the wrinkles that develop just before collapse are crucial to detonation. Credit: S. M. Couch

    Enormous stars collapse in ultramassive supernova explosions — now in 3D! For the first time ever, researchers have turned back the clock on a star’s final moments to simulate how wrinkles in its violent collapse trigger a vast explosion.

    As massive stars age, they build up more and more iron in their cores, which cannot be used by the star as fuel. Eventually, when the core gets big enough, it collapses and, sometimes, incites a huge explosion. Most simulations start with a star already on the brink of collapse, with the different layers inside the star in perfect concentric rings. But models with those simplified starting conditions stubbornly refuse to blow.

    “Almost all supernova simulations follow about 1 second of physical time,” said Sean Couch, a physicist and astronomer at Michigan State University and lead author of the new paper. “What we did that was different is, we wound the clock back 3 minutes. That’s really challenging; it’s never been done before. We then show this has an important and big impact on the likelihood for successful supernova explosions.”

    Such a feat was very technologically demanding, but it proved necessary because models starting right at the collapse just wouldn’t explode in a supernova, Couch said. Instead, the shock would peter out, and the collapsing star would become a black hole.

    “It’s the difference between an onion” — the old, simplified starting point — “and cabbage,” Couch told Space.com. “You slice cabbage, and there’s wrinkles on the inside. It’s still basically a sphere, but it’s not nearly as concentrically layered as the onion will be.”

    Those extra few moments, where the “onion” model had the chance to wrinkle into a “cabbage” more like a complex, real star before collapsing, seem to cause enough turbulence to push the system over the edge into a supernova.

    Just modeling those extra 3 minutes back in time was a huge technological challenge, Couch said — the simulation on the supercomputer took about one month to complete, and they could run it only once. Therefore, the researchers chose their star carefully: one about 12 million years old, and 15 times the mass of the sun, that they thought would likely go supernova.

    To extend their research, the scientists are modeling four types of stars they think might lead to supernovas, and they’re hoping to push the simulation even further back in time. Couch said it might be possible to understand and model the forces within a star, to go as far as an hour before the collapse. (“An epic challenge,” Couch called it.)

    The difficulty with modeling stars is the difference in timescales, Couch said — a star evolves over the course of millions of years, but the supernova mechanism is on a millisecond scale. Incredible levels of precision and complexity are needed to understand that millisecond.

    “We know that we’ve been working with unrealistic initial conditions; it’s just only come to light in the last couple of years that it matters,” Couch said. “What we’re learning now is that the details of these stars matter.”

    The research was detailed in the July 21 edition of The Astrophysical Journal.

    See the full article here.

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  • richardmitnick 12:55 pm on June 4, 2015 Permalink | Reply
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    From UC Berkeley: “Exiled stars explode far from home” 

    UC Berkeley

    UC Berkeley

    June 4, 2015
    Robert Sanders, Media Relations

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    Animated GIF contrasting the supernova as seen in 2009 by the CFHT and the sharper image obtained in 2013 by the Hubble Space Telescope. (Image by Melissa Graham, CFHT and HST)

    Sharp images obtained by the Hubble Space Telescope confirm that three supernovae discovered several years ago exploded in the dark emptiness of intergalactic space, having been flung from their home galaxies millions or billions of years earlier.

    NASA Hubble Telescope
    NASA/ESA Hubble

    Most supernovae are found inside galaxies containing hundreds of billions of stars, one of which might explode per century per galaxy.

    These lonely supernovae, however, were found between galaxies in three large clusters of several thousand galaxies each. The stars’ nearest neighbors were probably 300 light years away, nearly 100 times farther than our sun’s nearest stellar neighbor, Proxima Centauri, 4.24 light years distant.

    Such rare solitary supernovae provide an important clue to what exists in the vast empty spaces between galaxies, and can help astronomers understand how galaxy clusters formed and evolved throughout the history of the universe.

    The solitary worlds reminded study leader Melissa Graham, a University of California, Berkeley, postdoctoral fellow and avid sci-fi fan, of the fictional star Thrial, which, in the Iain Banks novel Against a Dark Background, lies a million light years from any other star. One of its inhabited planets, Golter, has a nearly starless night sky.

    Any planets around these intracluster stars – all old and compact stars that exploded in what are called Type Ia supernovae – were no doubt obliterated by the explosions, but they, like Golter, would have had a night sky depleted of bright stars, Graham said. The density of intracluster stars is about one-millionth what we see from Earth.

    “It would have been a fairly dark background indeed,” she said, “populated only by the occasional faint and fuzzy blobs of the nearest and brightest cluster galaxies.”

    Graham and her colleagues – David Sand of Texas Tech University in Lubbock, Dennis Zaritsky of the University of Arizona in Tucson and Chris Pritchet of the University of Victoria in British Columbia – will report their analysis of the three stars in a paper to be presented Friday, June 5, at a conference on supernovae at North Carolina State University in Raleigh. Their paper has also been accepted by the Astrophysical Journal.

    Clusters of thousands of galaxies

    The new study confirms the discovery between 2008 and 2010 of three apparently hostless supernovae by the Multi-Epoch Nearby Cluster Survey using the Canada-France-Hawaii Telescope [CFHT} on Mauna Kea in Hawaii.

    Canada-France-Hawaii Telescope
    Canada France Hawaii Telescope Interior
    CFHT

    The CFHT was unable to rule out a faint galaxy hosting these supernovae. But the sensitivity and resolution of images from the Hubble Space Telescope’s Advanced Camera for Surveys [ACS] are 10 times better and clearly show that the supernovae exploded in empty space, far from any galaxy. They thus belong to a population of solitary stars that exist in most if not all clusters of galaxies, Graham said

    NASA Hubble ACS
    ACS

    While stars and supernovae typically reside in galaxies, galaxies situated in massive clusters experience gravitational forces that wrench away about 15 percent of the stars, according to a recent survey. The clusters have so much mass, though, that the displaced stars remain gravitationally bound within the sparsely populated intracluster regions.

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    One of the four supernovae (top, 2009) may be part of a dwarf galaxy or globular cluster visible on the 2013 HST image (bottom). (Image by Melissa Graham, CFHT and HST)

    Once dispersed, these lonely stars are too faint to be seen individually unless they explode as supernovae. Graham and her colleagues are searching for bright supernovae in intracluster space as tracers to determine the population of unseen stars. Such information provides clues about the formation and evolution of large scale structures in the universe.

    “We have provided the best evidence yet that intracluster stars truly do explode as Type Ia supernovae,” Graham said, “and confirmed that hostless supernovae can be used to trace the population of intracluster stars, which is important for extending this technique to more distant clusters.”

    Graham and her colleagues also found that a fourth exploding star discovered by CFHT appears to be inside a red, round region that could be a small galaxy or a globular cluster. If the supernova is in fact part of a globular cluster, it marks the first time a supernova has been confirmed to explode inside these small, dense clusters of fewer than a million stars. All four supernovae were in galaxy clusters sitting about a billion light years from Earth.

    “Since there are far fewer stars in globular clusters, only a small fraction of the supernovae are expected to occur in globular clusters,” Graham said. “This might be the first confirmed case, and may indicate that the fraction of stars that explode as supernovae is higher in either low-mass galaxies or globular clusters.”

    Graham said that most theoretical models for Type Ia supernovae involve a binary star system, so the exploding stars would have had a companion throughout their lifetimes.

    “This is no love story, though,” she added. “The companion was either a lower-mass white dwarf that eventually got too close and was tragically fragmented into a ring that was cannibalized by the primary star, or a regular star from which the primary white dwarf star stole sips of gas from its outer layers. Either way, this transfer of material caused the primary to become unstably massive and explode as a Type Ia supernova.”

    Graham’s postdoctoral fellowship is supported by gifts from Gary and Cynthia Bengier.

    See the full article here.

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  • richardmitnick 9:22 pm on May 22, 2015 Permalink | Reply
    Tags: , , , Supernovas   

    From New Scientist: “Supernova space bullets could have seeded Earth’s iron core” 

    NewScientist

    New Scientist

    20 May 2015
    Jacob Aron

    1
    Shooting stars (Image: X-ray: NASA/CXC/SAO; Infrared: NASA/JPL-Caltech; Optical: MPIA, Calar Alto, O. Krause et al)

    Supernova shoot-em-ups could be responsible for Earth’s iron core. An analysis suggests that certain stars fire off massive iron bullets when they die.

    Stars fuse the hydrogen and helium present in the early universe into heavier elements, like iron. When stars reach the end of their lives, they explode in supernovae, littering these elements throughout space where they can eventually form planets.

    A particular kind of supernova called a type Ia, the result of the explosion of a dense stellar corpse called a white dwarf star, seems to be responsible for most of the iron on Earth.

    These stars also play an important role in our understanding of distance in the universe. That’s because the white dwarfs only blow up when they reach a certain, fixed mass, so we can use the light of these explosions as a “standard candle” to tell how far away they are.

    But astronomers still haven’t figured out exactly what causes white dwarfs to hit this critical limit.

    “Most of our iron on Earth comes from supernovae of this kind,” says Noam Soker of the Technion Israel Institute of Technology in Haifa. “It is embarrassing that we still don’t know what brings these white dwarfs to explode.”

    Lumpy stars

    When a star goes supernova, it leaves behind a cloud of ejected material called a supernova remnant. This remnant should be spherical – but some have extra bumps that could offer a clue to the supernova’s origin.

    Now Soker and his colleague Danny Tsebrenko say that massive clumps of iron produced within a white dwarf in the process of going supernova could be punching through the remnant like bullets, creating these bumps. The iron bullets aren’t solid chunks of metal, but a more diffuse cloud of molecules.

    Some supernova remnants have two bumps on opposite sides, which the researchers call “ears”.

    The iron bullets form along the rotation axis of an exploding white dwarf, firing out at either end, says Soker. A white dwarf can only be spinning fast enough to allow this if it is the result of two smaller dwarfs merging, he adds.

    The bullets could also shed light on our origins. Soker and Tsebrenko estimate that these clouds of iron would be several times the mass of Jupiter. They would spread and could eventually seed dust clouds with iron that would go on to form stars and planets, providing an origin for Earth’s core, says Soker.

    Reference: arxiv.org/abs/1505.02034v1

    See the full article here.

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  • richardmitnick 8:51 am on May 22, 2015 Permalink | Reply
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    From ANU: “Supernova ignition surprises scientists” 

    ANU Australian National University Bloc

    Australian National University

    21 May 2015
    No Writer Credit

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

    Gemini South telescope
    Gemini South Interior
    Gemini

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

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

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

    NASA Kepler Telescope
    NASA/Kepler

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

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

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

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

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

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

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

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

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

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

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

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

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

    The findings are published in Nature.

    See the full article here.

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

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

     
  • richardmitnick 3:58 pm on May 20, 2015 Permalink | Reply
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    From Carnegie: “Strong UV Pulse Reveals Supernova’s Origin Story” 

    Carnegie Institution for Science
    Carnegie Institution for Science

    May 20, 2015
    No Writer Credit

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

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

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

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

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

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

    NASA SWIFT Telescope
    NASA/Swift

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

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

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

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

    Apache Point Observatory
    Apache Point Observatory interior
    Apache Point Observatory

    Gemini North telescope
    Gemini North Interior
    Gemini Observatory

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

    Nordic Optical Telescope
    Nordic Opitcal Telescope Interior
    Nordic Optical Telescope

    Keck Observatory
    Keck Observatory Interior
    Keck Observatory

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

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

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

    See the full article here.

    Please help promote STEM in your local schools.

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    Carnegie Institution of Washington Bldg

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

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

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

    NASA SOFIA Banner

    SOFIA (Stratospheric Observatory For Infrared Astronomy)

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

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

    Nicholas Veronico

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

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

    Kate K. Squires

    Armstrong Flight Research Center, Edwards, Calif. 

    661-276-2020 

    kate.k.squires@nasa.gov

    1

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

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

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

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

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

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

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

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

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

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

    For more information about SOFIA, visit:

    http://www.nasa.gov/sofia

    or

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

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

    http://www.sofia.usra.edu

    or

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

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

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

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

    U Arizona bloc

    University of Arizona

    April 10, 2015
    Daniel Stolte

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

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

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

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

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

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

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

    U Arizona Mt Lemmon Sky Center
    Mt Lemmon

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

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

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

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

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

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

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

    NASA Hubble Telescope
    NASA/ESA Hubble

    NASA SWIFT Telescope
    NASA/Swift

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

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

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

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

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

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

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

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

    LSST Exterior
    LSST Interior
    LSST

    NOAO Super-LOTIS Telescope
    Super-LOTIS

    Contacts

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

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    U Arizona campus

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

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

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

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

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

    NASA SOFIA Banner

    SOFIA (Stratospheric Observatory For Infrared Astronomy)

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

    Nicholas Veronico

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

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

    Kate K. Squires

    Armstrong Flight Research Center, Edwards, Calif. 

    661-276-2020 

    kate.k.squires@nasa.gov

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

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

    ESA Herschel
    ESA/Herschel

    NRAO VLA
    NRAO/VLA

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

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

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

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

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

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

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

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

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

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

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

    For more information about SOFIA, visit:

    http://www.nasa.gov/sofia

    or

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

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

    http://www.sofia.usra.edu

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

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

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

    Nautilus

    Nautilus

    March 19, 2015
    Julia Rosen

    How a star explosion may have shaped life on Earth.

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

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

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

    ALMA Array
    ALMA

    NASA Hubble Telescope
    Hubble

    NASA Chandra Telescope

    Chandra

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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.

     
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