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  • richardmitnick 8:35 pm on August 4, 2021 Permalink | Reply
    Tags: "Stars Are Exploding in Dusty Galaxies. We Just Can’t Always See Them", , , , , , , Supernovae   

    From NASA JPL-Caltech (US) : “Stars Are Exploding in Dusty Galaxies. We Just Can’t Always See Them” 

    NASA JPL Banner

    From NASA JPL-Caltech (US)

    Aug 04, 2021
    News Media Contact

    Calla Cofield
    Jet Propulsion Laboratory, Pasadena, Calif.
    626-808-2469
    calla.e.cofield@jpl.nasa.gov

    by Adam Hadhazy

    1
    Hidden Supernova Spotted by NASA Spitzer Infared Space Telescope
    The image shows galaxy Arp 148, captured by NASA’s Spitzer and Hubble telescopes. Specially processed Spitzer data is shown inside the white circle, revealing infrared light from a supernova hidden by dust.
    Credit: National Aeronautics Space Agency (US)/JPL-Caltech (US).

    Inside the white circle is specially-processed Spitzer data, which reveals infrared light from a supernova that is hidden by dust. Supernovae are massive stars that have exploded after running out of fuel. They radiate most brightly in visible light (the kind the human eye can detect), but these wavelengths are obscured by dust. Infrared light, however, can pass through dust.

    The analysis of Arp 148 was part of an effort to find hidden supernovae in 40 dust-choked galaxies that also emit high levels of infrared light. These galaxies are known as luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs, respectively). The dust in LIRGs and ULIRGs absorbs optical light from objects like supernovae but allows infrared light from these same objects to pass through unobstructed for telescopes like Spitzer to detect.

    NASA’s Jet Propulsion Laboratory (US), Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology (US), also in Pasadena. Caltech manages JPL for NASA.

    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU). The Space Telescope Science Institute (US) conducts Hubble science operations. The institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc. (US), Washington, D.C.

    Exploding stars generate dramatic light shows. Infrared telescopes like Spitzer can see through the haze and to give a better idea of how often these explosions occur.

    You’d think that supernovae – the death throes of massive stars and among the brightest, most powerful explosions in the universe – would be hard to miss. Yet the number of these blasts observed in the distant parts of the universe falls way short of astrophysicists’ predictions.

    A new study [MNRAS] using data from NASA’s recently retired Spitzer Space Telescope reports the detection of five supernovae that, going undetected in optical light, had never been seen before. Spitzer saw the universe in infrared light, which pierces through dust clouds that block optical light – the kind of light our eyes see and that unobscured supernovae radiate most brightly.

    To search for hidden supernovae, the researchers looked at Spitzer observations of 40 dusty galaxies. (In space, dust refers to grain-like particles with a consistency similar to smoke.) Based on the number they found in these galaxies, the study confirms that supernovae do indeed occur as frequently as scientists expect them to. This expectation is based on scientists’ current understanding of how stars evolve. Studies like this are necessary to improve that understanding, by either reinforcing or challenging certain aspects of it.

    “These results with Spitzer show that the optical surveys we’ve long relied on for detecting supernovae miss up to half of the stellar explosions happening out there in the universe,” said Ori Fox, a scientist at the Space Telescope Science Institute in Baltimore, Maryland, and lead author of the new study, published in the Monthly Notices of the Royal Astronomical Society [above]. “It’s very good news that the number of supernovae we’re seeing with Spitzer is statistically consistent with theoretical predictions.”

    The “supernova discrepancy” – that is, the inconsistency between the number of predicted supernovae and the number observed by optical telescopes – is not an issue in the nearby universe. There, galaxies have slowed their pace of star formation and are generally less dusty. In the more distant reaches of the universe, though, galaxies appear younger, produce stars at higher rates, and tend to have higher amounts of dust. This dust absorbs and scatters optical and ultraviolet light, preventing it from reaching telescopes. So researchers have long reasoned that the missing supernovae must exist and are just unseen.

    “Because the local universe has calmed down a bit since its early years of star-making, we see the expected numbers of supernovae with typical optical searches,” said Fox. “The observed supernova-detection percentage goes down, however, as you get farther away and back to cosmic epochs where dustier galaxies dominated.”

    Detecting supernovae at these far distances can be challenging. To perform a search for supernovae shrouded within murkier galactic realms but at less extreme distances, Fox’s team selected a local set of 40 dust-choked galaxies, known as luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs, respectively). The dust in LIRGs and ULIRGs absorbs optical light from objects like supernovae but allows infrared light from these same objects to pass through unobstructed for telescopes like Spitzer to detect.

    The researchers’ hunch proved correct when the five never-before-seen supernovae came to (infrared) light. “It’s a testament to Spitzer’s discovery potential that the telescope was able to pick up the signal of hidden supernovae from these dusty galaxies,” said Fox.

    “It was especially fun for several of our undergraduate students to meaningfully contribute to this exciting research,” added study co-author Alex Filippenko, a professor of astronomy at the University of California- Berkeley (US). “They helped answer the question, ‘Where have all the supernovae gone?’”

    The types of supernovae detected by Spitzer are known as “core-collapse supernovae,” involving giant stars with at least eight times the mass of the Sun. As they grow old and their cores fill with iron, the big stars can no longer produce enough energy to withstand their own gravity, and their cores collapse, suddenly and catastrophically.

    The intense pressures and temperatures produced during the rapid cave-in forms new chemical elements via nuclear fusion. The collapsing stars ultimately rebound off their ultra-dense cores, blowing themselves to smithereens and scattering those elements throughout space. Supernovae produce “heavy” elements, such as most metals. Those elements are necessary for building up rocky planets, like Earth, as well as biological beings. Overall, supernova rates serve as an important check on models of star formation and the creation of heavy elements in the universe.

    “If you have a handle on how many stars are forming, then you can predict how many stars will explode,” said Fox. “Or, vice versa, if you have a handle on how many stars are exploding, you can predict how many stars are forming. Understanding that relationship is critical for many areas of study in astrophysics.”

    Next-generation telescopes, including NASA’s Nancy Grace Roman Space Telescope and the James Webb Space Telescope, will detect infrared light, like Spitzer.

    “Our study has shown that star formation models are more consistent with supernova rates than previously thought,” said Fox. “And by revealing these hidden supernovae, Spitzer has set the stage for new kinds of discoveries with the Webb and Roman space telescopes.”

    More About the Mission

    NASA’s Jet Propulsion Laboratory in Southern California conducted mission operations and managed the Spitzer Space Telescope mission for the agency’s Science Mission Directorate in Washington. Science operations were conducted at the Spitzer Science Center at Caltech in Pasadena. Spacecraft operations were based at Lockheed Martin Space (US) in Littleton, Colorado. Data are archived at the Infrared Science Archive housed at Caltech IPAC-Infrared Processing and Analysis Center (US). Caltech manages JPL for NASA.

    More information about Spitzer is available at:

    https://www.nasa.gov/mission_pages/spitzer/main

    See the full article here .


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    NASA JPL Campus

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

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  • richardmitnick 9:03 pm on July 15, 2021 Permalink | Reply
    Tags: "Exploding stars may have assaulted ancient Earth", 1999 The era of supernova geochemistry had begun [see PRL article link included]., ASM: accelerator mass spectrometer at TUM, , , , , Iron-60 forged in the cores of large stars-which has a half-life of 2.6 million years and is not made naturally on Earth., Kilonovae, , , Supernovae,   

    From Science Magazine: “Exploding stars may have assaulted ancient Earth” 

    From Science Magazine

    Jul. 15, 2021
    Daniel Clery

    1

    The Crab nebula is the remains of a supernova more than 6000 light-years away—too far to harm Earth.
    National Aeronautics Space Agency (US); European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU); J. Hester and A. Loll/Arizona State University (US).

    For our Australopithecus ancestors who roamed Africa 2.5 million years ago, the bright new star in the sky surely would have aroused curiosity. As luminous as the full Moon, it would have cast shadows at night and been visible during the day. As the supernova faded over the following months, it probably also faded from memory. But it left other traces, now coming to light.

    Over the past 2 decades, researchers have found hundreds of radioactive atoms, trapped in seafloor minerals, that came from an ancient explosion marking the death of a nearby star. Its fusion fuel exhausted, the star had collapsed, generating a shock wave that blasted away its outer layers in an expanding ball of gas and dust so hot that it briefly glowed as bright as a galaxy—and ultimately showered Earth with those telltale atoms.

    Erupting from hundreds of light-years away, the flash of x-rays and gamma rays probably did no harm on Earth.

    But the expanding fireball also accelerated cosmic rays—mostly nuclei of hydrogen and helium—to close to the speed of light. These projectiles arrived stealthily, decades later, ramping up into an invisible fusillade that could have lasted for thousands of years and might have affected the atmosphere—and life.

    In a flurry of studies and speculation, astronomers have sketched out their potential effects. A cosmic ray barrage might have boosted mutation rates by eroding Earth’s protective ozone layer and generating showers of secondary, tissue-penetrating particles. Tearing through the atmosphere, the particles would have also created pathways for lightning, perhaps kindling a spate of wildfires. At the same time, atmospheric reactions triggered by the radiation could have led to a rain of nitrogen compounds, which would have fertilized plants, drawing down carbon dioxide. In that way, the celestial event could have cooled the climate and helped initiate the ice ages 2.5 million years ago, at the start of the Pleistocene epoch. Even taken together, the effects are “not like the dinosaur extinction event—it’s more subtle and local,” says Brian Thomas, an astronomer at Washburn University (US) who has studied the earthly effects of cosmic catastrophes for nearly 2 decades.

    Few astronomers are suggesting that the supernovae caused any great extinction at the time, and even fewer paleontologists are ready to believe them. “Death from space is always really cool,” says Pincelli Hull, a paleontologist at Yale University (US). “The evidence is interesting but has not quite really reached the threshold to incorporate into my mental register.”

    Yet the supernova hunters believe other blasts, more distant in time, went off closer to Earth. And they think these supernovae could explain some extinction events that lack customary triggers such as volcanic outbursts or asteroid impacts. Adrian Melott, an astronomer at the University of Kansas-Lawrence (US), who explores how nearby cosmic cataclysms might affect Earth, says it’s time to more carefully probe Earth’s history for ancient supernova strikes. Not only will that help astrophysicists understand how the blasts shaped the neighborhood of the Solar System and seeded it with heavy elements, but it could also give paleontologists a new way to think about bouts of global change. “This is new and unfamiliar,” Melott says. “It will take time to be accepted.”

    Astronomers believe a few supernovae go off in the Milky Way every century. By the law of averages, a handful must have exploded very close to Earth—within 30 light-years—during its 4.5-billion-year lifetime, with potentially catastrophic effects. Even blasts as far as 300 light-years away should leave traces in the form of specks of dust blown out in the shell of debris known as a supernova remnant. When physicist Luis Alvarez set out in the 1970s with his geologist son Walter Alvarez to study the sediment layers associated with the dinosaurs’ extinction 65 million years ago, they were expecting to find supernova dust. Instead, they found iridium, an element that is rare on Earth’s surface but abundant in asteroids.

    The Alvarezes didn’t have the tools to look for supernova dust, in any case. Because Earth is already largely made of elements forged in supernovae billions of years ago, before the Sun’s birth, most traces of more recent explosions are undetectable. Not all of them, however. In the 1990s, astrophysicists realized supernova dust might also deposit radioactive isotopes with half-lives of millions of years, far too short to have been around since Earth’s birth. Any that are found must come from geologically recent sprinklings. One key tracer is iron-60 forged in the cores of large stars-which has a half-life of 2.6 million years and is not made naturally on Earth.

    In the late 1990s, Gunther Korschinek, an astroparticle physicist at the Technical University of Munich [Technische Universität München] (DE), decided to look for it, partly because the university had a powerful accelerator mass spectrometer (ASM) suited to the task. After ionizing a sample, an ASM boosts the charged particles to high energies and shoots them through a magnetic field. The field bends their path onto a string of detectors; the heaviest atoms are deflected least because of their greater momentum.

    Separating atoms of iron-60 from the similarly hefty but differently charged nickel-60 is especially challenging, but TUM’s ASM, built in 1970, is one of the few in the world powerful enough to tease them apart.

    Korschinek also needed the right sample: a geologic deposit laid down over millions of years in which an iron signal might stand out. Antarctic ice cores wouldn’t work: they only go back a couple of million years or so. Most ocean sediments accumulate so fast that any iron-60 is diluted to undetectable levels. Korschinek ended up using a ferromanganese crust dredged from a North Pacific seamount by the German research ship Valdivia in 1976. These crusts grow on patches of seabed where sediments can’t settle because of a slope or currents. When the pH of the water is just right, metal atoms selectively precipitate out of the water, slowly building up a mineral crust at the rate of a few millimeters every million years.

    Korschinek and his team sliced their sample up into layers of different ages, chemically separated out the iron, and fired the atoms through their mass spectrometer. They found 23 atoms of iron-60 among the thousands of trillions of atoms of normal iron, with the highest abundance from a time less than 3 million years ago, the team reported in Physical Review Letters in 1999. The era of supernova geochemistry had begun. “We were the first ones to start experimental studies,” Korschinek says.

    Others followed. Iron-60 was found in ocean crusts from other parts of the world and even in ocean sediment microfossils, remains of living things that, helpfully for the supernovae hunters, had taken up and concentrated iron in their bodies. Most results pointed to a local supernova between 2 million and 3 million years ago—with hints of a second one a few million years earlier.

    Although the remnants from these blasts have long since swept past Earth, a drizzle of the atoms they blew out continues. In 2019, Korschinek’s team ran iron from a half-ton of fresh Antarctic snow through its ASM and found a handful of iron-60 atoms, which he estimates fell to Earth in the past 20 years. Another team found a smattering of the atoms in cosmic rays detected by NASA’s Advanced Composition Explorer at a position partway between the Sun and Earth.

    Researchers have even found iron-60 in lunar soil brought back by the Apollo missions. “The Moon confirmed that it was not just some Earth-based phenomenon,” says astronomer Adrienne Ertel of the University of Illinois, Urbana-Champaign (US).

    2
    To detect trace ions, an Australian accelerator fired samples through a magnet.
    Tim Wetherell/Research School of Physics/Australian National University (AU).

    Dieter Breitschwerdt is trying to trace the iron to its source in the sky. When the astronomer at the Technical University of Berlin [Technische Universität Berlin](DE) learned of Korschinek’s results, he was studying the local bubble, a region of space around the Solar System swept clear of most of its gas and dust. Supernovae were the likely brooms, and so he began to track gangs of stars in the Solar System’s neighborhood to see whether any passed close enough to the Sun to deposit iron-60 on Earth when some of their members exploded.

    Using data from Hipparcos, a European star-mapping satellite, Breitschwerdt looked for clumps of stars on common trajectories and rewound the clock to see where they would have been millions of years ago.

    Two clumps, now a part of the Scorpius-Centaurus OB Association (Sco OB2), seemed to be in the perfect spot—300 light-years from Earth—about 2.5 million years ago. “It looked like a miracle,” he says. The odds of a detonation at the right time were good. Core-collapse supernovae take place in massive stars. Based on the ages and masses of the 79 stars remaining in the clumps, Breitschwerdt estimates that a dozen former members exploded as supernovae in the past 13 million years.

    Visible evidence for these supernovae in Sco OB2 is long gone: Supernova remnants dissipate after about 30,000 years, and the black holes or neutron stars they leave behind are challenging to spot. But the arrival direction of the iron dust could, in theory, point back to its source. Samples from the sea floor provide no directional information because wind and ocean currents move the dust as it settles. On the Moon, however, “there is no atmosphere, so where it hits is where it stops,” says UIUC astronomer Brian Fields. Because it spins, the Moon cannot provide longitudinal direction, but if more iron-60 was detected at one of the poles than at the equator, for example, that could support Breitschwerdt’s Sco OB2 as the source. Fields and several colleagues want to test that idea and have applied to NASA for samples of lunar soil, to be collected and returned by any future robotic or human missions.

    Korschinek’s team now has a rival in the hunt for supernova iron: a group led by Anton Wallner, a former postdoc of Korschinek’s, who has used an upgraded ASM at Australian National University (AU) to analyze several ferromanganese crusts dredged off the Pacific Ocean floor by a Japanese mining company. “Now we pushed Munich,” Wallner says.

    This year, in Science Advances[sorry, no link] Wallner’s team probed the timing of the recent supernovae more precisely than ever by slicing a crust sample into 24 1-millimeter-thick layers, each representing 400,000 years. “It’s never been done before with this time resolution,” says Wallner, now at the Helmholtz Center Dresden-Rossendorf [Helmholtz-Zentrum Dresden-Rossendorf](DE). The 435 iron-60 atoms they extracted pinned the most recent supernova at 2.5 million years ago and confirmed the hints of an earlier one, which they pegged at 6.3 million years ago. Comparing the abundance of iron-60 in the crust with models of how much a supernova produces, the team estimated the distance of these supernovae as between 160 and 320 light-years from Earth.

    Wallner’s team also found 181 atoms of plutonium-244, another radioactive isotope, but one that may have been forged in the supernova blast itself rather than in the precursor star, like iron-60. But its source is hotly debated: Some researchers think plutonium-244 is tough for supernovae to make in any great amounts. Instead, they see it as the product of collisions between neutron stars—cinders left behind by supernovae [Science].

    These collisions, called kilonovae, are 100 times rarer than supernovae, but are much more efficient at making the heaviest elements. “Neutron star mergers have an easy time making plutonium,” says Rebecca Surman, an astrophysicist at the University of Notre Dame. “For supernovae it’s much harder.”

    Surman still sees a role for supernovae. She takes the reported seafloor plutonium-244 as a sign that a kilonova, deep in the past, dusted our interstellar neighborhood with heavy elements. When the two recent supernovae went off, their expanding remnants may have swept up and delivered some of that interstellar plutonium-244 along with their own iron-60, she speculates. Korschinek, however, says it will take more data on the plutonium signal and its timing to convince him that multiple rare events happened so near and so recently.

    Beyond dusting Earth with rare nuclei, what impact might nearby supernovae have had? In 2016, a team led by Melott and Thomas estimated the flux of various forms of light and cosmic rays likely to reach Earth from an explosion 300 light-years away. Writing in The Astrophysical Journal Letters, they concluded that the most energetic, potentially damaging photons—x-rays or gamma rays—would have minimal impact. “There is not a lot of high energy radiation,” Thomas says. They suggested a few weeks of the bright light would have little more impact than disrupting sleep patterns.

    Cosmic rays—the particles accelerated to near light speed by shock waves in the supernova’s expanding fireball—are another story. Because they are charged, they can be deflected away from Earth by galactic magnetic fields. But the local bubble is thought to be mostly devoid of fields, so cosmic rays from just 300 light-years away would have a relatively clean shot.

    The atmosphere would have been subjected to a drawn-out barrage, Melott and Thomas found. “The ramp up is a slow process, decades at least,” Thomas says, reaching a peak about 500 years after the supernova flash and causing a 10-fold increase in ionization of atmospheric gas that would persist for 5000 years. Using an atmospheric chemistry model developed by NASA, they estimated that chemical changes caused by the ionization would deplete ozone by about 7% or more in places and would boost the creation of fertilizing nitrogen oxide compounds by 30%. The resulting surge in plants might be enough to cool the climate and usher in the Pleistocene.

    The cosmic rays weren’t done yet. When high-energy particles hit the upper atmosphere, they create cascades of secondary particles. Most fizzle out in further collisions, but muons—heavy short-lived cousins of electrons—keep going. Creatures on Earth’s surface would receive triple the normal radiation dose—equivalent to one or two CT scans per year. “An enhanced risk [of cancer], but not radiation poisoning,” Thomas says. Overall, the team thought the effects were “not catastrophic” but could be detectable in the fossil record if, for example, certain vulnerable species disappeared while others survived.

    In Astrobiology in 2019, Melott and two colleagues found that if the supernova exploded just 150 light-years away, rather than 300, the muon radiation would have hit marine animals surprisingly hard. Water blocks most particles that rain down from the sky, but muons can penetrate up to 1 kilometer. Marine creatures, normally shielded from nearly all radiation, would experience the largest relative increase in dose and suffer the most. This chimes with an extinction of marine megafauna at the start of the Pleistocene epoch, only recently identified in the fossil record.

    Then, last year, supernova proponents suggested a similar scenario could explain a major extinction event 359 million years ago, at the end of the Devonian period. A team led by John Marshall of the University of Southampton (UK) had found that the spores of fernlike plants from the time suddenly became misshapen and dark, blaming the changes on ultraviolet radiation. The team didn’t invoke an astronomical cause. But writing in the PNAS, astronomers saw the possible signature of a nearby supernova. They suggested a blast maybe just 60 light-years away could have drenched Earth in ultraviolet by depleting the ozone layer. “It’s pretty speculative,” admits co-author John Ellis, a theorist at King’s College London (UK), as it is currently impossible to identify the radioactive fingerprints of a supernova that far back.

    In a 2020 paper in The Journal of Geology, Melott and Thomas took a bigger speculative leap. They noted that by ripping electrons from air molecules, secondary cosmic rays would have created pathways for lightning, making storms more likely, which would not only generate more nitrogen compounds but also spark wildfires. Intriguingly, a layer of soot has been found in the rock record in some parts of the world at the start of the Pleistocene. Melott and Thomas went on to suggest that those supernova-induced forest fires may have pushed early humans out of the trees and onto the savanna, leading to bipedalism, larger brain size, and everything that followed. “It’s fascinating to say that a supernova 2.5 million years ago means we are talking now via Skype,” Korschinek says.

    Such scenarios don’t sit well with paleontologists. “Timing is the trivial answer to everything,” Hull says. “There’s always something happening when things become extinct.” Besides, she says, the transition to the Pleistocene “doesn’t stand out as needing an explanation.” She says other events around that time could have had more impact on the global climate, such as the closing of the isthmus of Panama, which profoundly changed ocean circulation.

    To make their case, she says, astronomers need to pin down the timing of the ancient supernovae more precisely. They “need to measure more crusts.” But hunting for supernova traces is not getting any easier. In 2019 TUM closed its AMS, leaving only ANU with an accelerator powerful enough to separate iron-60.

    In contrast, rarer isotopes such as plutonium-244 could enable researchers to look further back in time, but they require an AMS that emphasizes sensitivity rather than raw power, and Wallner says only a few in the world are up to the job. He has secured funding to build a new AMS facility in Dresden, Germany, specializing in the heaviest elements, that should be open by 2023. To renew the hunt for iron-60, his team has also made a pitch for national funding to build a new high-energy AMS, which could be up and running in 7 years.

    For astronomers, a sudden flash of light in the sky today would be the best chance to see how supernova affects Earth. But the odds are slim that we will see a light show like the one that may have dazzled our distant ancestors. Betelgeuse, a restive red giant likely to blow up sometime in the next 100,000 years, has settled down in recent months, and in any case, it lies more than 500 light-years away. Sco OB2 is now heading away from the Sun. And using data from Hipparcos’s successor, Europe’s Gaia mission, Breitschwerdt has tracked another 10 clumps of stars.

    “None are coming closer,” he says. “The future”—for Earth, not the supernovae—“is bright.”

    See the full article here .


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  • richardmitnick 11:32 am on November 15, 2020 Permalink | Reply
    Tags: , , , , , , , , , Supernovae, U Rochester OMEGA Laser Facility   

    From From DOE’s Lawrence Livermore National Laboratory via Science News: “Giant lasers help re-create supernovas’ explosive, mysterious physics” 

    From DOE’s Lawrence Livermore National Laboratory

    via

    Science News

    November 12, 2020
    Emily Conover

    1
    Researchers are re-creating the physics of cosmic explosions using the world’s most energetic lasers, such as the one at OMEGA (shown) at the University of Rochester in New York. Credit: Eugene Kowaluk/Univ. of Rochester Laboratory for Laser Energetics.

    Pocket-sized blasts in the lab reveal details of massive stellar explosions.

    When one of Hye-Sook Park’s experiments goes well, everyone nearby knows. “We can hear Hye-Sook screaming,” she’s heard colleagues say.

    Science paper:
    Electron acceleration in laboratory-produced turbulent collisionless shocks
    Nature Physics

    It’s no surprise that she can’t contain her excitement. She’s getting a closeup look at the physics of exploding stars, or supernovas, a phenomenon so immense that its power is difficult to put into words.

    Rather than studying these explosions from a distance through telescopes, Park, a physicist at Lawrence Livermore National Laboratory in California, creates something akin to these paroxysmal blasts using the world’s highest-energy lasers.

    About 10 years ago, Park and colleagues embarked on a quest to understand a fascinating and poorly understood feature of supernovas: Shock waves that form in the wake of the explosions can boost particles, such as protons and electrons, to extreme energies.

    “Supernova shocks are considered to be some of the most powerful particle accelerators in the universe,” says plasma physicist Frederico Fiuza of SLAC National Accelerator Laboratory in Menlo Park, Calif., one of Park’s collaborators.

    Some of those particles eventually slam into Earth, after a fast-paced marathon across cosmic distances. Scientists have long puzzled over how such waves give energetic particles their massive speed boosts. Now, Park and colleagues have finally created a supernova-style shock wave in the lab and watched it send particles hurtling, revealing possible new hints about how that happens in the cosmos.

    Bringing supernova physics down to Earth could help resolve other mysteries of the universe, such as the origins of cosmic magnetic fields. And there’s a more existential reason physicists are fascinated by supernovas. These blasts provide some of the basic building blocks necessary for our existence. “The iron in our blood comes from supernovae,” says plasma physicist Carolyn Kuranz of the University of Michigan in Ann Arbor, who also studies supernovas in the laboratory. “We’re literally created from stars.”

    Lucky star

    As a graduate student in the 1980s, Park worked on an experiment 600 meters underground in a working salt mine beneath Lake Erie in Ohio. Called IMB for Irvine-Michigan-Brookhaven, the experiment wasn’t designed to study supernovas. But the researchers had a stroke of luck. A star exploded in a satellite galaxy of the Milky Way, and IMB captured particles catapulted from that eruption. Those messengers from the cosmic explosion, lightweight subatomic particles called neutrinos, revealed a wealth of new information about supernovas.

    But supernovas in our cosmic vicinity are rare. So decades later, Park isn’t waiting around for a second lucky event.

    2
    Physicist Hye-Sook Park, shown as a graduate student in the 1980s (left) and in a recent photo (right), uses powerful lasers to study astrophysics. Credit:from left John Van der Velde; Lanie L. Rivera/Lawrence Livermore National Laboratory.

    Instead, her team and others are using extremely powerful lasers to re-create the physics seen in the aftermath of supernova blasts. The lasers vaporize a small target, which can be made of various materials, such as plastic. The blow produces an explosion of fast-moving plasma, a mixture of charged particles, that mimics the behavior of plasma erupting from supernovas.

    The stellar explosions are triggered when a massive star exhausts its fuel and its core collapses and rebounds. Outer layers of the star blast outward in an explosion that can unleash more energy than will be released by the sun over its entire 10-billion-year lifetime. The outflow has an unfathomable 100 quintillion yottajoules of kinetic energy (SN: 2/8/17, p. 24).

    Supernovas can also occur when a dead star called a white dwarf is reignited, for example after slurping up gas from a companion star, causing a burst of nuclear reactions that spiral out of control (SN: 4/30/16, p. 20).

    3
    Supernova remnants like W49B (shown in X-ray, radio and infrared light) accelerate electrons and protons to high energies in shock waves. Credit: NASA, CXC, MIT L. Lopez et al (X-ray), Palomar (Infrared), VLA/NRAO/NSF (Radio)

    NASA Chandra X-ray Space Telescope

    Caltech Palomar 200 inch Hale Telescope, Altitude 1,713 m (5,620 ft), located in San Diego County, California, U.S.A.

    NRAO Karl G Jansky Very Large Array, located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~50 miles (80 km) west of Socorro. The VLA comprises twenty-eight 25-meter radio telescopes.

    In both cases, things really get cooking when the explosion sends a blast of plasma careening out of the star and into its environs, the interstellar medium — essentially, another ocean of plasma particles. Over time, a turbulent, expanding structure called a supernova remnant forms, begetting a beautiful light show, tens of light-years across, that can persist in the sky for many thousands of years after the initial explosion. It’s that roiling remnant that Park and colleagues are exploring.

    Studying supernova physics in the lab isn’t quite the same thing as the real deal, for obvious reasons. “We cannot really create a supernova in the laboratory, otherwise we would be all exploded,” Park says.

    In lieu of self-annihilation, Park and others focus on versions of supernovas that are scaled down, both in size and in time. And rather than reproducing the entirety of a supernova all at once, physicists try in each experiment to isolate interesting components of the physics taking place. Out of the immense complexity of a supernova, “we are studying just a tiny bit of that, really,” Park says.

    For explosions in space, scientists are at the mercy of nature. But in the laboratory, “you can change parameters and see how shocks react,” says astrophysicist Anatoly Spitkovsky of Princeton University, who collaborates with Park.

    The laboratory explosions happen in an instant and are tiny, just centimeters across. For example, in Kuranz’s experiments, the equivalent of 15 minutes in the life of a real supernova can take just 10 billionths of a second. And a section of a stellar explosion larger than the diameter of Earth can be shrunk down to 100 micrometers. “The processes that occur in both of those are very similar,” Kuranz says. “It blows my mind.”


    How to make a fake supernova | Science News
    Powerful, mysterious stellar explosions are difficult to understand from afar, so researchers have figured out how to re-create supernovas’ extreme physics in the lab and study how outbursts seed the cosmos with elements and energetic particles.

    Laser focus

    To replicate the physics of a supernova, laboratory explosions must create an extreme environment. For that, you need a really big laser, which can be found in only a few places in the world, such as NIF, the National Ignition Facility at Lawrence Livermore, and the OMEGA Laser Facility at the University of Rochester in New York.

    At both places, one laser is split into many beams. The biggest laser in the world, at NIF, has 192 beams. Each of those beams is amplified to increase its energy exponentially. Then, some or all of those beams are trained on a small, carefully designed target. NIF’s laser can deliver more than 500 trillion watts of power for a brief instant, momentarily outstripping the total power usage in the United States by a factor of a thousand.

    A single experiment at NIF or OMEGA, called a shot, is one blast from the laser. And each shot is a big production. Opportunities to use such advanced facilities are scarce, and researchers want to have all the details ironed out to be confident the experiment will be a success.

    When a shot is about to happen, there’s a space-launch vibe. Operators monitor the facility from a control room filled with screens. When the time of the laser blast nears, a voice begins counting down: “Ten, nine, eight …”

    “When they count down for your shot, your heart is pounding,” says plasma physicist Jena Meinecke of the University of Oxford, who has worked on experiments at NIF and other laser facilities.

    At the moment of the shot, “you kind of want the Earth to shake,” Kuranz says. But instead, you might just hear a snap — the sound of the discharge from capacitors that store up huge amounts of energy for each shot.

    Then comes a mad dash to review the results and determine if the experiment has been successful. “It’s a lot of adrenaline,” Kuranz says.

    NIL

    National Ignition Facility at DOE’s Lawrence Livermore National Laboratory.

    3
    At the National Ignition Facility’s target chamber (shown during maintenance), 192 laser beams converge. The blasts produce plumes of plasma that can mimic some aspects of supernova remnants.Credit: Lawrence Livermore National Laboratory.

    Lasers aren’t the only way to investigate supernova physics in the lab. Some researchers use intense bursts of electricity, called pulsed power. Others use small amounts of explosives to set off blasts. The various techniques can be used to understand different stages in supernovas’ lives.

    A real shocker

    Park brims with cosmic levels of enthusiasm, ready to erupt in response to a new nugget of data or a new success in her experiments. Re-creating some of the physics of a supernova in the lab really is as remarkable as it sounds, she says. “Other­wise I wouldn’t be working on it.” Along with Spitkovsky and Fiuza, Park is among more than a dozen scientists involved in the Astrophysical Collisionless Shock Experiments with Lasers collaboration, or ACSEL, the quest Park embarked upon a decade ago. Their focus is shock waves.

    The result of a violent input of energy, shock waves are marked by an abrupt increase in temperature, density and pressure. On Earth, shock waves cause the sonic boom of a supersonic jet, the clap of thunder in a storm and the damaging pressure wave that can shatter windows in the aftermath of a massive explosion. These shock waves form as air molecules slam into each other, piling up molecules into a high-density, high-pressure and high-temperature wave.

    In cosmic environments, shock waves occur not in air, but in plasma, a mixture of protons, electrons and ions, electrically charged atoms. There, particles may be diffuse enough that they don’t directly collide as they do in air. In such a plasma, the pileup of particles happens indirectly, the result of electromagnetic forces pushing and pulling the particles. “If a particle changes trajectory, it’s because it feels a magnetic field or an electric field,” says Gianluca Gregori, a physicist at the University of Oxford who is part of ACSEL.

    But exactly how those fields form and grow, and how such a shock wave results, has been hard to decipher. Researchers have no way to see the process in real supernovas; the details are too small to observe with telescopes.

    These shock waves, which are known as collisionless shock waves, fascinate physicists. “Particles in these shocks can reach amazing energies,” Spitkovsky says. In supernova remnants, particles can gain up to 1,000 trillion electron volts, vastly outstripping the several trillion electron volts reached in the biggest human-made particle accelerator, the Large Hadron Collider near Geneva. But how particles might surf supernova shock waves to attain their astounding energies has remained mysterious.

    Magnetic field origins

    To understand how supernova shock waves boost particles, you have to understand how shock waves form in supernova remnants. To get there, you have to understand how strong magnetic fields arise. Without them, the shock wave can’t form.

    Electric and magnetic fields are closely intertwined. When electrically charged particles move, they form tiny electric currents, which generate small magnetic fields. And magnetic fields themselves send charged particles corkscrewing, curving their trajectories. Moving magnetic fields also create electric fields.

    The result is a complex feedback process of jostling particles and fields, eventually producing a shock wave. “This is why it’s so fascinating. It’s a self-modulating, self-controlling, self-reproducing structure,” Spitkovsky says. “It’s like it’s almost alive.”

    All this complexity can develop only after a magnetic field forms. But the haphazard motions of individual particles generate only small, transient magnetic fields. To create a significant field, some process within a supernova remnant must reinforce and amplify the magnetic fields. A theoretical process called the Weibel instability, first thought up in 1959, has long been expected to do just that.

    In a supernova, the plasma streaming outward in the explosion meets the plasma of the interstellar medium. According to the theory behind the Weibel instability, the two sets of plasma break into filaments as they stream by one another, like two hands with fingers interlaced. Those filaments act like current-­carrying wires. And where there’s current, there’s a magnetic field. The filaments’ magnetic fields strengthen the currents, further enhancing the magnetic fields. Scientists suspected that the electromagnetic fields could then become strong enough to reroute and slow down particles, causing them to pile up into a shock wave.

    In 2015 in Nature Physics, the ACSEL team reported a glimpse of the Weibel instability in an experiment at OMEGA. The researchers spotted magnetic fields, but didn’t directly detect the filaments of current. Finally, this year, in the May 29 Physical Review Letters, the team reported that a new experiment had produced the first direct measurements of the currents that form as a result of the Weibel instability, confirming scientists’ ideas about how strong magnetic fields could form in supernova remnants.

    For that new experiment, also at OMEGA, ACSEL researchers blasted seven lasers each at two targets facing each other. That resulted in two streams of plasma flowing toward each other at up to 1,500 kilometers per second — a speed fast enough to circle the Earth twice in less than a minute. When the two streams met, they separated into filaments of current, just as expected, producing magnetic fields of 30 tesla, about 20 times the strength of the magnetic fields in many MRI machines.

    “What we found was basically this textbook picture that has been out there for 60 years, and now we finally were able to see it experimentally,” Fiuza says.

    Surfing a shock wave

    Once the researchers had seen magnetic fields, the next step was to create a shock wave and to observe it accelerating particles. But, Park says, “no matter how much we tried on OMEGA, we couldn’t create the shock.”

    They needed the National Ignition Facility and its bigger laser.

    There, the researchers hit two disk-shaped targets with 84 laser beams each, or nearly half a million joules of energy, about the same as the kinetic energy of a car careening down a highway at 60 miles per hour.

    Two streams of plasma surged toward each other. The density and temperature of the plasma rose where the two collided, the researchers reported in the September Nature Physics. “No doubt about it,” Park says. The group had seen a shock wave, specifically the collisionless type found in supernovas. In fact there were two shock waves, each moving away from the other.

    4
    Credit: F. Fiuza et al/Nature Physics 2020.

    Learning the results sparked a moment of joyous celebration, Park says: high fives to everyone.

    “This is some of the first experimental evidence of the formation of these collisionless shocks,” says plasma physicist Francisco Suzuki-Vidal of Imperial College London, who was not involved in the study. “This is something that has been really hard to reproduce in the laboratory.”

    The team also discovered that electrons had been accelerated by the shock waves, reaching energies more than 100 times as high as those of particles in the ambient plasma. For the first time, scientists had watched particles surfing shock waves like the ones found in supernova remnants.

    But the group still didn’t understand how that was happening.

    In a supernova remnant and in the experiment, a small number of particles are accelerated when they cross over the shock wave, going back and forth repeatedly to build up energy. But to cross the shock wave, the electrons need some energy to start with. It’s like a big-wave surfer attempting to catch a massive swell, Fiuza says. There’s no way to catch such a big wave by simply paddling. But with the energy provided by a Jet Ski towing surfers into place, they can take advantage of the wave’s energy and ride the swell.

    4
    A computer simulation of a shock wave (structure shown in blue) illustrates how electrons gain energy (red tracks are higher energy, yellow and green are lower).Credit: F. Fiuza/SLAC National Accelerator Laboratory.

    “What we are trying to understand is: What is our Jet Ski? What happens in this environment that allows these tiny electrons to become energetic enough that they can then ride this wave and be accelerated in the process?” Fiuza says.

    The researchers performed computer simulations that suggested the shock wave has a transition region in which magnetic fields become turbulent and messy. That hints that the turbulent field is the Jet Ski: Some of the particles scatter in it, giving them enough energy to cross the shock wave.

    Wake-up call

    Enormous laser facilities such as NIF and OMEGA are typically built to study nuclear fusion — the same source of energy that powers the sun. Using lasers to compress and heat a target can cause nuclei to fuse with one another, releasing energy in the process. The hope is that such research could lead to fusion power plants, which could provide energy without emitting greenhouse gases or dangerous nuclear waste (SN: 4/20/13, p. 26). But so far, scientists have yet to get more energy out of the fusion than they put in — a necessity for practical power generation.

    So these laser facilities dedicate many of their experiments to chasing fusion power. But sometimes, researchers like Park get the chance to study questions based not on solving the world’s energy crisis, but on curiosity — wondering what happens when a star explodes, for example. Still, in a roundabout way, understanding supernovas could help make fusion power a reality as well, as that celestial plasma exhibits some of the same behaviors as the plasma in fusion reactors.

    At NIF, Park has also worked on fusion experiments. She has studied a wide variety of topics since her grad school days, from working on the U.S. “Star Wars” missile defense program, to designing a camera for a satellite sent to the moon, to looking for the sources of high-energy cosmic light flares called gamma-ray bursts. Although she is passionate about each topic, “out of all those projects,” she says, “this particular collisionless shock project happens to be my love.”

    Early in her career, back on that experiment in the salt mine, Park got a first taste of the thrill of discovery. Even before IMB captured neutrinos from a supernova, a different unexpected neutrino popped up in the detector. The particle had passed through the entire Earth to reach the experiment from the bottom. Park found the neutrino while analyzing data at 4 a.m., and woke up all her collaborators to tell them about it. It was the first time anyone working on the experiment had seen a particle coming up from below. “I still clearly remember the time when I was seeing something nobody’s seen,” Park recalls.

    Now, she says, she still gets the same feeling. Screams of joy erupt when she sees something new that describes the physics of unimaginably vast explosions.

    See the full article here .


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    Operated by Lawrence Livermore National Security, LLC, for the Department of Energy’s National Nuclear Security Administration
    Lawrence Livermore National Laboratory (LLNL) is an American federal research facility in Livermore, California, United States, founded by the University of California, Berkeley in 1952. A Federally Funded Research and Development Center (FFRDC), it is primarily funded by the U.S. Department of Energy (DOE) and managed and operated by Lawrence Livermore National Security, LLC (LLNS), a partnership of the University of California, Bechtel, BWX Technologies, AECOM, and Battelle Memorial Institute in affiliation with the Texas A&M University System. In 2012, the laboratory had the synthetic chemical element livermorium named after it.
    LLNL is self-described as “a premier research and development institution for science and technology applied to national security.” Its principal responsibility is ensuring the safety, security and reliability of the nation’s nuclear weapons through the application of advanced science, engineering and technology. The Laboratory also applies its special expertise and multidisciplinary capabilities to preventing the proliferation and use of weapons of mass destruction, bolstering homeland security and solving other nationally important problems, including energy and environmental security, basic science and economic competitiveness.

    The Laboratory is located on a one-square-mile (2.6 km2) site at the eastern edge of Livermore. It also operates a 7,000 acres (28 km2) remote experimental test site, called Site 300, situated about 15 miles (24 km) southeast of the main lab site. LLNL has an annual budget of about $1.5 billion and a staff of roughly 5,800 employees.

    LLNL was established in 1952 as the University of California Radiation Laboratory at Livermore, an offshoot of the existing UC Radiation Laboratory at Berkeley. It was intended to spur innovation and provide competition to the nuclear weapon design laboratory at Los Alamos in New Mexico, home of the Manhattan Project that developed the first atomic weapons. Edward Teller and Ernest Lawrence,[2] director of the Radiation Laboratory at Berkeley, are regarded as the co-founders of the Livermore facility.

    The new laboratory was sited at a former naval air station of World War II. It was already home to several UC Radiation Laboratory projects that were too large for its location in the Berkeley Hills above the UC campus, including one of the first experiments in the magnetic approach to confined

     
  • richardmitnick 10:37 pm on October 12, 2020 Permalink | Reply
    Tags: An Australian-led team confirms and explains a new member of an elite club that breaks all the rules., Apep Wolf-Rayet binary pair, , , , , , One in a hundred million stars is a Wolf-Rayet., Rare even among Wolf-Rayets are elegant binary pairs that if the conditions are right are able to pump out huge amounts of carbon dust driven by their extreme stellar winds., Supernovae, U Sydney   

    From University of Sidney AU via COSMOS Magazine AU: “Astronomers report two new space oddities” one from U Sydney 

    U Sidney bloc

    From University of Sidney AU

    via

    Cosmos Magazine bloc

    COSMOS Magazine AU

    13 October 2020

    Australian-led team confirms and explains a new member of an elite club that breaks all the rules.

    In, MNRAS, an Australian-led team, confirms and explains a new member of an elite club that breaks all the rules.

    1
    Infrared image of Apep. Credit: European Southern Observatory EU.

    One in a hundred million stars is a Wolf-Rayet: hot and very bright but doomed to imminent collapse in a supernova explosion leaving only a dark remnant, such as a black hole. Rare even among Wolf-Rayets are elegant binary pairs that, if the conditions are right, are able to pump out huge amounts of carbon dust driven by their extreme stellar winds.

    As the two stars orbit one another, the dust gets wrapped into a beautiful glowing sooty tail. Just a handful of these sculpted spiral plumes has ever been discovered.

    Researchers led by Peter Tuthill, from the University of Sydney, found one 8000 light-years from Earth two years ago and called it Apep. They were stumped, however, by the expansion of its dust spiral.

    “The dust seems to have a mind of its own, floating along much slower than the extreme stellar winds that should be driving it,” says Yinuo Han, lead author of the new paper that describes the strange physics.

    Using the VLT, he and colleagues produced a model that matches the intricate dust spiral structure for the first time, revealing that it is expanding at only a quarter the speed of the measured stellar winds, something they say is unheard of in other systems.

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo.

    The leading theory to explain this behaviour, they suggest, makes Apep a strong contender for producing a gamma-ray burst when it does finally explode, something never before witnessed in the Milky Way.

    Gamma-ray burst credit NASA SWIFT/Cruz Dewilde.

    “There has been a flurry of research into Wolf-Rayet star systems: these really are the peacocks of the stellar world,” says co-author Joe Callingham, from Leiden University in the Netherlands.

    “Discoveries about these elegantly beautiful, but potentially dangerous objects, [are] causing a real buzz in astronomy.”

    The numbers reveal Apep’s extreme nature. The two stars are each about 10 to 15 times more massive than the Sun and more than 100,000 times brighter. They orbit each other about every 125 years at a distance comparable to the size of our Solar System.

    See the full article here.

    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Sidney campus

    University of Sydney AU
    Our founding principle as Australia’s first university was that we would be a modern and progressive institution. It’s an ideal we still hold dear today.

    When Charles William Wentworth proposed the idea of Australia’s first university in 1850, he imagined “the opportunity for the child of every class to become great and useful in the destinies of this country”.

    We’ve stayed true to that original value and purpose by promoting inclusion and diversity for the past 160 years.

    It’s the reason that, as early as 1881, we admitted women on an equal footing to male students. Oxford University didn’t follow suit until 30 years later, and Jesus College at Cambridge University did not begin admitting female students until 1974.

    It’s also why, from the very start, talented students of all backgrounds were given the chance to access further education through bursaries and scholarships.

    Today we offer hundreds of scholarships to support and encourage talented students, and a range of grants and bursaries to those who need a financial helping hand.

     
  • richardmitnick 8:14 pm on July 15, 2020 Permalink | Reply
    Tags: "Nuclear blast sends star hurtling across galaxy", A star has been sent hurtling across the galaxy after undergoing a partial supernova astronomers say., , , , , , It sent the star hurtling through space at 900000 km/hr., SDSSJ1240+6710 may be the survivor of a type of supernova that hasn't yet been observed as it's happening., Supernovae, The blast was not sufficient to destroy it.,   

    From University of Warwick via BBC: “Nuclear blast sends star hurtling across galaxy” 

    From University of Warwick
    via

    BBC

    15 July 2020
    Paul Rincon

    1
    A star has been sent hurtling across the galaxy after undergoing a partial supernova, astronomers say.

    A supernova is a powerful explosion that occurs when some stars reach the ends of their lives; in this case, the blast was not sufficient to destroy it.

    Instead, it sent the star hurtling through space at 900,000 km/hr.

    Astronomers think the object, known as a white dwarf, was originally circling another star, which would have been sent flying in the opposite direction.

    When two stars orbit each other like this, they are described as a “binary”. Only one of the stars has been detected by astronomers, however.

    The object, known as SDSS J1240+6710, was previously found to have an unusual atmospheric composition.

    Discovered in 2015, it seemed to contain neither hydrogen nor helium (which are usually found), appearing to be composed instead of an unusual mix of oxygen, neon, magnesium and silicon.

    Mystery over monster star’s vanishing act

    Nearby ‘supernova’ star’s dimming explained

    Now, using the Hubble Space Telescope, an international team has also identified carbon, sodium, and aluminium in the star’s atmosphere, all of which are produced in the first thermonuclear reactions of a supernova.

    But there is also a clear absence of what is known as the “iron group” of elements, iron, nickel, chromium and manganese.

    These heavier elements are normally cooked up from the lighter ones, and make up the defining features of thermonuclear supernovas.

    The lack of iron group elements in SDSSJ1240+6710 suggests that the star only underwent a partial supernova before the nuclear burning died out.

    Lead author Professor Boris Gänsicke, from the department of physics at the University of Warwick, UK, said: “This star is unique because it has all the key features of a white dwarf but it has this very high velocity and unusual abundances that make no sense when combined with its low mass.

    “It has a chemical composition which is the fingerprint of nuclear burning, a low mass and a very high velocity; all of these facts imply that it must have come from some kind of close binary system and it must have undergone thermonuclear ignition. It would have been a type of supernova, but of a kind that that we haven’t seen before.”

    The high velocity could be accounted for if both stars in the binary were carried off in opposite directions at their orbital velocities in a kind of slingshot manoeuvre after the explosion.

    The scientists were also able to measure the star’s mass, which is particularly low for a white dwarf – only 40% the mass of our Sun – which would be consistent with a partial supernova that did not quite destroy the star.

    The nature of the nuclear burning that occurs in a supernova is different from the reactions that release energy in nuclear power plants or most nuclear weapons. Most uses of nuclear energy on Earth rely on fission – which breaks down heavier elements into lighter ones – rather than the fusion that occurs in a star.

    “The process developing during a thermonuclear supernova is very similar to what we try to achieve on Earth in our future power plants: nuclear fusion of lighter elements into heavier ones, which releases vast amounts of energy,” Prof Gänsicke told BBC News.

    “In a fusion reactor, we use the lightest element, hydrogen (more specifically, different flavours, or isotopes of it). In a thermonuclear supernova, the density and temperature in the star becomes so high that fusion of heavier elements ignites, starting with carbon and oxygen as ‘fuel’, and fusing heavier and heavier elements.”

    The best studied thermonuclear supernovas are classified as Type Ia. These helped lead to the discovery of dark energy, and are now routinely used to map the structure of the Universe. But there is growing evidence that thermonuclear supernovas can happen under very different conditions.

    SDSSJ1240+6710 may be the survivor of a type of supernova that hasn’t yet been observed as it’s happening.

    Without the radioactive nickel that powers the long-lasting afterglow of the Type Ia supernovas, the explosion that sent the white dwarf careering across our Galaxy would have been a brief flash of light that would have been difficult to discover.

    The research has been published in the MNRAS.

    See the full article here .

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    Stem Education Coalition

    The establishment of the The University of Warwick was given approval by the government in 1961 and received its Royal Charter of Incorporation in 1965.

    The idea for a university in Coventry was mooted shortly after the conclusion of the Second World War but it was a bold and imaginative partnership of the City and the County which brought the University into being on a 400-acre site jointly granted by the two authorities. Since then, the University has incorporated the former Coventry College of Education in 1978 and has extended its land holdings by the purchase of adjoining farm land.

    The University initially admitted a small intake of graduate students in 1964 and took its first 450 undergraduates in October 1965. In October 2013, the student population was over 23,000 of which 9,775 are postgraduates. Around a third of the student body comes from overseas and over 120 countries are represented on the campus.

     
  • richardmitnick 9:52 am on February 29, 2020 Permalink | Reply
    Tags: , , , Betelgeuse is dying., Betelgeuse' supernova could produce a dazzling display that could be visible even in daylight., , Supernovae, The red supergiant is nearing the end of its life and when a star over 10 times the mass of the Sun dies it goes out in spectacular fashion.,   

    From UC Santa Barbara: “A Massive Star’s Dying Breaths” 

    UC Santa Barbara Name bloc
    From UC Santa Barbara

    February 28, 2020
    Harrison Tasoff
    (805) 893-7220
    harrisontasoff@ucsb.edu

    1
    Supernovae are stupendously energetic; many can briefly outshine an entire galaxy. Artist’s impression.
    Photo Credit: ESO/M. Kornmesser.

    Betelgeuse has been the center of significant media attention lately. The red supergiant is nearing the end of its life, and when a star over 10 times the mass of the Sun dies, it goes out in spectacular fashion. With its brightness recently dipping to the lowest point in the last hundred years, many space enthusiasts are excited that Betelgeuse may soon go supernova, exploding in a dazzling display that could be visible even in daylight.

    While the famous star in Orion’s shoulder will likely meet its demise within the next million years — practically couple days in cosmic time — scientists maintain that its dimming is due to the star pulsating. The phenomenon is relatively common among red supergiants, and Betelgeuse has been known for decades to be in this group.

    Coincidentally, researchers at UC Santa Barbara have already made predictions about the brightness of the supernova that would result when a pulsating star like Betelgeuse explodes.

    Physics graduate student Jared Goldberg has published a study with Lars Bildsten, director of the campus’s Kavli Institute for Theoretical Physics (KITP) and Gluck Professor of Physics, and KITP Senior Fellow Bill Paxton detailing how a star’s pulsation will affect the ensuing explosion when it does reach the end. The paper appears in The Astrophysical Journal.

    “We wanted to know what it looks like if a pulsating star explodes at different phases of pulsation,” said Goldberg, a National Science Foundation graduate research fellow. “Earlier models are simpler because they don’t include the time-dependent effects of pulsations.”

    When a star the size of Betelgeuse finally runs out of material to fuse in its center, it loses the outward pressure that kept it from collapsing under its own immense weight. The resultant core collapse happens in half a second, far faster than it takes the star’s surface and puffy outer layers to notice.

    As the iron core collapses the atoms disassociate into electrons and protons. These combine to form neutrons, and in the process release high-energy particles called neutrinos. Normally, neutrinos barely interact with other matter — 100 trillion of them pass through your body every second without a single collision. That said, supernovae are among the most powerful phenomena in the universe. The numbers and energies of the neutrinos produced in the core collapse are so immense that even though only a tiny fraction collides with the stellar material, it’s generally more than enough to launch a shockwave capable of exploding the star.

    That resulting explosion smacks into the star’s outer layers with stupefying energy, creating a burst that can briefly outshine an entire galaxy. The explosion remains bright for around 100 days, since the radiation can escape only once ionized hydrogen recombines with lost electrons to become neutral again. This proceeds from the outside in, meaning that astronomers see deeper into the supernova as time goes on until finally the light from the center can escape. At that point, all that’s left is the dim glow of radioactive fallout, which can continue to shine for years.

    A supernova’s characteristics vary with the star’s mass, total explosion energy and, importantly, its radius. This means Betelgeuse’s pulsation makes predicting how it will explode rather more complicated.

    The researchers found that if the entire star is pulsating in unison — breathing in and out, if you will — the supernova will behave as though Betelgeuse was a static star with a given radius. However, different layers of the star can oscillate opposite each other: the outer layers expand while the middle layers contract, and vice versa.

    For the simple pulsation case, the team’s model yielded similar results to the models that didn’t account for pulsation. “It just looks like a supernova from a bigger star or a smaller star at different points in the pulsation,” Goldberg explained. “It’s when you start considering pulsations that are more complicated, where there’s stuff moving in at the same time as stuff moving out — then our model actually does produce noticeable differences,” he said.

    In these cases, the researchers discovered that as light leaks out from progressively deeper layers of the explosion, the emissions would appear as though they were the result of supernovae from different sized stars.

    “Light from the part of the star that is compressed is fainter,” Goldberg explained, “just as we would expect from a more compact, non-pulsating star.” Meanwhile, light from parts of the star that were expanding at the time would appear brighter, as though it came from a larger, non-pulsating star.

    Goldberg plans to submit a report to Research Notes of the American Astronomical Society with Andy Howell, a professor of physics, and KITP postdoctoral researcher Evan Bauer summarizing the results of simulations they ran specifically on Betelgeuse. Goldberg is also working with KITP postdoc Benny Tsang to compare different radiative transfer techniques for supernovae, and with physics graduate student Daichi Hiramatsu on comparing theoretical explosion models to supernova observations.

    See the full article here .

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    Stem Education CoalitionUC Santa Barbara Seal
    The University of California, Santa Barbara (commonly referred to as UC Santa Barbara or UCSB) is a public research university and one of the 10 general campuses of the University of California system. Founded in 1891 as an independent teachers’ college, UCSB joined the University of California system in 1944 and is the third-oldest general-education campus in the system. The university is a comprehensive doctoral university and is organized into five colleges offering 87 undergraduate degrees and 55 graduate degrees. In 2012, UCSB was ranked 41st among “National Universities” and 10th among public universities by U.S. News & World Report. UCSB houses twelve national research centers, including the renowned Kavli Institute for Theoretical Physics.

     
  • richardmitnick 2:18 pm on January 25, 2020 Permalink | Reply
    Tags: "The Biggest Celestial Event of the Year Could Happen Tomorrow", , , , , , Supernovae,   

    From The Atlantic Magazine: “The Biggest Celestial Event of the Year Could Happen Tomorrow” 

    Atlantic Magazine

    From The Atlantic Magazine

    … or, well, maybe not for 100,000 years.

    January 23, 2020
    Marina Koren

    1
    The constellation Orion, with Betelgeuse glowing orangeVW Pics / Universal Images Group / Getty

    Sometime this week, you might walk outside in broad daylight, look up at the sky, and see a luminous orb as bright as a full moon. Only it wouldn’t be the moon. It would be something far more explosive: the dazzling aftermath of a cataclysm hundreds of light-years away.

    You’d be seeing the light from a supernova—the final, powerful flash of a dying star.

    Or … you might see the regular old sky. Supernovas are nearly impossible to predict. But astronomers have recently started discussing the rare possibility with a bit more enthusiasm than usual, thanks to some odd behavior elsewhere in the Milky Way. If the supernova did show up tomorrow, it would be the celestial event of the year, perhaps even the century, leaving a cosmic imprint in the sky for all to see.

    In the night sky, the constellation Orion is most well-known for his belt, a row of three luminous stars.

    Orion Nebula M. Robberto NASA ESA Space Telescope Science Institute Hubble

    Orion Nebula ESO/VLT

    For the last few months, though, astronomers around the world have been particularly interested in his right shoulder, the home of a star called Betelgeuse, one of the brightest stars in the sky. Betelgeuse—which, yes, is pronounced like Beetlejuice—has been dimming more than it ever had before. Astronomers have long known that Betelgeuse is aging and, like many old stars, is bound to explode sooner or later. Could this mystery dimming mean that a supernova might be imminent?

    The view would be mind-boggling, day or night. The Orion constellation can be seen from nearly everywhere on Earth, which means nearly everyone could see the exploding star. It would easily cut through the artificial-light pollution that prevents 80 percent of the world—and a staggering 99 percent of the United States and Europe—from experiencing a clear view of the night sky.

    “At the predicted brightness of a Betelgeuse supernova, you could be standing in the center of the biggest city in the world, and you would certainly see it,” says John Barentine, an astronomer and the director of public policy at the International Dark-Sky Association, a nonprofit that works to mitigate light pollution. “You couldn’t miss it.”

    Even more spectacular, the display would stick around. The gleaming orb would remain visible for more than a year, perhaps even longer. How strange it would be to witness day in and day out, to understand, for the most part, that the blaze is simply a natural wonder of the universe, but still feel, on a deeper, more primitive level, that the sky looks very wrong.

    The supernova wouldn’t harm Earth. Betelgeuse isn’t the sort of star whose demise would produce radiation that could roil the planet’s atmosphere. At about 650 light-years from here, Betelgeuse is nearby on a cosmic scale, but thankfully not close enough to cause any damage.

    So how might people react? Judging by what happened in New York about a year ago, there would be confusion, even panic. One night in December, an aquamarine glow appeared over Queens, prompting 3,200 calls to 911 in half an hour. Residents shared videos and photos of the ghostly spectacle on social media, along with guesses for the source. Was this a bomb? Was it the climax of a ground-shaking battle between superheroes?

    The real explanation was far less dramatic. The operator of an electrical-power plant quickly chimed in on social media to describe the incident. Some equipment at the facility had short-circuited, and the malfunction sent a powerful current shooting into the air. The electricity jostled atoms of gas in the atmosphere, prompting them to emit blue light.

    A similar scenario would likely play out online in the case of a surprise supernova, with NASA and other science institutions leading the awareness campaign. “The way the world is on edge about a number of things right now, whether it’s climate change or international relations, it would be interesting how people would interpret it, if some people would think that it was some kind of sign,” Barentine says.

    The most recent nearby supernova appeared long before people could panic about it on Twitter, in 1987, but it could be seen only in very dark parts of the Southern Hemisphere, far from artificial lights. Other examples are found even deeper in history, in 1604 and 1054. Betelgeuse would provide a far better show; the other stars were thousands of light-years from Earth, rather than hundreds.

    The question is, of course, when. Scientists can’t predict Betelgeuse’s end because they have never witnessed the lead-up to a supernova, only the glowing aftermath, with the help of powerful telescopes. This is why astronomers have been saying Betelgeuse could go supernova “any day now” for years. The star might explode tomorrow or in 100,000 years, says Stella Kafka, an astronomer at the American Association of Variable Star Observers who studies Betelgeuse and similar twinkling stars. It’s even possible the supernova has already happened, and the light from the explosion is still making its way to Earth.

    On top of that, astronomers don’t have any proof that the mysterious dimming is a precursor to a supernova. Although Betelgeuse has never darkened this much, it’s known for periodic fluctuations in brightness, and there might be a nonexplosive explanation for the latest extreme dip, like nearby clouds of dust crowding out the light.

    “It would be interesting if the dimming is connected, but we don’t really know that,” Kafka says.

    While a Betelgeuse supernova would eventually fade, its mark on the planet would remain, and not just within the ether of the internet. When stars explode, they release a cascade of newly forged elements into space. These elements glide across the universe inside particles of dust, settling on whatever they encounter. Astronomers have detected this stardust all over Earth, inside mud on the ocean floor and snow in Antarctica. It is these explosions and the cosmic droplets they unleashed that helped give rise, over eons, to other stars, planets, and, in our case, life. Someday, a bunch of stardust might look up at the sky and see it happening all over again.

    See the full article here .

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  • richardmitnick 12:04 pm on August 15, 2019 Permalink | Reply
    Tags: , , , , , Supernovae, The idea of pair-instability supernovas has been around for decades, The supernova SN2016iet   

    From Harvard-Smithsonian Center for Astrophysics: “Scientists Observe the Explosion of a Monster Star Requiring New Supernova Mechanism” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    August 15, 2019
    Amy Oliver
    Public Affairs Officer
    Fred Lawrence Whipple Observatory
    Center for Astrophysics | Harvard & Smithsonian
    amy.oliver@cfa.harvard.edu
    +1 520-879-4406
    mobile: +1-801-783-9067

    CfA Whipple Observatory, located near Amado, Arizona on the slopes of Mount Hopkins, Altitude 2,606 m (8,550 ft)

    1
    Artist’s conception of the explosion of SN2016iet’s host star within a dense stellar environment. Credit: Joy Pollard/Gemini

    Scientists at the Center for Astrophysics | Harvard & Smithsonian have announced the discovery of the most massive star ever known to be destroyed by a supernova explosion, challenging known models of how massive stars die and providing insight into the death of the first stars in the universe.

    First noticed in November 2016 by the European Space Agency’s (ESA) Gaia satellite, three years of intensive follow up observations of the supernova SN2016iet revealed characteristics—incredibly long duration and large energy, unusual chemical fingerprints, and an environment poor in metals—for which there are no analogues in the existing astronomical literature.

    ESA/GAIA satellite

    “When we first realized how thoroughly unusual SN2016iet is my reaction was ‘whoa – did something go horribly wrong with our data?'” said Mr. Sebastian Gomez, Harvard University graduate student and lead author of the paper. “After a while we determined that SN2016iet is an incredible mystery, located in a previously uncatalogued galaxy one billion light years from Earth.”

    The team used a variety of telescopes, including the CfA | Harvard & Smithsonian’s MMT Observatory located at the Fred Lawrence Whipple Observatory in Amado, AZ, and the Magellan Telescopes at the Las Campanas Observatory in Chile to show that SN2016iet is different than the thousands of supernovas observed by scientists for decades.

    CfA U Arizona Fred Lawrence Whipple Observatory Steward Observatory MMT Telescope at the summit of Mount Hopkins near Tucson, Arizona, USA, Altitude 2,616 m (8,583 ft)

    Carnegie 6.5 meter Magellan Baade and Clay Telescopes located at Carnegie’s Las Campanas Observatory, Chile. over 2,500 m (8,200 ft) high

    “Everything about this supernova looks different—its change in brightness with time, its spectrum, the galaxy it is located in, and even where it’s located within its galaxy, said Dr. Edo Berger, Professor of Astronomy at Harvard University and an author on the paper. “We sometimes see supernovas that are unusual in one respect, but otherwise are normal; this one is unique in every possible way.”

    The observations and analysis show that SN2016iet began as an incredibly massive star 200 times the mass of Earth’s Sun that mysteriously formed in isolation roughly 54,000 light years from the center of its host dwarf galaxy. The star lost about 85 percent of its mass during a short life of only a few million years, all the way up to its final explosion and demise. The collision of the explosion-debris with the material shed in the final decade before explosion led to SN2016iet’s unusual appearance, providing scientists with the first strong case of a pair-instability supernova.

    “The idea of pair-instability supernovas has been around for decades,” said Berger. “But finally having the first observational example that puts a dying star in the right regime of mass, with the right behavior, and in a metal-poor dwarf galaxy is an incredible step forward. SN2016iet represents the way in which the most massive stars in the universe, including the first stars, die.”

    The team will continue to observe and study SN2016iet for years, watching for additional clues as to how it formed, and how it will evolve. “Most supernovas fade away and become invisible against the glare of their host galaxies within a few months. But because SN2016iet is so bright and so isolated we can study its evolution for years to come,” said Gomez. “These observations are already in progress and we can’t wait to see what other surprises this supernova has in store for us.”

    The results of the study are published in The Astrophysical Journal. In addition to Gomez and Berger, the study involved scientists from CfA | Harvard & Smithsonian—Peter K. Blanchard, V. Ashley Villar, Locke Patton, Joel Leja, and Griffin Hosseinzadeh; along with scientists from the University of Edinburgh—Matt Nicholl; Ohio University—Ryan Chornock; and, The Observatories of the Carnegie Institution for Science—Philip S. Cowperthwaite.

    See the full article here .


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    Please help promote STEM in your local schools.

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    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 10:24 am on July 18, 2019 Permalink | Reply
    Tags: "Exploring an Odd Stellar Death", , , , , , Supernovae   

    From AAS NOVA: “Exploring an Odd Stellar Death” 

    AASNOVA

    From AAS NOVA

    17 July 2019
    Susanna Kohler

    1
    Artist’s impression of a supernova explosion. A new study explores whether the merger of two massive stars could lead to a unique kind of supernova. [ESO/M. Kornmesser]

    Massive stars can die in a lot of different ways! A new study explores one possible channel in more detail.

    Detectives Are on the Case

    2
    Artist’s illustration of a star exploding in a supernova at the end of its lifetime. [NASA/CXC/M. Weiss]

    NASA/Chandra X-ray Telescope

    Studying supernovae is a little like being a detective in an odd sort of murder mystery. You’ve witnessed the death of a massive star — and from this evidence, you must determine what type of star died, how it died, and even what interactions it had before its death.

    As we enter the era of ever more expansive sky surveys, we can expect to amass not just evidence of typical stellar deaths, but also some more unusual ones. In the process, piecing together the evidence to solve each mystery becomes progressively more challenging — but also more intriguing!

    In a recent study, a team of scientists led by Alejandro Vigna-Gómez (U. of Birmingham, UK; Monash U., Australia; U. of Copenhagen, Denmark) have explored one particular oddball type of theorized stellar death: pulsational pair-instability supernovae (PISNe).

    Gravity (Usually) Wins

    According to theory, PISNe occur when a very massive (hundreds of solar masses) star gets hot enough to start producing pairs of electrons and positions. This process saps the star’s internal energy, leading to its sudden collapse as the force of gravity triumphs.

    This collapse can end in the dramatic explosion of a PISN, or it may lead to a smaller eruption that only sheds some of the star’s mass. In the latter case, the star may go through multiple rounds of smaller eruptions before eventually running out of nuclear fuel and undergoing a final explosion — as a pulsational PISN.

    3
    Schematic showing three possible ways massive stars can die; click to enlarge. Top and bottom panels describe outcomes of single-star evolution, depending on the star’s mass. The center channel depicts the merger of two evolved, massive stars to form an object with a large envelope of hydrogen. This can lead to a hydrogen-rich pulsational PISN. [Vigna-Gómez et al. 2019]

    Starting with a Merger

    If this weren’t complicated enough, Vigna-Gómez and collaborators propose one further twist on this stellar death scenario: the object exploding in a pulsational PISN needn’t simply be a massive star. Instead, it might be the product of the merger of two massive stars.

    Vigna-Gómez and collaborators argue that this type of merger is expected to be common, and it would produce a very massive object with a large outer hydrogen shell. By running a series of simulations using the Modules for Experiments in Stellar Astrophysics (MESA), the authors demonstrate that such a merger product could undergo a pulsational PISN and still retain a significant portion of its hydrogen shell up to the final explosion, leaving the fingerprint of hydrogen in the supernova spectrum.

    4
    The light curve of iPTF14hls is extremely unusual, featuring multiple apparent explosions. [Adapted from Las Cumbres Observatory/S. Wilkinson]

    LCO_map_2017. Map of the Las Cumbres Observatory global network of robotic telescopes

    Explanation for a Zombie Star?

    Why does this particular theorized death matter? Stellar detectives are currently working to explain the deaths in a number of especially weird observed supernovae, and this model might match some of them. One example is iPTF14hls, the “zombie star” that’s made headlines for apparently erupting multiple times and defying explanation — in part because of the unexpected hydrogen signatures in its spectra.

    We can’t yet say for sure whether iPTF14hls is an example of a stellar-merger-turned-pulsational-PISN — that will require more extensive modeling and analysis of observations — but Vigna-Gómez and collaborators think it’s a good candidate! And while we wait on the verdict of that mystery, we can be sure that transient surveys are busy finding many more examples of stellar deaths for us to puzzle over.

    Citation

    “Massive Stellar Mergers as Precursors of Hydrogen-rich Pulsational Pair Instability Supernovae,” Alejandro Vigna-Gómez et al 2019 ApJL 876 L29.
    https://iopscience.iop.org/article/10.3847/2041-8213/ab1bdf

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 8:16 am on June 25, 2019 Permalink | Reply
    Tags: "The highest-energy photons ever seen hail from the Crab Nebula", , , , , , , , Supernovae, The Tibet AS-gamma experiment, When a high-energy photon hits Earth’s atmosphere it creates a shower of other subatomic particles that can be detected on the ground.   

    From Science News: “The highest-energy photons ever seen hail from the Crab Nebula” 

    From Science News

    June 24, 2019
    Emily Conover

    Some of the supernova remnant’s gamma rays have more than 100 trillion electron volts of energy.

    1
    CRAB FISHING Scientists hunting for high-energy photons raining down on Earth from space have found the most energetic light yet detected. It’s from the Crab Nebula, a remnant of an exploded star (shown in an image combining light seen by multiple telescopes).

    Physicists have spotted the highest-energy light ever seen. It emanated from the roiling remains left behind when a star exploded.

    This light made its way to Earth from the Crab Nebula, a remnant of a stellar explosion, or supernova, about 6,500 light-years away in the Milky Way. The Tibet AS-gamma experiment caught multiple particles of light — or photons — from the nebula with energies higher than 100 trillion electron volts, researchers report in a study accepted in Physical Review Letters. Visible light, for comparison, has just a few electron volts of energy.

    Tibet AS Gamma Expeiment

    “This energy regime has not been accessible before,” says astrophysicist Petra Huentemeyer of Michigan Technological University in Houghton, who was not involved with the research. For physicists who study this high-energy light, known as gamma rays, “it’s an exciting time,” she says.

    In space, supernova remnants and other cosmic accelerators can boost subatomic particles such as electrons, photons and protons to extreme energies, much higher than those achieved in the most powerful earthly particle accelerators (SN: 10/1/05, p. 213). Protons in the Large Hadron Collider in Geneva, for example, reach a comparatively wimpy 6.5 trillion electron volts. Somehow, the cosmic accelerators vastly outperform humankind’s most advanced machines.

    “The question is: How does nature do it?” says physicist David Hanna of McGill University in Montreal.

    In the Crab Nebula, the initial explosion set up the conditions for acceleration, with magnetic fields and shock waves plowing through space, giving an energy boost to charged particles such as electrons. Low-energy photons in the vicinity get kicked to high energies when they collide with the speedy electrons, and ultimately, some of those photons make their way to Earth.

    When a high-energy photon hits Earth’s atmosphere, it creates a shower of other subatomic particles that can be detected on the ground. To capture that resulting deluge, Tibet AS-gamma uses nearly 600 particle detectors spread across an area of more than 65,000 square meters in Tibet. From the information recorded by the detectors, researchers can calculate the energy of the initial photon.

    But other kinds of spacefaring particles known as cosmic rays create particle showers that are much more plentiful. To select photons, cosmic rays, which are mainly composed of protons and atomic nuclei, need to be weeded out. So the researchers used underground detectors to look for muons — heavier relatives of electrons that are created in cosmic ray showers, but not in showers created by photons.

    Previous experiments have glimpsed photons with nearly 100 TeV, or trillion electron volts. Now, after about three years of gathering data, the researchers found 24 seemingly photon-initiated showers above 100 TeV, and some with energies as high as 450 TeV. Because the weeding out process isn’t perfect, the researchers estimate that around six of those showers could have come from cosmic rays mimicking photons, but the rest are the real deal.

    Researchers with Tibet AS-gamma declined to comment for this story, as the study has not yet been published.

    Looking for photons of ever higher energies could help scientists nail down the details of how the particles are accelerated. “There has to be a limit to how high the energy of the photons can go,” Hanna says. If scientists can pinpoint that maximum energy, that could help distinguish between various theoretical tweaks to how the particles get their oomph.

    See the full article here .


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    Please help promote STEM in your local schools.

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