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  • richardmitnick 10:35 am on April 21, 2017 Permalink | Reply
    Tags: , , Supernovae,   

    From COSMOS: “Sixteen ways of looking at a supernova” 

    Cosmos Magazine bloc

    COSMOS

    21 April 2017
    Andrew Masterson

    Thanks to fast thinking, luck, and gravitational lensing, four telescopes managed to observe a quadruple image of a single supernova. Andrew Masterson reports.

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    The light from the supernova iPTF16geu and of its host galaxy is warped and amplified by the curvature of space by the mass of a foreground galaxy.
    ALMA (ESO/NRAO/NAOJ), L. Calçada (ESO), Y. Hezaveh et al., edited and modified by Joel Johansson

    In September 2016, when astronomer Ariel Goobar and his colleagues at the Intermediate Palomar Transient Factory in California saw the image recorded by the facility’s field camera, they knew they had to move fast.

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

    They were looking at something that was simultaneously massive, spectacular, new, short-lived, and a triumphant demonstration of Einstein’s theory of general relativity.

    As reported in the journal Science, Goobar, from Stockholm University in Sweden, and his team had discovered a brand new Type 1a supernova, which they later dubbed iPTF16geu.

    Any freshly discovered supernova is a significant astronomical find, but in this case its importance was magnified – quite literally – by circumstance.

    Einstein’s theory of general relativity predicts that matter curves the spacetime surrounding it. The region of curved spacetime around a particularly massive object – a galaxy, say – can, if the alignment is correct, bend the paths of light travelling through it in such a way as to act as a lens, enlarging the appearance of objects in the distance behind it.

    The effect is known as “gravitational lensing” and is well known to astronomers.

    Gravitational Lensing NASA/ESA

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    From left: an image from the SDSS survey; a zoomed view showing the foreground lensing galaxy; two versions of the four resolved images of the supernova, resolved by the Hubble Space Telescope and the Keck/NIRC2 instrument. Joel Johansson

    Goobar’s team quickly realised that its view of iPTF16geu was an extreme example of the phenomenon. A galaxy situated between Earth and the supernova was magnifying the phenomenon by 50 times, providing an unparalleled view of the stellar explosion. They were also able to see four separate images of the supernova, each formed by light taking a different path around the galaxy.

    The light burst from a Type 1 supernova starts to fade precipitously after only a couple of minutes, and disappears pretty much completely after a year.

    Realising that the window of opportunity was limited and closing fast, the team hit the phones and did some rapid talking. In a very short period, three other big facilities homed in on iPTF16geu.

    As well as the initial Palomar shot, the astronomers captured images from the Hubble Telescope, the Very Large Telescope in Chile, and the Keck Observatory in Hawaii.

    NASA/ESA Hubble Telescope

    ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    Keck Observatory, Mauna Kea, Hawaii, USA

    The results – multiple observations of multiple images of the supernova event – provide data that will offer insights not only into the supernova itself, but also into the structure of the intervening galaxy and the physics of gravitational lensing.

    See the full article here .

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  • richardmitnick 12:58 pm on March 30, 2017 Permalink | Reply
    Tags: , , , , , , Supernovae   

    From Hubble: “Search For Stellar Survivor of a Supernova Explosion ” Hubble-Europe and USA/HubbleSite 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope

    NASA/ESA Hubble Telescope

    You-Hua Chu
    Institute of Astronomy and Astrophysics, Academia Sinica
    Taipei, Taiwan
    Tel: +886 2 2366 5300
    Email: yhchu@asiaa.sincia.edu.tw

    Mathias Jäger
    ESA/Hubble, Public Information Officer
    Garching bei München, Germany
    Tel: +49 176 62397500
    Email: mjaeger@partner.eso.org

    Christine Pulliam
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-6437
    cpulliam@stsci.edu

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4514
    villard@stsci.edu

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    A group of astronomers used Hubble to study the remnant of the Type Ia supernova explosion SNR 0509-68.7 — also known as N103B (seen at the top). The supernova remnant is located in the Large Magellanic Cloud, just over 160 000 light-years from Earth.

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    This ground-based image shows both the Small and the Large Magellanic Clouds — two satellite galaxies of the Milky Way. The Small Magellanic Cloud can be seen on the left, the Large Magellanic Cloud on the right. This photo was taken by the Japanese astrophotographer Akira Fujii.

    In contrast to many other Supernova remnants N103B does not appear to have a spherical shape but is strongly elliptical. Astronomers assume that part of material ejected by the explosion hit a denser cloud of interstellar material, which slowed its speed. The shell of expanding material being open to one side supports this idea.

    The relative proximity of N103B allows astronomers to study the life cycles of stars in another galaxy in great detail. And probably even to lift the veil on questions surrounding this type of supernova. The predictable luminosity of Type Ia supernovae means that astronomers can use them as cosmic standard candles to measure their distances, making them useful tools in studying the cosmos. Their exact nature, however, is still a matter of debate. Astronomers suspect Type Ia supernovae occur in binary systems in which at least one of the stars in the pair is a white dwarf [1].

    There are currently two main theories describing how these binary systems become supernovae. Studies like the one that has provided the new image of N103B — that involve searching for remnants of past explosions — can help astronomers to finally confirm one of the two theories.

    One theory assumes that both stars in the binary are white dwarfs. If the stars merge with one another it would ultimately lead to a supernova explosion of type Ia.

    The second theory proposes that only one star in the system is a white dwarf, while its companion is a normal star. In this theory material from the companion star is accreted onto the white dwarf until its mass reaches a limit, leading to a dramatic explosion. In that scenario, the theory indicates that the normal star should survive the blast in at least some form. However, to date no residual companion around any type Ia supernova has been found.

    Astronomers observed the N103B supernova remnant in a search for such a companion. They looked at the region in H-alpha — which highlights regions of gas ionised by the radiation from nearby stars — to locate supernova shock fronts. They hoped to find a star near the centre of the explosion which is indicated by the curved shock fronts. The discovery of a surviving companion would put an end to the ongoing discussion about the origin of type Ia supernova.

    And indeed they found one candidate star that meets the criteria — for star type, temperature, luminosity and distance from the centre of the original supernova explosion. This star has approximately the same mass as the Sun, but it is surrounded by an envelope of hot material that was likely ejected from the pre-supernova system.

    Although this star is a reasonable contender for N103B’s surviving companion, its status cannot be confirmed yet without further investigation and a spectroscopic confirmation. The search is still ongoing.

    Notes

    [1] A white dwarf is the small, dense core of a medium-mass star that is left behind after it has reached the end of its main-sequence lifetime and blown off its outer layers. Our own Sun is expected to become a white dwarf in around five billion years.

    See the full article here .

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

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  • richardmitnick 10:54 am on March 22, 2017 Permalink | Reply
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    From Ethan Siegel: “What Will Happen When Betelgeuse Explodes?” 

    Ethan Siegel
    Mar 22, 2017

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    The constellation of Orion, along with the great molecular cloud complex and including its brightest stars. Betelgeuse, the nearby, bright red supergiant (and supernova candidate), is at the lower left. Rogelio Bernal Andreo

    Every star will someday run out of fuel in its core, bringing an end to its run as natural source of nuclear fusion in the Universe. While stars like our Sun will fuse hydrogen into helium and then — swelling into a red giant — helium into carbon, there are other, more massive stars which can achieve hot enough temperatures to further fuse carbon into even heavier elements. Under those intense conditions, the star will swell into a red supergiant, destined for an eventual supernova after around 100,000 years or so. And the brightest red supergiant in our entire night sky? That’s Betelgeuse, which could go supernova at any time.

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    The color-magnitude diagram of notable stars. The brightest red supergiant, Betelgeuse, is shown at the upper right. European Southern Observatory.

    Honestly, at its distance of 640 light years from us, it could have gone supernova at any time from the 14th century onwards, and we still wouldn’t know. Betelgeuse is one of the ten brightest stars in the sky in visible light, but only 13% of its energy output is detectable to human eyes. If we could see the entire electromagnetic spectrum — including into the infrared — Betelgeuse would, from our perspective, outshine every other star in the Universe except our Sun.

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    Three of the major stars in Orion — Betelgeuse, Meissa and Bellatrix — as revealed in the infrared. In IR light, Betelgeuse (lower left) is the brightest star in the night sky. NASA / WISE.

    It was the first star ever to be resolved as more than a point source. At 900 times the size of our Sun, it would engulf Mercury, Venus, Earth, Mars and even the asteroid belt if it were to replace our parent star. It’s a pulsating star, so its diameter changes with time.

    In addition, it’s constantly losing mass, as the intense fusion reactions begin to expel the outermost, tenuously-held layers. Direct radio observations can actually detect this blown-off matter, and have found that it extends to beyond the equivalent of Neptune’s orbit.

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    The nebula of expelled matter created around Betelgeuse, which, for scale, is shown in the interior red circle. This structure, resembling flames emanating from the star, forms because the behemoth is shedding its material into space. ESO/P. Kervella

    But when we study the night sky, we’re studying the past. We know that Betelgeuse, with an uncertain mass between about 12 and 20 times that of our Sun, was never destined to live very long: maybe around 10 million years only. The more massive a star is, the faster it burns through its fuel, and Betelgeuse is burning so very, very brightly: at around 100,000 times the luminosity of our Sun. It’s currently in the final stages of its life — as a red supergiant — meaning that when the innermost core begins fusing silicon and sulphur into iron, nickel and cobalt, the star itself will only have minutes left.

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    The anatomy of a very massive star throughout its life, culminating in a Type II Supernova. Nicole Rager Fuller for the NSF.

    At those final moments, the core will be incredibly hot, yet iron, nickel and cobalt will be unable to fuse into anything heavier. It’s energetically unfavorable to do so, and so no new radiation will be produced in the innermost regions. Yet gravitation is still at play, trying to pull the star’s core in on itself. Without nuclear fusion to hold it up, the core has no other options, and begins to implode. The contraction causes it to heat up, become denser, and achieve pressures like it’s never seen before. And once a critical junction has passed, it happens: the atomic nuclei in the star’s core begin a runaway fusion reaction all at once.

    This is what creates a Type II supernova: the core-collapse of an ultra-massive star. After a brief, initial flash, Betelgeuse will brighten tremendously over a period of weeks, rising to a maximum brightness that, intrinsically, will be billions of times as bright as the Sun. It will remain at maximum brightness for months, as radioactive cobalt and expanding gases cause a continuous bright emission of light.

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    At peak brightness, a supernova can shine nearly as brightly as the rest of the stars in a galaxy combined. This 1994 image shows a typical example of a core-collapse supernova relative to its host galaxy. NASA/ESA, The Hubble Key Project Team and The High-Z Supernova Search Team

    Supernovae have occurred in our Milky Way in the past: in 1604, 1572, 1054 and 1006, among others, with a number of them being so bright that they were visible during the day. But none of them were as close at Betelgeuse.

    At only 600-or-so light years distant, Betelgeuse will be far closer than any supernova ever recorded by humanity. It’s fortunately still far away enough that it poses no danger to us. Our planet’s magnetic field will easily deflect any energetic particles that happen to come our way, and it’s distant enough that the high-energy radiation reaching us will be so low-density that it will have less of an impact on you than the banana you had at breakfast. But oh, will it ever appear bright.

    Not only will Betelgeuse be visible during the day, but it will rival the Moon for the second-brightest object in the sky. Some models “only” have Betelgeuse getting as bright as a thick crescent moon, while others will see it rival the entire full moon. It will conceivably be the brightest object in the night sky for more than a year, until it finally fades away to a dimmer state.

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    The ultra-massive star Wolf-Rayet 124, shown with its surrounding nebula, is one of thousands of Milky Way stars that could be our galaxy’s next supernova. Betelgeuse is merely the closest known potential candidate. Hubble Legacy Archive / A. Moffat / Judy Schmidy

    Unfortunately, the key question of “when” is not one we have an answer to; thousands of other stars in the Milky Way may go supernova before Betelgeuse does. Until we develop an ultra-powerful neutrino telescope to measure the energy spectrum of neutrinos being generated by (and hence, which elements are being fused inside) a star like Betelgeuse, hundreds of light years away, we won’t know how close it is to going supernova. It could have exploded already, with the light from the cataclysm already on its way towards us… or it could remain no different than it appears today for another hundred thousand years.

    See the full article here .

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

     
  • richardmitnick 3:07 pm on March 15, 2017 Permalink | Reply
    Tags: ASCR Discovery, Coding a Starkiller, DOE, , Supernovae   

    From OLCF via ASCR and DOE: “Coding a Starkiller” 

    i1

    Oak Ridge National Laboratory

    OLCF

    ASCR

    March 2017

    The Titan supercomputer and a tool called Starkiller help Stony Brook University-led team simulate key moments in exploding stars.

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    A volume rendering of the density after 0.6 and 0.9 solar mass white dwarfs merge. The image is derived from a calculation performed on the Oak Ridge Leadership Computing facility’s Titan supercomputer. The model used Castro, an adaptive mesh astrophysical radiation hydrodynamics simulation code. Image courtesy of Stony Brook University / Max Katz et al.

    The spectacular Supernova 1987A, whose light reached Earth on Feb. 23 of the year it’s named for, captured the public’s fancy. It’s located at the edge of the Milky Way, in a dwarf galaxy called the Large Magellanic Cloud. It had been four centuries since earthlings had witnessed light from a star exploding in our galaxy.

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    NASA

    A supernova’s awesome light show heralds a giant star’s death, and the next supernova’s post-mortem will generate reams of data, compared to the paltry dozen or so neutrinos and X-rays harvested from the 1987 event.

    Astrophysicists Michael Zingale and Bronson Messer aren’t waiting. They’re aggressively anticipating the next supernova by leading teams in high-performance computer simulations of explosive stellar events, including different supernova types and their accompanying X-ray bursts. Zingale, of Stony Brook University, and Messer, of the Department of Energy’s Oak Ridge National Laboratory (ORNL), are in the midst of an award from the DOE Office of Science’s Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program. It provides an allocation of 45 million processor hours of computer time on Titan, a Cray XK7 that’s one of the world’s most powerful supercomputers, at the Oak Ridge Leadership Computing Facility, or OLCF – a DOE Office of Science user facility.

    The simulations run on workhorse codes developed by the INCITE collaborators and at the DOE’s Lawrence Berkeley National Laboratory – codes that “are often modified toward specific problems,” Zingale says. “And the common problem we share with ORNL is that we have to put more and more of our algorithms on the Titan graphics processor units (GPUs),” specialized computer chips that accelerate calculations. While the phenomena they’re modeling “are really far away and on scales that are hard to imagine,” the codes have other applications closer to home: “terrestrial phenomena, like terrestrial combustion.” The team’s codes – Maestro, Castro, Chimera and FLASH – are available to other modelers free through online code repository Github.

    With a previous INCITE award, the researchers realized the possibility of attacking the GPU problem together. They envisioned codes comprised of multiphysics modules that compute common pieces of most kinds of explosive activities, Messer says. They dubbed the growing collection of GPU-enabled modules Starkiller.

    “Starkiller ties this INCITE project together,” he says. “We realized we didn’t want to reinvent the wheel with each new simulation.” For example, a module that tracks nuclear burning helps the researchers create larger networks for nucleosynthesis, a supernova process in which elements form in the turbulent flow on the stellar surface.

    “In the past, we were able to do only a little more than a dozen different elements, and now we’re routinely doing 150,” Messer says. “We can make the GPU run so much faster. That’s part of Titan’s advantage to us.”

    Supernova 1987A, a type II supernova, arose from the gravitational collapse of a stellar core, the consistent fate of massive stars. Type Ia supernovae follow from intense thermonuclear activities that eventually drive the explosion of a white dwarf – a star that has used up all its hydrogen. Zingale’s group is focused on type Ia, Messer’s on type II. A type II leaves a remnant star; a type Ia does not.

    Stars like the sun burn hydrogen into helium and, over enormous stretches of time, burn the helium into carbon. Once our sun starts burning carbon, it will gradually peter out, Messer says, because it’s not massive enough to turn the carbon into something heavier.

    “A star begins life as a big ball of hydrogen, and its whole life is this fight between gravity trying to suck it into the middle and thermonuclear reactions keeping it supported against its own gravity,” he adds. “Once it gets to the point where it’s burning some carbon, the sun will just give up. It will blow a big smoke ring into space and become a planetary nebula, and at the center it will become a white dwarf.”

    Zingale is modeling two distinct thermonuclear modes. One is for a white dwarf in a binary system – two stars orbiting one another – that consumes additional material from its partner. As the white dwarf grows in mass, it gets hotter and denser in the center, creating conditions that drive thermonuclear reactions.

    “This star is made mostly of carbon and oxygen,” Zingale says. “When you get up to a few hundred million K, you have densities of a few billion grams per cubic centimeter. Carbon nuclei get fused and make things like neon and sodium and magnesium, and the star gets energy out in that process. We are modeling the star’s convection, the creation of a rippling burning front that converts the carbon and oxygen into heavier elements such as iron and nickel. This creates such an enormous amount of energy that it overcomes the force of gravity that’s holding the star together, and the whole thing blows apart.”

    The other mode is being modeled with former Stony Brook graduate student and INCITE co-principal investigator Max Katz, who want to understand whether merging stars can create a burning point that leads to a supernova, as some observations suggest. His simulations feature two white dwarfs so close that they emit gravitational radiation, robbing energy from the system and causing the stars to spiral inward. Eventually, they get so close that the more massive one rips the lesser apart via tidal energy.

    Zingale’s group also continues to model the convective burning on stars, known as X-ray bursts, providing a springboard to more in-depth studies. He says they’re the first to simulate them in three dimensions. That work and additional supernova studies were supported by the DOE Office of Science and performed at OLCF and the National Energy Research Scientific Computing Center, a DOE Office of Science user facility at Lawrence Berkeley National Laboratory.

    See the full article here .

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

    i2

    The Oak Ridge Leadership Computing Facility (OLCF) was established at Oak Ridge National Laboratory in 2004 with the mission of accelerating scientific discovery and engineering progress by providing outstanding computing and data management resources to high-priority research and development projects.

    ORNL’s supercomputing program has grown from humble beginnings to deliver some of the most powerful systems in the world. On the way, it has helped researchers deliver practical breakthroughs and new scientific knowledge in climate, materials, nuclear science, and a wide range of other disciplines.

    The OLCF delivered on that original promise in 2008, when its Cray XT “Jaguar” system ran the first scientific applications to exceed 1,000 trillion calculations a second (1 petaflop). Since then, the OLCF has continued to expand the limits of computing power, unveiling Titan in 2013, which is capable of 27 petaflops.


    ORNL Cray XK7 Titan Supercomputer

    Titan is one of the first hybrid architecture systems—a combination of graphics processing units (GPUs), and the more conventional central processing units (CPUs) that have served as number crunchers in computers for decades. The parallel structure of GPUs makes them uniquely suited to process an enormous number of simple computations quickly, while CPUs are capable of tackling more sophisticated computational algorithms. The complimentary combination of CPUs and GPUs allow Titan to reach its peak performance.

    The OLCF gives the world’s most advanced computational researchers an opportunity to tackle problems that would be unthinkable on other systems. The facility welcomes investigators from universities, government agencies, and industry who are prepared to perform breakthrough research in climate, materials, alternative energy sources and energy storage, chemistry, nuclear physics, astrophysics, quantum mechanics, and the gamut of scientific inquiry. Because it is a unique resource, the OLCF focuses on the most ambitious research projects—projects that provide important new knowledge or enable important new technologies.

     
  • richardmitnick 2:23 pm on March 15, 2017 Permalink | Reply
    Tags: , , , , , Supernovae   

    From Astronomy: “There’s a supernova occurring right now in NGC 5643” 

    Astronomy magazine

    astronomy.com

    March 15, 2017
    Alison Klesman

    Meet “Bob,” the second Type Ia supernova in the galaxy since 2013

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    Racheal Beaton / Carnegie Institution for Science

    When most people hear the word supernova, they envision a massive star reaching the end of its life and exploding outwards to leave a ghostly remnant in its place. This is called a Type II supernova — the spectacular Supernova 1987A, which recently celebrated its 30th anniversary, was a Type II.

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    Supernova 1987A NASA

    Alternatively, a Type Ia supernova occurs when a white dwarf, the remnant of a Sun-like star, grows too massive after stripping a binary companion star of its outer layers. When the white dwarf reaches a critical mass, a runaway fusion reaction occurs in its core and the star explodes in a Type Ia supernova. Such a supernova has just been spotted occurring in a galaxy about 55 million light-years away.

    Announced by Rachael Beaton at the the Observatories of the Carnegie Institution for Science in Pasadena, CA, and known as 2017cbv (though Beaton has nicknamed it Bob), the explosion was spotted in NGC 5643, a spiral galaxy in the constellation Lupus. The area of the sky it inhabits is also part of the area covered by the Carnegie-Irvine Galaxy Survey, a project aimed at gathering optical and near-infrared images of bright Southern Hemisphere galaxies. NGC 5643 was also the home galaxy of SN 2013aa, which occurred in early 2013.

    Type Ia supernovae play an extremely important role as rungs on the astronomical distance ladder that allows astronomers to measure the distance to faraway galaxies. They’ve also played a critical role in measuring the accelerating expansion of the universe. Because they occur in white dwarfs of exactly the same mass every time (that critical mass mentioned earlier: about 1.4 times the mass of the Sun), Type Ia supernovae are always the same brightness, which means astronomers can use them as standard candles. Knowing how bright the explosion is in terms of absolute luminosity allows astronomers to then work backwards to calculate the distance to the object based on how bright it appears.

    But the word “exactly” is perhaps a bit misleading. Not every star system in which a Type Ia supernova occurs can be exactly the same. Moreover, events in the real world do not always reflect the precise nature of theoretical calculations — as in, some white dwarfs might explode at a mass slightly under 1.4 solar masses, while others might grow a little heavier than this limit before exploding. The fact that 2017cbv is the second recorded Type Ia supernova to occur in NGC 5643 is thus extremely valuable. By comparing the distance to the galaxy as calculated from each supernova, astronomers can better characterize the real-world variance in supernova Type Ia magnitudes that occur, which in turn will improve the accuracy of using these events to measure distance.

    See the full article here .

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  • richardmitnick 11:37 am on March 14, 2017 Permalink | Reply
    Tags: , , , , Supernovae,   

    From Weizmann: “Explosive Material: The Making of a Supernova” 

    Weizmann Institute of Science logo

    Weizmann Institute of Science

    Pre-supernova stars may show signs of instability for months before the big explosion

    14.03.2017

    In the most common type of supernova, the iron core of a massive star suddenly collapses in on itself and the outer layers are thrown out into space in a spectacular explosion. New research led by Weizmann Institute of Science researchers shows that the stars that become so-called core-collapse supernovae might already exhibit instability for several months before the big event, spewing material into space and creating a dense gas shell around themselves. They think that many massive stars, including the red super-giants that are the most common progenitors of these supernovae, may begin the process this way.

    This insight into the conditions leading up to core collapse arose from a unique collaboration called the Palomar Transient Factory, a fully automated sky survey using the telescopes of the Palomar observatory in southern California.


    Palomar Transient Factory, located in San Diego County, California

    Astrophysicists halfway around the globe, in Israel, are on call for the telescope, which scans the California night sky for the sudden appearance of new astronomical “transients” that were not visible before – which can indicate new supernovae. In October, 2013, Dr. Ofer Yaron, in the Weizmann Institute’s Particle Physics and Astrophysics Department, got the message that a potential supernova had been sighted, and he immediately alerted Dr. Dan Perley who was observing that night with the Keck telescope in Hawaii, and NASA’s Swift Satellite.


    Keck Observatory, Mauna Kea, Hawaii, USA


    NASA/SWIFT Telescope

    At Keck, the researchers soon began to record the spectra of the event. Because they had started observing only three hours into the blast, the picture the team managed to assemble was the most detailed ever of the core collapse process. “We had x-rays, ultraviolet, four spectroscopic measurements from between six and ten hours post-explosion to work with,” says Yaron.

    In the most common type of supernova, the iron core of a massive star suddenly collapses in on itself and the outer layers are thrown out into space in a spectacular explosion. New research led by Weizmann Institute of Science researchers shows that the stars that become so-called core-collapse supernovae might already exhibit instability for several months before the big event, spewing material into space and creating a dense gas shell around themselves. They think that many massive stars, including the red super-giants that are the most common progenitors of these supernovae, may begin the process this way.

    This insight into the conditions leading up to core collapse arose from a unique collaboration called the Palomar Transient Factory, a fully automated sky survey using the telescopes of the Palomar observatory in southern California. Astrophysicists halfway around the globe, in Israel, are on call for the telescope, which scans the California night sky for the sudden appearance of new astronomical “transients” that were not visible before – which can indicate new supernovae. In October, 2013, Dr. Ofer Yaron, in the Weizmann Institute’s Particle Physics and Astrophysics Department, got the message that a potential supernova had been sighted, and he immediately alerted Dr. Dan Perley who was observing that night with the Keck telescope in Hawaii, and NASA’s Swift Satellite. At Keck, the researchers soon began to record the spectra of the event. Because they had started observing only three hours into the blast, the picture the team managed to assemble was the most detailed ever of the core collapse process. “We had x-rays, ultraviolet, four spectroscopic measurements from between six and ten hours post-explosion to work with,” says Yaron.

    In a study recently published in Nature Physics, Yaron, Weizmann Institute researchers Profs. Avishay Gal-Yam and Eran Ofek, and their teams, together with researchers from the California Institute of Technology and other institutes in the United States, Denmark, Sweden, Ireland, Israel and the UK, analyzed the unique dataset they had collected from the very first days of the supernova.

    The time window was crucial: It enabled the team to detect material that had surrounded the star pre- explosion, as it heated up and became ionized and was eventually overtaken by the expanding cloud of stellar matter. Comparing the observed early spectra and light-curve data with existing models, accompanied by later radio observations, led the researchers to conclude that the explosion was preceded by a period of instability lasting for around a year. This instability caused material to be expelled from the surface layers of the star, forming the circumstellar shell of gas that was observed in the data. Because this was found to be a relatively standard type II supernova, the researchers believe that the instability they revealed may be a regular warm up act to the immanent explosion.

    “We still don’t really understand the process by which a star explodes as a supernova,” says Yaron, “These findings are raising new questions, for example, about the final trigger that tips the star from merely unstable to explosive. With our globe-spanning collaboration that enables us to alert various telescopes to train their sights on the event, we are getting closer and closer to understanding what happens in that instant, how massive stars end their life and what leads up to the final explosion.”

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    Prof. Avishay Gal-Yam’s research is supported by the Benoziyo Endowment Fund for the Advancement of Science; the Yeda-Sela Center for Basic Research; the Deloro Institute for Advanced Research in Space and Optics; and Paul and Tina Gardner. Prof. Gal-Yam is the recipient of the Helen and Martin Kimmel Award for Innovative Investigation.

    Dr. Eran Ofek’s research is supported by the Helen Kimmel Center for Planetary Science; Paul and Tina Gardner, Austin, TX; Ilan Gluzman, Secaucus, NJ; and the estate of Raymond Lapon.

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    Weizmann Institute Campus

    The Weizmann Institute of Science is one of the world’s leading multidisciplinary research institutions. Hundreds of scientists, laboratory technicians and research students working on its lushly landscaped campus embark daily on fascinating journeys into the unknown, seeking to improve our understanding of nature and our place within it.

    Guiding these scientists is the spirit of inquiry so characteristic of the human race. It is this spirit that propelled humans upward along the evolutionary ladder, helping them reach their utmost heights. It prompted humankind to pursue agriculture, learn to build lodgings, invent writing, harness electricity to power emerging technologies, observe distant galaxies, design drugs to combat various diseases, develop new materials and decipher the genetic code embedded in all the plants and animals on Earth.

    The quest to maintain this increasing momentum compels Weizmann Institute scientists to seek out places that have not yet been reached by the human mind. What awaits us in these places? No one has the answer to this question. But one thing is certain – the journey fired by curiosity will lead onward to a better future.

     
  • richardmitnick 1:57 pm on March 10, 2017 Permalink | Reply
    Tags: , , , , , Supernovae   

    From CfA: “Superluminous Supernovae” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    March 10, 2017

    1
    Wikipedia

    Supernovae, the explosive deaths of massive stars, are among the most momentous events in the cosmos because they disburse into space all of the chemical elements that were produced inside their progenitor stars, including the elements essential for making planets and life. Their bright emission also enables them to be used as probes of the very distant universe. Not least, supernovae are astrophysical laboratories for the study of very energetic phenomena. One class of supernovae consists of single stars whose mass is at least eight solar masses as they finish their lives.

    A typical supernova shines about as brightly as ten billion Suns at its peak. In the last decade, a new type of supernova was discovered that is ten to one hundred times more luminous than a normal massive stellar collapse supernova, and today over a dozen of these superluminous supernovae (SLSN) have been seen. Astronomers are in agreement that these objects come from the collapse of massive stars, but their tremendous luminosities cannot be explained by the usual physical mechanisms invoked. Instead, the debate has centered on whether the excess emission results from an external source, for example the interaction of material ejected from the explosion with a circumstellar shell, or instead by some kind of powerful internal engine such as a highly magnetized, spinning neutron star.

    The SLSN “Gaia6apd” was discovered by the European Gaia satellite, and at a distance of about one and one-half billion light-years it is the second-closest SLSN discovered to date.


    ESA/GAIA

    It is also special in another way: it is extraordinarily bright in the ultraviolet, nearly four times brighter than the next nearest known SLSN despite the fact that in the optical both have comparable luminosities. CfA astronomers Matthew Nicholl, Edo Berger, Peter Blanchard, Dan Milisavljevic, and Peter Challis and their colleagues used facilities at the CfA’s MMT and Fred Lawrence Whipple Observatory to track the changing emission of this source from immediately after its discovery and continuing for one hundred and fifty days.


    CfA MMT Telescope at the summit of Mount Hopkins near Tucson, Arizona, USA


    CfA Whipple Observatory, near Amado, Arizona on the slopes of Mount Hopkins

    The long time coverage revealed that the UV emission eventually faded to a level typical for normal supernovae, providing some clues to the mechanisms responsible. The scientists review all the known data and conclude that the most likely source is an internal central engine like a rapidly spinning neutron star. They also emphasize the key role that UV wavelengths played in diagnosing the mechanisms and urge that future studies of SLSN include UV coverage.

    Reference(s):

    “An Ultraviolet Excess in the Superluminous Supernova Gaia16apd Reveals a Powerful Central Engine,” M. Nicholl, E. Berger, R. Margutti, P. K. Blanchard, D. Milisavljevic, P. Challis, B. D. Metzger, and R. Chornock, ApJLett 835, 8, 2017.

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    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 6:20 pm on November 28, 2016 Permalink | Reply
    Tags: , , , , Matching Supernovae to Galaxies, Supernovae   

    From AAS NOVA: “Matching Supernovae to Galaxies” 

    AASNOVA

    American Astronomical Society

    28 November 2016
    Susanna Kohler

    1
    Not every supernova’s host galaxy is as easy to identify as that of SN 1994D, seen in the outskirts of galaxy NGC 4526 in this Hubble image. Automated matching of supernovae to their host galaxies will likely be necessary for large upcoming surveys. [NASA/ESA]

    One of the major challenges for modern supernova surveys is identifying the galaxy that hosted each explosion. Is there an accurate and efficient way to do this that avoids investing significant human resources?

    Why Identify Hosts?

    2
    One problem in host galaxy identification. Here, the supernova lies between two galaxies — but though the centroid of the galaxy on the right is closer in angular separation, this may be a distant background galaxy that is not actually near the supernova. [Gupta et al. 2016]

    Supernovae are a critical tool for making cosmological predictions that help us to understand our universe. But supernova cosmology relies on accurately identifying the properties of the supernovae — including their redshifts. Since spectroscopic followup of supernova detections often isn’t possible, we rely on observations of the supernova host galaxies to obtain redshifts.

    But how do we identify which galaxy hosted a supernova? This seems like a simple problem, but there are many complicating factors — a seemingly nearby galaxy could be a distant background galaxy, for instance, or a supernova’s host could be too faint to spot.

    3
    The authors’ algorithm takes into account “confusion”, a measure of how likely the supernova is to be mismatched. In these illustrations of low (left) and high (right) confusion, the supernova is represented by a blue star, and the green circles represent possible host galaxies. [Gupta et al. 2016]

    Turning to Automation

    Before the era of large supernovae surveys, searching for host galaxies was done primarily by visual inspection. But current projects like the Dark Energy Survey’s Supernova Program is finding supernovae by the thousands, and the upcoming Large Synoptic Survey Telescope will likely discover hundreds of thousands. Visual inspection will not be possible in the face of this volume of data — so an accurate and efficient automated method is clearly needed!

    Dark Energy Icon
    Dark Energy Camera. Built at FNAL
    Dark Energy Camera [DECam]. Built at FNAL

    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile
    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo

    LSST
    LSST/Camera, built at SLAC
    LSST/Camera, built at SLAC

    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST telescope, currently under construction at Cerro Pachón Chile

    To this end, a team of scientists led by Ravi Gupta (Argonne National Laboratory) has recently developed a new automated algorithm for matching supernovae to their host galaxies. Their work builds on currently existing algorithms and makes use of information about the nearby galaxies, accounts for the uncertainty of the match, and even includes a machine learning component to improve the matching accuracy.

    Gupta and collaborators test their matching algorithm on catalogs of galaxies and simulated supernova events to quantify how well the algorithm is able to accurately recover the true hosts.

    4
    The matching algorithm’s accuracy (“purity”) as a function of the true supernova-host separation, the supernova redshift, the true host’s brightness, and the true host’s size. [Gupta et al. 2016]

    Successful Matching

    The authors find that when the basic algorithm is run on catalog data, it matches supernovae to their hosts with 91% accuracy. Including the machine learning component, which is run after the initial matching algorithm, improves the accuracy of the matching to 97%.

    The encouraging results of this work — which was intended as a proof of concept — suggest that methods similar to this could prove very practical for tackling future survey data. And the method explored here has use beyond matching just supernovae to their host galaxies: it could also be applied to other extragalactic transients, such as gamma-ray bursts, tidal disruption events, or electromagnetic counterparts to gravitational-wave detections.

    Citation

    Ravi R. Gupta et al 2016 AJ 152 154. doi:10.3847/0004-6256/152/6/154

    See the full article here .

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  • richardmitnick 9:29 am on November 8, 2016 Permalink | Reply
    Tags: , , , Scraps of brightest exploding stars stretch over time, Supernovae   

    From COSMOS: “Scraps of brightest exploding stars stretch over time” 

    Cosmos Magazine bloc

    COSMOS

    08 November 2016
    Belinda Smith

    The inner layer of a superluminous supernovae has elongated in a matter of weeks, new observations show.

    1
    RCW 103, the remains of a supernova explosion located about 9,000 light-years from Earth. It’s nothing compared to superluminous supernovae, though – and a new study suggests the big ones have a couple of ejecta layers. X-ray: NASA / CXC / University of Amsterdam / N.Rea et al; Optical: DSS

    Some of the biggest and brightest exploding stars don’t keep a spherical shape, new observations show, but may periodically stretch into a hot dog bun shape.

    Cosimo Inserra from Queen’s University Belfast in the UK and colleagues measured polarised light, which gives information about asymmetries of the source, emanating from the superluminous supernova 2015bn. They found it changed shape over the course of a couple of months, pulling from a ball into an ellipsoid after peak brightness.

    The work, published in The Astrophysical Journal, provides another insight into the lifecycle of these strange cosmic objects.

    Supernovae are produced when a star in its death throes and collapses on itself, blasting a shell of material away from a black hole or a dense, spinning object with an immense magnetic field called a magnetar left in the centre.

    Superluminous supernovae, as their name suggests, are particularly bright – but they’re mysterious.

    While they explode with billions of times the energy of the sun – and last longer than a typical supernova, stretching months instead of weeks – astronomers have only known of their existence for the past six years or so.

    One of the closest superluminous supernovae – SN 2015bn – is fading in visible light, but undulating in the ultraviolet part of the spectrum. This, astronomers think, is the result of a magnetar reheating material around it, which results in a burst of ejecta every 30 to 50 days.

    But while it was ramping up to peak brightness, Cosimo and his colleagues trained a spectrograph on Chile’s Very Large Telescope on SN 2015bn to detect polarised light.

    ESO/VLT at Cerro Paranal, Chile
    ESO/VLT at Cerro Paranal, Chile

    Where unpolarised light waves move in, say, horizontal and vertical planes, polarised light moves in a single plane. Measuring polarised light – called polarimetry – and analysing it with come nifty calculations can give astronomers the rough shape of an object, such as the layers of supernova ejecta.

    The best fitting model comprised two layers of ejecta. Some 24 days before peak brightness, SN 2015bn’s outside ejecta layer was the same shape as the inner – like a soccer ball inside a basketball.

    But 28 days after the brightness started waning, more polarised light intimated that the inner ejecta had morphed into an ellipsoid while the outer later stayed roughly spherical – like a small rounded Australian football in a basketball.

    So what does this mean?

    The axisymmetric shape, the researchers write, is in line with a core-collapse explosion. A central inner engine of a magnetar or black hole pumps energy into the layers, causing the asymmetry over time.

    As to whether the shape is typical for a superluminous supernova or not is unknown. More observations and detailed modelling of other superluminous supernovae – and time – will tell.

    See the full article here .

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  • richardmitnick 9:48 am on November 6, 2016 Permalink | Reply
    Tags: , , , , , , Supernovae   

    From CfA: “Pulsar Wind Nebulae” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    November 4, 2016

    Neutron stars are the detritus of supernova explosions, with masses between one and several suns and diameters only tens of kilometers across. A pulsar is a spinning neutron star with a strong magnetic field; charged particles in the field radiate in a lighthouse-like beam that can sweep past the Earth with extreme regularity every few seconds or less. A pulsar also has a wind, and charged particles, sometimes accelerated to near the speed of light, form a nebula around the pulsar: a pulsar wind nebula. The particles’ high energies make them strong X-ray emitters, and the nebulae can be seen and studied with X-ray observatories. The most famous example of a pulsar wind nebula is the beautiful and dramatic Crab Nebula.

    Supernova remnant Crab nebula. NASA/ESA Hubble
    Supernova remnant Crab nebula. NASA/ESA Hubble

    When a pulsar moves through the interstellar medium, the nebula can develop a bow-shaped shock. Most of the wind particles are confined to a direction opposite to that of the pulsar’s motion and form a tail of nebulosity. Recent X-ray and radio observations of fast-moving pulsars confirm the existence of the bright, extended tails as well as compact nebulosity near the pulsars. The length of an X-ray tail can significantly exceed the size of the compact nebula, extending several light-years or more behind the pulsar.

    CfA astronomer Patrick Slane was a member of a team that used the Chandra X-ray Observatory to study the nebula around the pulsar PSR B0355+54, located about 3400 light-years away.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    The pulsar’s observed movement over the sky (its proper motion) is measured to be about sixty kilometer per second. Earlier observations by Chandra had determined that the pulsar’s nebula had a long tail, extending over at least seven light-years (it might be somewhat longer, but the field of the detector was limited to this size); it also has a bright compact core. The scientists used deep Chandra observations to examine the nebula’s faint emission structures, and found that the shape of the nebula, when compared to the direction of the pulsar’s motion through the medium, suggests that the spin axis of the pulsar is pointed nearly directly towards us. They also estimate many of the basic parameters of the nebula including the strength of its magnetic field, which is lower than expected (or else turbulence is re-accelerating the particles and modifying the field). Other conclusions include properties of the compact core and details of the physical mechanisms powering the X-ray and radio radiation.
    Reference(s):

    Deep Chandra Observations of the Pulsar Wind Nebula Created by PSR B0355+54</emKlingler, Noel; Rangelov, Blagoy; Kargaltsev, Oleg; Pavlov, George G.; Romani, Roger W.; Posselt, Bettina; Slane, Patrick; Temim, Tea; Ng, C.-Y.; Bucciantini, Niccolò; Bykov, Andrei; Swartz, Douglas A.; Buehler, Rolf, ApJ 2016 (in press).

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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.

     
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