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  • richardmitnick 7:04 pm on February 22, 2019 Permalink | Reply
    Tags: "Supercomputing Neutron Star Structures and Mergers", , Bridges at Pittsburgh Supercomputer Center, , , , Stampede2 at the Texas Advanced Computing Center (TACC), , Supernovae,   

    From insideHPC: “Supercomputing Neutron Star Structures and Mergers” 

    From insideHPC

    1
    This image of an eccentric binary neutron star system’s close encounter is an example of the large surface gravity wave excitations, which are similar to ocean waves found in very deep water. Credit: William East, Perimeter Institute for Theoretical Physics


    Perimeter Institute in Waterloo, Canada

    Over at XSEDE, Kimberly Mann Bruch & Jan Zverina from the San Diego Supercomputer Center write that researchers are using supercomputers to create detailed simulations of neutron star structures and mergers to better understand gravitational waves, which were detected for the first time in 2015.

    SDSC Dell Comet* supercomputer

    During a supernova, a single massive star explodes – some die and form black holes while others survive, depending on the star’s mass. Some of these supernova survivors are stars whose centers collapse and their protons and electrons form into a neutron star, which has an average gravitational pull that is two billion times the gravity on Earth.

    Researchers from the U.S., Canada, and Brazil have been focusing on the construction of a gravitational wave model for the detection of eccentric binary neutron stars. Using Comet* at the San Diego Supercomputer Center (SDSC) and Stampede2 at the Texas Advanced Computing Center (TACC), the scientists performed simulations of oscillating binary neutron stars to develop a novel model to predict the timing of various pericenter passages, which are the points of closest approach for revolving space objects.

    Texas Advanced Computer Center

    TACC DELL EMC Stampede2 supercomputer

    Their study, Evolution of Highly Eccentric Binary Neutron Stars Including Tidal Effects was published in Physical Review D. Frans Pretorius, a physics professor at Princeton University, is the Principal Investigator on the allocated project.

    “Our study’s findings provide insight into binary neutron stars and their role in detecting gravitational waves,” according to co-author Huan Yang, with the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada. “We can see that the oscillation of the stars significantly alters the trajectory and it is important to mention the evolution of the modes. For this case, during some of the later close encounters, the frequency of the orbit is larger when this evolution is tracked – compared to when it is not – as energy and angular momentum are taken out of the neutron star oscillations and put back into orbit.”

    In other words, probing gravitational waves from eccentric binary neutron stars provides a unique opportunity to observe neutron star oscillations. Through these measurements, researchers can infer the internal structure of neutron stars.

    “This is analogous to the example of ‘hearing the shape on a drum,’ where the shape of a drumhead can be determined by measuring frequencies of its modes,” said Yang. “By ‘hearing’ the modes of neutron stars with gravitational waves, the star’s size and internal structure will be similarly determined, or at least constrained.”

    “In particular, our dynamical space-time simulations solve the equations of Einstein’s theory of general relativity coupled to perfect fluids,” said co-author Vasileios Paschalidis, with the University of Arizona’s Theoretical Astrophysics Program. “Neutron star matter can be described as a perfect fluid, therefore the simulations contain the necessary physics to understand how neutron stars oscillate due to tidal interactions after every pericenter passage, and how the orbit changes due to the excited neutron star oscillations. Such simulations are computationally very expensive and can be performed only in high-performance computing centers.”

    “XSEDE resources significantly accelerated our scientific output,” noted Paschalidis, whose group has been using XSEDE for well over a decade, when they were students or post-doctoral researchers. “If I were to put a number on it, I would say that using XSEDE accelerated our research by a factor of three or more, compared to using local resources alone.”

    Neutron Star Mergers Form the Cauldron that Brews Gravitational Waves

    Merging neutron stars. Image Credit: Mark Garlick, University of Warwick.

    The merger of two neutron stars produces a hot (up to one trillion degrees Kelvin), rapidly rotating massive neutron star. This remnant is expected to collapse to form a black hole within a timescale that could be as short as one millisecond, or as long as many hours, depending on the sum of the masses of the two neutron stars.

    Featured in a recent issue of the Monthly Notices of the Royal Astronomical Society, Princeton University Computational and Theoretical Astrophysicist David Radice and his colleagues presented results from their simulations of the formation of neutron star merger remnants surviving for at least one tenth of a second. Radice turned to XSEDE for access to Comet, Stampede2, and Bridges, which is based at the Pittsburgh Supercomputing Center (PSC).

    Pittsburgh Supercomputer Center

    Bridges supercomputer at PSC

    It has been long thought that this type of merger product would be driven toward solid-body rotation by turbulent angular momentum transport, which acts as an effective viscosity. However, Radice and his collaborators discovered that the evolution of these objects is actually more complex.

    4
    The massive neutron star shown in this three-dimensional rendition of a Comet-enabled simulation shows the emergence of a wind driven by neutrino radiation. The star is surrounded by debris expelled during and shortly after the merger. Credit: David Radice, Princeton University

    “We found that long-lived neutron star merger remnants are born with so much angular momentum that they are unable to reach solid body rotation,” said Radice. “Instead, they are viscously unstable. We expect that this instability will result in the launching of massive neutron rich winds. These winds, in turn, will be extremely bright in the UV/optical/infrared bands. The observation of such transients, in combination with gravitational-wave events or short gamma-ray bursts, would be ‘smoking gun’ evidence for the formation of long-lived neutron star merger remnants.”

    If detected, the bright transients predicted in this study could allow astronomers to measure the threshold mass below which neutron star mergers do not result in rapid black hole formation. This insight would be key in the quest to understand the properties of matter at extreme densities found in the hearts of neutron stars.

    Radice’s research used 35 high-resolution, general-relativistic neutron star merger simulations, which calculated the geometry of space-time as predicted by Einstein’s equations and simulated the neutron star matter using sophisticated microphysical models. On average, one of these simulations required about 300,000 CPU-hours.

    “My research would not be possible without XSEDE,” said Radice, who has used XSEDE resources since 2013, and for this study collaborated with Lars Koesterke at TACC to run his code efficiently on Stampede2. Specifically, this work was conducted in the context of an XSEDE Extended Collaborative Support Services (ECSS) project, which will be of benefit to future research.”

    “The cost can be up to a factor of three times higher for the selected models that were run at even higher resolution and depending on the detail level in the microphysics,” added Radice. “Because of the unique requirements of this study, which included a large number of intermediate-size simulations and few larger calculations, a key enabler was the availability of a combination of capability and capacity supercomputers including Comet and Bridges.”

    See the full article here .

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    Founded on December 28, 2006, insideHPC is a blog that distills news and events in the world of HPC and presents them in bite-sized nuggets of helpfulness as a resource for supercomputing professionals. As one reader said, we’re sifting through all the news so you don’t have to!

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  • richardmitnick 11:39 am on February 9, 2019 Permalink | Reply
    Tags: , , , , First observed in 2008 a binary system known as IGR J18245–2452 from its x-ray outbursts and PSR J1824–2452I for its radio emissions, , , , Supernovae, The fastest millisecond pulsar PSR J1748–2446ad   

    From Medium: “IGR J18245–2452: The most important neutron star you’ve never heard of” 

    From Medium

    Jan 21, 2019
    Graham Doskoch

    Astronomers have spent thirty years on the theory behind how millisecond pulsars form. Now we know they got it right.

    Neutron stars are known for their astonishing rotational speeds, with most spinning around their axes many times each second. The mechanism behind this is simple: When a fairly massive star several times the radius of the Sun collapses into a dense ball about ten kilometers in diameter, conservation of angular momentum dictates that it must spin quicker.

    However, one class of neutron stars can’t be explained this way: millisecond pulsars. These exotic objects spin hundreds of times each second, with the fastest, PSR J1748–2446ad, rotating at over 700 Hertz! Since their discovery in the 1980s, a slightly different evolutionary path has been proposed. After studying dozens of systems, astronomers theorized that millisecond pulsars are very old — old enough that they’ve lost much of their original angular momentum to radiation. However, they’re also in binary systems, and under certain conditions, a companion star can transfer matter — and thus angular momentum — to the pulsar, spinning it back up again.

    1
    A plot of the periods and magnetic fields of pulsars. Millisecond pulsars have extremely short periods, and comparatively weak magnetic fields. Image credit: Swinburne University of Technology

    During this period of accretion, the system should become an x-ray binary, featuring strong emission from the hot plasma in the neutron star’s accretion disk. There should also be periods where the neutron star behaves like an ordinary radio pulsar, emitting radio waves we can detect on Earth. If we could detect both types of radiation from a single system, it might be the clinching bit of evidence for the spin-up model of millisecond pulsar formation.

    In 2013, astronomers discovered just that: a binary system known as IGR J18245–2452 from its x-ray outbursts, and PSR J1824–2452I for its radio emissions. First observed in 2008, it had exhibited both radio pulsations and x-ray outbursts within a short period of time, clear evidence of the sort of transitional stage everyone had been looking for. This was it: a confirmation of the ideas behind thirty years of work on how these strange systems form.

    2
    INTEGRAL observations of IGR J18245–2452 from February 2013 (top) and March/April 2013 (bottom). The system is only visible in x-rays in the second period. Image credit: ESA/INTEGRAL/IBIS/Jörn Wilms.

    ESA/Integral

    The 2013 outburst

    Towards the end of March of 2013, the INTEGRAL and Swift space telescopes detected x-rays from an energetic event coming from the core of the globular cluster M28 (Papitto et al. 2013).

    NASA Neil Gehrels Swift Observatory

    It appeared to be an outburst of some kind — judging by the Swift observations, likely a thermonuclear explosion. A number of scenarios can lead to x-ray transients, including novae and certain types of supernovae. Binary systems are often the culprits, where mass can be transferred from one star or compact object to another.

    3
    Fig. 7, Papitto et al. Swift data from observations of an outburst show its characteristic exponentially decreasing cooling.

    One thermonuclear burst observed by Swift followed a time evolution profile expected for such a detonation: An increase in luminosity for 10 seconds, followed by an exponential decrease with a time constant of 38.9 seconds. This decrease represents the start of post-burst cooling. The other outbursts from the system should have had similar profiles characteristic of x-ray-producing thermonuclear explosions, and indeed later observations of the system have confirmed that this is indeed the case (De Falco et al. 2017 [Astronomy and Astrophysics]), albeit with slightly different rise times and decay constants.

    To determine the identity of the transient, now designated IGR J18245–2452, astronomers made follow-up observations using the XMM-Newton telescope.

    ESA/XMM Newton

    The nature of the outburst would determine how it evolved over time. For instance, supernovae (usually) decrease in brightness over the course of weeks or months. In this case, however, the x-rays were still detected — albeit a bit weaker. More surprisingly, the strength of the emission appeared to be modulated, varying with a period of 3.93 milliseconds.

    Such a short period seemed to indicate that a pulsar might be responsible. The team checked databases of known radio pulsars and found one that matched the x-ray source: PSR J1824–2452I, a millisecond pulsar in a binary system. Even after this radio counterpart had been found, however, two questions remained: Were these x-ray pulses new or a long-term process, and how did they relate to the radio emission?

    Diving into the archives

    A handy tool for observational astronomers is archival images. By looking at observations taken months, years or decades before an event, scientists can — if they’re lucky — peek into the past to see what an object of interest looked like long before it became interesting. Archival data is often of use for teams studying supernovae, as even a previously uninteresting or unnoticed star can tell the story of a supernova’s progenitor.

    4
    Fig. 3, Papitto et al. Chandra images from 2008, showing the system in quiescent (top) and active (bottom) states.

    NASA/Chandra X-ray Telescope

    In this case, Papitto et al. looked at Chandra observations from 2008, comparing them with new data from April 2013. They found x-ray variability occurring shortly after a period of radio activity by the pulsar, indicating that the system had switched off its radio emissions and started emitting x-rays. This was extremely interesting, because new observations with three sensitive radio telescopes — Green Bank, Parkes, and Westerbork — indicated that the pulsar was no longer active in radio waves.

    Green Bank Radio Telescope, West Virginia, USA, now the center piece of the GBO, Green Bank Observatory, being cut loose by the NSF

    CSIRO/Parkes Observatory, located 20 kilometres north of the town of Parkes, New South Wales, Australia

    Westerbork Synthesis Radio Telescope, an aperture synthesis interferometer near World War II Nazi detention and transit camp Westerbork, north of the village of Westerbork, Midden-Drenthe, in the northeastern Netherlands

    It was possible that the pulsar had been eclipsed and emission was ongoing, and this may indeed have happened at some points, but was not likely to be the main factor behind the apparent quiescence.

    A few weeks later, however, the exact opposite happened: the pulsar exited its quiescent radio state and was again picked up by the three radio telescopes. In short, over a period of months, it had oscillated between behaving like an x-ray binary and a normal millisecond pulsar. Finally, x-ray observations had conclusively shown that this sort of bizarre transitional state was possible!

    The mechanism

    IGR J18245–2452 spends the vast majority of its time in what is known as a “quiescent” state, during which there is comparatively little x-ray activity. The pulsar’s magnetosphere exerts a pressure on the infalling gas, forming a disk at a suitable distance from the surface. Eventually, however, there is enough buildup that an x-ray outburst occurs, lasting for a few months. The outburst decreases the mass accretion rate, and the magnetosphere pushes away much of the transferred gas, allowing radio pulsations to take place once more.

    5
    Fig. 2, De Falco et al. Over a period of a few weeks, IGR J18245–2452 underwent a number of individual x-ray outbursts, themselves indicative of a brief period of x-ray activity and radio silence.

    It’s expected that the pulsar will eventually be spun-up until its rotational period is on the order of a millisecond or so. It will cease x-ray emissions, and be visible mainly through radio pulses. All of this, however, is far in the future, and during our lifetimes, IGR J18245–2452 will stay in its current transitional state, halfway between an x-ray binary and a millisecond pulsar.

    Women in STEM – Dame Susan Jocelyn Bell Burnell

    Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

    See the full article here .

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    About Medium

    Medium is an online publishing platform developed by Evan Williams, and launched in August 2012. It is owned by A Medium Corporation. The platform is an example of social journalism, having a hybrid collection of amateur and professional people and publications, or exclusive blogs or publishers on Medium, and is regularly regarded as a blog host.

    Williams developed Medium as a way to publish writings and documents longer than Twitter’s 140-character (now 280-character) maximum.

     
  • richardmitnick 10:48 am on December 28, 2018 Permalink | Reply
    Tags: , , , , , Did a nearby supernova cause one of Earth’s mass extinctions?, Supernovae   

    From Astronomy Magazine: “Did a nearby supernova cause one of Earth’s mass extinctions?” 

    Astronomy magazine

    From Astronomy Magazine

    December 13, 2018
    Alison Klesman

    Astronomers say radiation arriving from a powerful stellar explosion may be the event that wiped coastal ocean animals off the planet 2.6 million years ago.

    1
    This composite image shows supernova remnant 1E 0102.2-7219, which lies 190,000 light-years away. The supernova that may have caused a mass extinction on Earth was much closer, only about 150 light-years distant. X-ray (NASA/CXC/MIT/D.Dewey et al. & NASA/CXC/SAO/J.DePasquale); Optical (NASA/STScI)

    NASA/Chandra X-ray Telescope

    NASA/ESA Hubble Telescope

    Supernovae are the explosive end stages of massive stars. About 2.6 million years ago, one such supernova lit up Earth’s sky from about 150 light-years away. A few hundred years later, after the new star had long since faded from the sky, cosmic rays from the event finally reached Earth, slamming into our planet. Now, a group of researchers led by Adrian Melott at the University of Kansas believes this cosmic onslaught is linked to a mass extinction of ocean animals roaming Earth’s waters at the time — including the Megalodon. Their work was published November 27 in Astrobiology.

    “Supernovae should have affected Earth at some time or another,” Melott said in a press release. However, in the past, it’s been hard to determine exactly how or when such events would have had an effect. But, according to the group’s paper, “a newly documented marine megafaunal extinction” lines up with the arrival of a potentially lethal influx of radiation, indicating they might be able to pin a particular supernova on a particular event.

    That event, which occurred at the Pliocene-Pleistocene boundary, caused about 36 percent of the genera in coastal waters — where the penetration of radiation would have been greater in the shallower water — to go extinct. “We have evidence of nearby [supernova] events at a specific time. We know about how far away they were, so we can actually compute how that would have affected Earth and compare it to what we know about what happened at that time,” Melott said.

    Incoming!

    The killer radiation came in the form of cosmic rays made up of fast-moving muons, which are a few hundred times the mass of an electron, according to Melott. “They’re very penetrating. Even normally, there are lots of them passing through us. Nearly all of them pass through harmlessly, yet about one-fifth of our radiation dose comes by muons,” he said.

    But what about under abnormal conditions, such as the wave of material from a supernova? “When this wave of cosmic rays hits, multiply those muons by a few hundred. Only a small fraction of them will interact in any way, but when the number is so large and their energy so high, you get increased mutations and cancer,” Melott said. Based on the rates of muons hitting Earth from the stellar explosion, the team estimated that in human-sized animals, the cancer rate would increase by about 50 percent. But in larger animals, that effect would have also been larger. “For an elephant or a whale, the radiation dose goes way up,” he said. And because high-energy muons can penetrate hundreds of yards into water, they could have peppered the coastal waters where the extinctions occurred, essentially targeting the animals that lived there for death.

    2
    Our Local Bubble is of a bubble of hot, diffuse gas that was likely generated by one or more supernovae. NASA; modified from original version by Wikipedia User Geni.

    Tracing the Source

    The other piece of the puzzle was pinpointing the event that could have caused that wave of radiation. Iron-60 is a radioactive isotope of iron with a half-life of about 2.6 million years — which means that any iron-60 that formed with Earth is now long gone. Thus, the only way scientists could still find iron-60 today is if it arrived via cosmic means, such as “raining down” in the wave from a supernova. And there’s a huge spike of iron-60 that was deposited about 2.6 million years ago, indicating the material from a supernova event reached us then.

    As for where that supernova came from, our Sun sits inside what astronomers call the Local Bubble. It’s a relatively empty area of the interstellar medium (ISM) that fills the space between stars. The Local Bubble is a 300-light-year-wide region filled with hot, diffuse gas, bounded by the cold, dense gas of the “regular” ISM. In our region of the galaxy, several bubbles exist, and astronomers think these bubbles — including our own — were caused by supernovae, whose energy can sweep away material and heat anything that remains, forming just such a bubble.

    The Local Bubble may have been caused by not one, but a chain of supernovae, one of which went off extremely close to Earth 2.6 million years ago, depositing that layer of radioactive material. And the Local Bubble itself could have exacerbated the amount of cosmic rays Earth received, increasing the deadliness of such events. According to Melott, the boundaries of the bubble could have reflected cosmic rays back when they hit it, creating a “cosmic-ray bath” lasting 10,000–100,000 years for each supernova. A chain of supernovae going off relatively close to each other in time could send cosmic rays bouncing throughout the Local Bubble for millions of years, he said.

    All of this boils down to a tantalizing connection between the supernovae that clearly changed our local region of the galaxy and an unexplained major extinction event. “There really hasn’t been any good explanation for the marine megafaunal extinction,” Melott concluded. “This could be one.”

    See the full article here .


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  • richardmitnick 2:25 pm on October 12, 2018 Permalink | Reply
    Tags: , , , , , , Supernovae, This neutron star named RX J0806.4-4123   

    From Pennsylvania State University: “The surprising environment of an enigmatic neutron star” 

    Penn State Bloc

    From Pennsylvania State University

    September 17, 2018
    Bettina Posselt
    bup13@psu.edu
    Work Phone:
    (814) 863-9341

    Sam Sholtis
    sjs144@psu.edu
    Work Phone:
    814-865-1390

    1
    Infrared image of a neutron star (source on right in box) with an extended infrared emission obtained from observations with the Hubble Space Telescope. The blue circle indicates the pulsar’s X-ray position (obtained with the Chandra X-ray Space Telescope), the cross marks the position of the pulsar in the UV-Optical (measured with the Hubble Space Telescope). Credit: Bettina Posselt, Penn State

    NASA/ESA Hubble Telescope

    NASA/Chandra X-ray Telescope

    An unusual infrared emission detected by the Hubble Space Telescope from a nearby neutron star could indicate that the pulsar has features never before seen. The observation, by a team of researchers at Penn State, Sabanci University in Turkey, and the University of Arizona, could help astronomers better understand the evolution of neutron stars — the incredibly dense remnants of massive stars after a supernova. A paper describing the research and two possible explanations for the unusual finding appears Sept. 17 in The Astrophysical Journal.

    “This particular neutron star belongs to a group of seven nearby X-ray pulsars — nicknamed ‘the Magnificent Seven’ — that are hotter than they ought to be considering their ages and available energy reservoir provided by the loss of rotation energy,” said Bettina Posselt, associate research professor of astronomy and astrophysics at Penn State and the lead author of the paper. “We observed an extended area of infrared emissions around this neutron star — named RX J0806.4-4123 — the total size of which translates into about 200 astronomical units, or 2.5 times the orbit of Pluto around the Sun, at the assumed distance of the pulsar.”

    This is the first neutron star in which an extended emission has been seen only in the infrared. The researchers suggest two possibilities that could explain the extended infrared emission seen by the Hubble Space Telescope. The first is that there is a disk of material — possibly mostly dust — surrounding the pulsar.

    “One theory is that there could be what is known as a ‘fallback disk’ of material that coalesced around the neutron star after the supernova,” said Posselt. “Such a disk would be composed of matter from the progenitor massive star. Its subsequent interaction with the neutron star could have heated the pulsar and slowed its rotation. If confirmed as a supernova fallback disk, this result could change our general understanding of neutron star evolution.”

    2
    Animated llustrated GIF showing a neutron star with a circum-pulsar disk. If seen at the proper angle the scattered emission from the inner part of the disk could produce the extended infrared emission observed by astronomers around the neutron star RX J0806.4-4123.
    IMAGE: Nahks Tr’Ehnl, Penn State

    The second possible explanation for the extended infrared emission from this neutron star is a “pulsar wind nebula.”

    “A pulsar wind nebula would require that the neutron star exhibits a pulsar wind,” said Posselt. “A pulsar wind can be produced when particles are accelerated in the electric field that is produced by the fast rotation of a neutron star with a strong magnetic field. As the neutron star travels through the interstellar medium at greater than the speed of sound, a shock can form where the interstellar medium and the pulsar wind interact. The shocked particles would then radiate synchrotron emission, causing the extended infrared emission that we see. Typically, pulsar wind nebulae are seen in X-rays and an infrared-only pulsar wind nebula would be very unusual and exciting.”

    3
    Illustrated GIF showing a neutron star with a pulsar wind nebula produced by the interaction of the pulsar wind and the oncoming interstellar medium. A pulsar wind nebula could explain the extended infrared emission observed by astronomers around the neutron star RX J0806.4-4123. Such an infrared-only pulsar wind nebula is unusual because it implies a rather low energy of the accelerated particles.
    IMAGE: Nahks Tr’Ehnl, Penn State

    Although neutron stars are generally studied in radio and high-energy emissions, such as X-rays, this study demonstrates that new and interesting information about neutron stars can also be gained by studying them in the infrared. Using the new NASA James Webb Space Telescope, due to launch in 2021, astronomers will be able to further explore this newly opened discovery space in the infrared to better understand neutron star evolution.

    In addition to Posselt, the research team included George Pavlov and Kevin Luhman at Penn State; Ünal Ertan and Sirin Çaliskan at Sabanci University in Instanbul, Turkey; and Christina C. Williams at the University of Arizona. The research was supported by NASA, The Scientific and Technological Research Council of Turkey, the U.S. National Science Foundation, Penn State, the Penn State Eberly College of Science, and the Pennsylvania Space Grant Consortium.

    See the full article here .

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  • richardmitnick 2:32 pm on October 8, 2018 Permalink | Reply
    Tags: A new cutting-edge spectrographic instrument, , , , Blazars and cataclysmic binaries, Bursts of gravitational waves, , , , One-off events like the close passage of newly discovered minor bodies, SOXS Instrument for the NTT at La Silla, SOXS will study transient sources following triggers and alerts from telescopes satellites and detectors worldwide, Supernovae, Transients are astronomical events that — as the name suggests — are only visible for a short period of time   

    From European Southern Observatory: “ESO’s La Silla Observatory to gain cutting-edge SOXS instrument” 

    ESO 50 Large

    From European Southern Observatory

    8 October 2018

    Hans-Ulrich Käufl
    ESO
    Garching bei München, Germany
    Tel: +49 89 3200 6414
    Email: hukaufl@eso.org

    Sergio Campana
    INAF – Osservatorio astronomico di Brera
    Via E. Bianchi 46
    Merate (LC) – I-23807, Italy
    Tel: +39 02 72320418
    Email: sergio.campana@brera.inaf.it

    Calum Turner
    ESO Public Information Officer
    Garching bei München, Germany
    Tel: +49 89 3200 6670
    Cell: +49 151 1537 3591
    Email: pio@eso.org

    ESO La Silla SOXS instrument for NTT preliminary

    ESO has signed an agreement with an international consortium led by INAF, the Italian National Institute for Astrophysics, to build and operate a cutting-edge spectrographic instrument known as Son Of X-shooter, SOXS [1]. Work on this innovative instrument’s design has been underway since 2017, meaning that SOXS could be installed at La Silla as early as 2020.

    SOXS will be installed on ESO’s 3.58-metre New Technology Telescope (NTT) [see below] at the La Silla Observatory in Chile, replacing SOFI, a venerable and highly productive ESO instrument that has been operating for over 20 years.

    ESO SOFI

    Designed as a unique spectroscopic facility, SOXS will study transient sources following triggers and alerts from telescopes, satellites, and detectors worldwide.

    SOXS will provide vital spectroscopic follow-up observations to many transient surveys, and is poised to become the foremost transient follow-up instrument in the Southern hemisphere. The novel, highly specialized design of the instrument will ensure that it will have almost the same sensitivity as its progenitor, X-shooter, despite being installed on a much smaller telescope.

    ESO X-shooter on VLT on UT2 at Cerro Paranal, Chile

    Transients are astronomical events that — as the name suggests — are only visible for a short period of time. This includes some of the most fascinating astrophysical phenomena, such as supernovae and bursts of gravitational waves. It is critical that these triggers are followed up within hours, if not minutes, by dedicated spectroscopic facilities such as SOXS. Transients are being discovered at an impressive rate that will only be increased by future survey telescopes, making the combination of SOXS and the NTT a much-needed astronomical tool for capturing these fleeting events in wavelengths ranging from ultraviolet to the near-infrared.

    From its new home on the NTT at the La Silla Observatory, SOXS will follow up a variety of astronomical transients at all distance scales and from all branches of astronomy. Its targets will include fast alerts from space telescopes (such as gamma-ray bursts) or gravitational wave detectors, mid-term alerts (such as supernovae and X-ray transients), long-term monitoring of variable sources (such as blazars, and cataclysmic binaries), transit spectroscopy of extrasolar planets or one-off events like the close passage of newly discovered minor bodies. As well as its impressive ability to study transients, SOXS will also be able to carry out routine observations of objects which are simply too bright for other instruments like X-shooter to observe.

    SOXS is expected to see first light in 2020 and to start operating in 2021. The contract foresees 5 years of operation with a possible extension of another 5 years.
    Notes

    [1] SOXS (Son of X-shooter) is a development of the X-Shooter instrument installed on the VLT. The SOXS consortium consists of: INAF (Italy), the Weizmann Institute of Science (Israel), Universidad Andrés Bello & Millennium Institute of Astrophysics (Chile), University of Turku & FINCA (Finland), Queen’s University Belfast (UK), Tel Aviv University (Israel), and the Niels Bohr Institute (Denmark).

    See the full article here .


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  • richardmitnick 2:22 pm on May 12, 2018 Permalink | Reply
    Tags: , , , , , , , , Supernovae   

    From Harvard-Smithsonian Center for Astrophysics via EarthSky: “What’s a safe distance between us and a supernova?” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    EarthSky

    May 11, 2018

    And how many potentially exploding stars are located within the unsafe distance?

    A supernova is a star explosion – destructive on a scale almost beyond human imagining. If our sun exploded as a supernova, the resulting shock wave probably wouldn’t destroy the whole Earth, but the side of Earth facing the sun would boil away. Scientists estimate that the planet as a whole would increase in temperature to roughly 15 times hotter than our normal sun’s surface. What’s more, Earth wouldn’t stay put in orbit. The sudden decrease in the sun’s mass might free the planet to wander off into space. Clearly, the sun’s distance – 8 light-minutes away – isn’t safe. Fortunately, our sun isn’t the sort of star destined to explode as a supernova. But other stars, beyond our solar system, will. What is the closest safe distance? Scientific literature cites 50 to 100 light-years as the closest safe distance between Earth and a supernova.

    2
    Image of remnant of SN 1987A as seen at optical wavelengths with the Hubble Space Telescope in 2011.

    NASA/ESA Hubble Telescope

    This supernova was the closest in centuries, and it was visible to the eye alone. It was located on the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a satellite galaxy to our Milky Way. It was located approximately 168,000 light-years from Earth. Image via NASA, ESA, and P. Challis (Harvard-Smithsonian Center for Astrophysics).

    What would happen if a supernova exploded near Earth? Let’s consider the explosion of a star besides our sun, but still at an unsafe distance. Say, the supernova is 30 light-years away. Dr. Mark Reid, a senior astronomer at the Harvard-Smithsonian Center for Astrophysics, has said:

    “… were a supernova to go off within about 30 light-years of us, that would lead to major effects on the Earth, possibly mass extinctions. X-rays and more energetic gamma-rays from the supernova could destroy the ozone layer that protects us from solar ultraviolet rays. It also could ionize nitrogen and oxygen in the atmosphere, leading to the formation of large amounts of smog-like nitrous oxide in the atmosphere.”

    What’s more, if a supernova exploded within 30 light-years, phytoplankton and reef communities would be particularly affected. Such an event would severely deplete the base of the ocean food chain.

    Suppose the explosion were slightly more distant. An explosion of a nearby star might leave Earth and its surface and ocean life relatively intact. But any relatively nearby explosion would still shower us with gamma rays and other high-energy radiation. This radiation could cause mutations in earthly life. Also, the radiation from a nearby supernova could change our climate.

    No supernova has been known to erupt at this close distance in the known history of humankind. The most recent supernova visible to the eye was Supernova 1987A, in the year 1987. It was approximately 168,000 light-years away.

    Before that, the last supernova visible to the eye was was documented by Johannes Kepler in 1604. At about 20,000 light-years, it shone more brightly than any star in the night sky. It was even visible in daylight! But it didn’t cause earthly effects, as far as we know.

    How many potential supernovae are located closer to us than 50 to 100 light-years? The answer depends on the kind of supernova.

    A Type II supernova is an aging massive star that collapses. There are no stars massive enough to do this located within 50 light-years of Earth.

    But there are also Type I supernovae – caused by the collapse of a small faint white dwarf star. These stars are dim and hard to find, so we can’t be sure just how many are around. There are probably a few hundred of these stars within 50 light-years.

    The star IK Pegasi B is the nearest known supernova progenitor candidate. It’s part of a binary star system, located about 150 light-years from our sun and solar system.

    3
    Relative dimensions of IK Pegasi A (left), IK Pegasi B (lower center) and our sun (right). The smallest star here is the nearest known supernova progenitor candidate, at 150 light-years away. Image via RJHall on Wikimedia Commons.

    The main star in the system – IK Pegasi A – is an ordinary main sequence star, not unlike our sun. The potential Type I supernova is the other star – IK Pegasi B – a massive white dwarf that’s extremely small and dense. When the A star begins to evolve into a red giant, it’s expected to grow to a radius where the white dwarf can accrete, or take on, matter from A’s expanded gaseous envelope. When the B star gets massive enough, it might collapse on itself, in the process exploding as a supernova.

    What about Betelgeuse? Another star often mentioned in the supernova story is Betelgeuse, one of the brightest stars in our sky, part of the famous constellation Orion. Betelgeuse is a supergiant star. It is intrinsically very brilliant.

    RIGEL-BETELGEUSE-ANTARES Digital image ©Michael Carroll

    Such brilliance comes at a price, however. Betelgeuse is one of the most famous stars in the sky because it’s due to explode someday. Betelgeuse’s enormous energy requires that the fuel be expended quickly (relatively, that is), and in fact Betelgeuse is now near the end of its lifetime. Someday soon (astronomically speaking), it will run out of fuel, collapse under its own weight, and then rebound in a spectacular Type II supernova explosion. When this happens, Betelgeuse will brighten enormously for a few weeks or months, perhaps as bright as the full moon and visible in broad daylight.

    When will it happen? Probably not in our lifetimes, but no one really knows. It could be tomorrow or a million years in the future. When it does happen, any beings on Earth will witness a spectacular event in the night sky, but earthly life won’t be harmed. That’s because Betelgeuse is 430 light-years away.

    How often do supernovae erupt in our galaxy? No one knows. Scientists have speculated that the high-energy radiation from supernovae has already caused mutations in earthly species, maybe even human beings.

    One estimate suggests there might be one dangerous supernova event in Earth’s vicinity every 15 million years. Another says that, on average, a supernova explosion occurs within 10 parsecs (33 light-years) of the Earth every 240 million years. So you see we really don’t know. But you can contrast those numbers to the few million years humans are thought to have existed on the planet – and four-and-a-half billion years for the age of Earth itself.

    And, if you do that, you’ll see that a supernova is certain to occur near Earth – but probably not in the foreseeable future of humanity.

    See the full article here .

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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 11:45 am on March 26, 2018 Permalink | Reply
    Tags: , , , , Kepler Beyond Planets: Finding Exploding Stars, , , , Supernovae   

    From JPL-Caltech- “Kepler Beyond Planets: Finding Exploding Stars” 

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    JPL-Caltech

    March 26, 2018
    Calla Cofield
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-393-1821
    calla.e.cofield@jpl.nasa.gov

    Alison Hawkes
    Ames Research Center, California’s Silicon Valley
    650-604-0281
    alison.j.hawkesbak@nasa.gov

    Written by Elizabeth Landau
    NASA’s Exoplanet Exploration Program

    1
    A new study describes the most extreme known example of a “fast-evolving luminous transient” (FELT) supernova.Credit: NASA/JPL-Caltech.

    Astronomer Ed Shaya was in his office looking at data from NASA’s Kepler space telescope in 2012 when he noticed something unusual: The light from a galaxy had quickly brightened by 10 percent. The sudden bump in light got Shaya instantly excited, but also nervous. The effect could be explained by the massive explosion of a star — a supernova! — or, more troublingly, a computer error.

    “I just remember on that day, not knowing whether I should believe it or not,” he remembers. Rather than celebrate, he thought, “Did I make a mistake? Am I doing this all wrong?”


    This animation shows a kind of stellar explosion called a Fast-Evolving Luminous Transient. In this case, a giant star “burps” out a shell of gas and dust about a year before exploding. Most of the energy from the supernova turns into light when it hits this previously ejected material, resulting in a short, but brilliant burst of radiation. Credit: NASA/JPL-Caltech

    Stellar explosions forge and distribute materials that make up the world in which we live, and also hold clues to how fast the universe is expanding. By understanding supernovae, scientists can unlock mysteries that are key to what we are made of and the fate of our universe. But to get the full picture, scientists must observe supernovae from a variety of perspectives, especially in the first moments of the explosion. That’s really difficult — there’s no telling when or where a supernova might happen next.

    A small group of astronomers, including Shaya, realized Kepler could offer a new technique for supernova-hunting. Launched in 2009, Kepler is best known for having discovered thousands of exoplanets. But as a telescope that stares at single patches of space for long periods of time, it can capture a vast trove of other cosmic treasures –especially the kind that change rapidly or pop in and out of view, like supernovae.

    “Kepler opened up a new way of looking at the sky,” said Jessie Dotson, Kepler’s project scientist, based at NASA’s Ames Research Center in California’s Silicon Valley. “It was designed to do one thing really well, which was to find planets around other stars. In order to do that, it had to deliver high-precision, continuous data, which has been valuable for other areas of astronomy.”

    Originally, Shaya and colleagues were looking for active galactic nuclei in their Kepler data. An active galactic nucleus is an extremely bright area at the center of a galaxy where a voracious black hole is surrounded by a disk of hot gas. They had thought about searching for supernovae, but since supernovae are such rare events, they didn’t mention it in their proposal. “It was too iffy,” Shaya said.

    Unsure if the supernova signal he found was real, Shaya and his University of Maryland colleague Robert Olling spent months developing software to better calibrate Kepler data, taking into account variations in temperature and pointing of the instrument. Still, the supernova signal persisted. In fact, they found five more supernovae in their Kepler sample of more than 400 galaxies. When Olling showed one of the signals to Armin Rest, who is now an astronomer at the Space Telescope Science Institute in Baltlimore, Rest’s jaw dropped. “I started to drool,” he said. The door had opened to a new way of tracking and understanding stellar explosions.

    Today, these astronomers are part of the Kepler Extra-Galactic Survey, a collaboration between seven scientists in the United States, Australia and Chile looking for supernovae and active galactic nuclei to explore the physics of our universe. To date, they have found more than 20 supernovae using data from the Kepler spacecraft, including an exotic type reported by Rest in a new study in Nature Astronomy. Many more are currently being recorded by Kepler’s ongoing observations.

    “We have some of the best-understood supernovae,” said Brad Tucker, astronomer at the Mt. Stromlo Observatory at the Australian National University, who is part of the Kepler Extra-Galactic Survey.


    This animation shows the explosion of a white dwarf, an extremely dense remnant of a star that can no longer burn nuclear fuel at its core. In this “type Ia” supernova, white dwarf’s gravity steals material away from a nearby stellar companion. When the white dwarf reaches an estimated 1.4 times the current mass of the Sun, it can no longer sustain its own weight, and blows up. Credit: NASA/JPL-Caltech

    Why do we care about supernovae?

    A longstanding mystery in astrophysics is how and why stars explode in different ways. One kind of supernova happens when a dense, dead star called a white dwarf explodes. A second kind happens when a single gigantic star nears the end of its life, and its core can no longer withstand the gravitational forces acting on it. The details of these general categories are still being worked out.

    The first kind, called “type Ia” (pronounced as “one a”) is special because the intrinsic brightness of each of these supernovae is almost the same. Astronomers have used this standard property to measure the expansion of the universe and found the more distant supernovae were less bright than expected. This indicated they were farther away than scientists had thought, as the light had become stretched out over expanding space. This proved that the universe is expanding at an accelerating rate and earned those researchers the Nobel Prize in 2011. The leading theory is that a mysterious force called “dark energy” is pushing everything in the universe apart from everything else, faster and faster.

    But as astronomers find more and more examples of type Ia explosions, including with Kepler, they realize not all are created equal. While some of these supernovae happen when a white dwarf robs its companion of too much matter, others are the result of two white dwarfs merging. In fact, the white dwarf mergers may be more common. More supernova research with Kepler will help astronomers on a quest to find out if different type Ia mechanisms result in some supernovae being brighter than others — which would throw a wrench into how they are used to measure the universe’s expansion.

    “To get a better idea of constraining dark energy, we have to understand better how these type Ia supernovae are formed,” Rest said.


    This animation shows the merger of two white dwarfs. A white dwarf is an extremely dense remnant of a star that can no longer burn nuclear fuel at its core. This is another way that a “type Ia” supernova occurs. Credit: NASA/JPL-Caltech

    Another kind of supernova, the “core collapse” variety, happens when a massive star ends its life in an explosion. This includes “Type II” supernovae. These supernovae have a characteristic shockwave called the “shock breakout,” which was captured for the first time in optical light by Kepler. The Kepler Extra-Galactic Survey team, led by team member Peter Garnavich, an astrophysics professor at the University of Notre Dame in Indiana, spotted this shock breakout in 2011 Kepler data from a supernova called KSN 2011d, an explosion from a star roughly 500 times the size of our Sun. Surprisingly, the team did not find a shock breakout in a smaller type II supernova called KSN 2011a, whose star was 300 times the size of the Sun — but instead found the supernova nestled in a layer of dust, suggesting that there is diversity in type II stellar explosions, too.

    Kepler data have revealed other mysteries about supernovae. The new study led by Rest in Nature Astronomy describes a supernova from data captured by Kepler’s extended mission, called K2, that reaches its peak brightness in just a little over two days, about 10 times less than others take. It is the most extreme known example of a “fast-evolving luminous transient” (FELT) supernova. FELTs are about as bright as the type Ia variety, but rise in less than 10 days and fade in about 30. It is possible that the star spewed out a dense shell of gas about a year before the explosion, and when the supernova happened, ejected material hit the shell. The energy released in that collision would explain the quick brightening.

    Why Kepler?

    Telescopes on Earth offer a lot of information about exploding stars, but only over short periods of time — and only when the Sun goes down and the sky is clear – so it’s hard to document the “before” and “after” effects of these explosions. Kepler, on the other hand, offers astronomers the rare opportunity to monitor single patches of sky continuously for months, like a car’s dashboard camera that is always recording. In fact, the primary Kepler mission, which ran from 2009 to 2013, delivered four years of observations of the same field of view, snapping a picture about every 30 minutes. In the extended K2 mission, the telescope is holding its gaze steady for up to about three months.


    This animation shows a gigantic star exploding in a “core collapse” supernova. As molecules fuse inside the star, eventually the star can’t support its own weight anymore. Gravity makes the star collapse on itself. Core collapse supernovae are called type Ib, Ic, or II depending on the chemical elements present. Credit: NASA/JPL-Caltech

    With ground-based telescopes, astronomers can tell the supernova’s color and how it changes with time, which lets them figure out what chemicals are present in the explosion. The supernova’s composition helps determine the type of star that exploded. Kepler, on the other hand, reveals how and why the star explodes, and the details of how the explosion progresses. Using the two datasets together, astronomers can get fuller pictures of supernovae behavior than ever before.

    Kepler mission planners revived the telescope in 2013, after the malfunction of the second of its four reaction wheels — devices that help control the orientation of the spacecraft. In the configuration called K2, it needs to rotate every three months or so — marking observing “campaigns.” Members of the Kepler Extra-Galactic Survey made the case that in the K2 mission, Kepler could still monitor supernovae and other exotic, distant astrophysical objects, in addition to exoplanets.

    The possibilities were so exciting that the Kepler team devised two K2 observing campaigns especially useful for coordinating supernovae studies with ground-based telescopes. Campaign 16, which began on Dec. 7, 2017, and ended Feb. 25, 2018,included 9,000 galaxies. There are about 14,000 in Campaign 17, which is just beginning now. In both campaigns, Kepler faces in the direction of Earth so that observers on the ground can see the same patch of sky as the spacecraft. The campaigns have excited a community of researchers who can advantage of this rare coordination between Kepler and telescopes on the ground.

    3
    Infographic

    A recent possible sighting got astronomers riled up on Super Bowl Sunday this year, even if they weren’t into the game. On that “super” day, the All Sky Automated Survey for SuperNovae (ASASSN) reported a supernova in the same nearby galaxy Kepler was monitoring. This is just one of many candidate events that scientists are excited to follow up on and perhaps use to better understand the secrets of the universe.

    A few more supernovae may come from NASA’s Transiting Exoplanet Survey Satellite, (TESS) which is expected to launch on April 16. In the meantime, scientists will have a lot of work ahead of them once they receive the full dataset from K2’s supernova-focused campaigns.

    “It will be a treasure trove of supernova information for years to come,” Tucker said.

    Ames manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA’s Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

    For more information about the Kepler mission, visit:

    https://www.nasa.gov/kepler

    See the full article here .

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  • richardmitnick 3:26 pm on October 5, 2017 Permalink | Reply
    Tags: , , , , NAOJ Cray XC30 ATERUI, , Supernovae, ,   

    From NOAJ Subaru: “Surface Helium Detonation Spells End for White Dwarf” 

    NAOJ

    NAOJ

    October 4, 2017
    No writer credit

    An international team of researchers has found evidence that the brightest stellar explosions in our Universe could be triggered by helium nuclear detonation near the surface of a white dwarf star. Using Hyper Suprime-Cam mounted on the Subaru Telescope, the team detected a type Ia supernova within a day after the explosion, and explained its behavior through a model calculated using the supercomputer ATERUI.

    NAOJ Cray XC30 ATERUI, installed in the NAOJ Mizusawa campus

    1
    Figure 1: A type Ia supernova detected within a day after exploding. Taken with Hyper Suprime-Cam mounted on the Subaru Telescope. Figure without the labels is linked here. (Credit: University of Tokyo/NAOJ)

    NAOJ Subaru Hyper Suprime-Cam

    Some stars end their lives with a huge explosion called a supernova. The most famous supernovae are the result of a massive star exploding, but a white dwarf, the remnant of an intermediate mass star like our Sun, can also explode. This can occur if the white dwarf is part of a binary star system. The white dwarf accretes material from the companion star, then at some point, it might explode as a type Ia supernova.

    Because of the uniform and extremely high brightness (about 5 billion times brighter than the Sun) of type Ia supernovae, they are often used for distance measurements in astronomy. However, astronomers are still puzzled by how these explosions are ignited. Moreover, these explosions only occur about once every 100 years in any given galaxy, making them difficult to catch.

    An international team of researchers led by Ji-an Jiang, a graduate student of the University of Tokyo, and including researchers from the University of Tokyo, the Kavli Institute for the Physics and Mathematics of the Universe (IPMU), Kyoto University, and the National Astronomical Observatory of Japan (NAOJ), tried to solve this problem. To maximize the chances of finding a type Ia supernova in the very early stages, the team used Hyper Suprime-Cam (HSC) mounted on the Subaru Telescope, a combination which can capture an ultra-wide area of the sky at once. Also they developed a system to detect supernovae automatically in the heavy flood of data during the survey, which enabled real-time discoveries and timely follow-up observations.

    They discovered over 100 supernova candidates in one night with Subaru/Hyper Suprime-Cam, including several supernovae that had only exploded a few days earlier. In particular, they captured a peculiar type Ia supernova within a day of it exploding. Its brightness and color variation over time are different from any previously-discovered type Ia supernova. They hypothesized this object could be the result of a white dwarf with a helium layer on its surface. Igniting the helium layer would lead to a violent chain reaction and cause the entire star to explode. This peculiar behavior can be totally explained with numerical simulations calculated using the supercomputer ATERUI. “This is the first evidence that robustly supports a theoretically predicted stellar explosion mechanism!” said Jiang.

    This result is a step towards understand the beginning of type Ia supernovae. The team will continue to test their theory against other supernovae, by detecting more and more supernovae just after the explosion. The details of their study are to be published in Nature on October 5, 2017 (Jiang et al. 2017, A hybrid type la supernova with an early flash triggered by helium-shell detonation, Nature).

    See the full article here .

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    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

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    Okayama Astrophysical Observatory

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

     
  • richardmitnick 2:46 pm on August 17, 2017 Permalink | Reply
    Tags: , , , , , Supernovae,   

    From Many Worlds: “Of White Dwarfs, “Zombie” Stars and Supernovae Explosions” 

    NASA NExSS bloc

    NASA NExSS

    Many Words icon

    Many Worlds

    2017-08-17
    Marc Kaufman

    1
    Artistic view of the aftermath of a supernova explosion, with an unexpected white dwarf remnant. These super-dense but no longer active stars are thought to play a key role in many supernovae explosion. (Copyright Russell Kightley)

    White dwarf stars, the remnant cores of low-mass stars that have exhausted all their nuclear fuel, are among the most dense objects in the sky.

    Their mass is comparable to that of the sun, while their volume is comparable to that of Earth. Very roughly, this means the average density of matter in a white dwarf would be on the order of 1,000,000 times greater than the average density of the sun.

    Thought to be the final evolutionary state of stars whose mass is not high enough to become a neutron star — a category that includes the sun and over 97% of the other stars in the Milky Way — they are dim objects first identified a century ago but only in the last decade the subject of broad study.

    In recent years the white dwarfs have become more and more closely associated with supernovae explosions, though the processes involved remained hotly debated. A team using the Hubble Space Telescope even captured before and after images of what is hypothesized to be an incomplete white dwarf supernova. What was left behind has been described by some as a “zombie star.”

    Now a team of astronomers led by Stephane Vennes of the Czech Academy of Sciences has detected another zombie white dwarf, LP-40-365 , that they put forward as a far-flung remnant of a long-ago supernova explosion. This is considered important and unusual because it would represent a first detection of such a remnant long after the supernova conflagration.

    This dynamic is well captured in an animation accompanying the Science paper that describes the possible remnant.

    A supernova — among the most powerful forces in the universe — occurs when there is a change in the core of a star. A change can occur in two different ways, with both resulting in a thermonuclear explosion.

    Type Ia supernova occurs at the end of a single star’s lifetime. As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force. The core collapses, which results in the giant explosion of a supernova. The sun is a single star, but it does not have enough mass to become a supernova.

    The second type takes place only in binary star systems. Binary stars are two stars that orbit the same point. One of the stars, a carbon-oxygen white dwarf, steals matter from its companion star. Eventually, the white dwarf accumulates too much matter. Having too much matter causes the star to explode, resulting in a supernova.

    Type Ia supernovae, which are the result of the complete destruction of the star in a thermonuclear explosion, have a fairly uniform brightness that makes them useful for cosmology. The light emitted by the supernova explosion can be, for a short while at least, as bright as the whole of the Milky Way.

    Recently, astronomers have discovered a related form of supernova, called Type Iax, which look like Type Ia, but are much fainter. Type Iax supernovae may be caused by the partial destruction of a white dwarf star in such an explosion. If that interpretation is correct, part of the white dwarf should survive as a leftover object.

    And that leftover object is precisely what Vennes et al claim to have found.

    They have identified LP 40-365 as an unusual white dwarf with a low mass, high velocity and strange composition of oxygen, sodium and magnesium – exactly as might be expected for the leftover star from a Type Iax event. Vennes describes the white dwarf remnant his team has detected as a “compact star,” and perhaps the first of its kind in terms of the elements it contains.

    The team calculate that the explosion must have occurred between five and 50 million years ago.

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    The two inset images show before-and-after images captured by NASA’s Hubble Space Telescope of Supernova 2012Z in the spiral galaxy NGC 1309, what some call a “zombie star.”. The white X at the top of the main image marks the location of the supernova in the galaxy. A supernova typically obliterates the exploding white dwarf, or dying star. In 2014, scientists found that this faint supernova may have left behind a surviving portion of the white dwarf star.(NASA,ESA)

    In an email exchange, Vennes told me that he has been studying the local white dwarf population for thirty years.

    “These compact, dead stars tell us a lot about the “old” Milky Way, how stars were born and how they died,” he wrote.

    “Tens of thousands of these white dwarfs have been catalogued over this past century, most of them in the last decade, but we keep an eye on outliers, objects that are out of the norm. We look for exceedingly large velocity, peculiar chemical composition or abnormal mass or radii.

    “The strange case of LP40-365 came unexpectedly, but this was a classic case of serendipity in astronomy. Out of hundreds of targets we observed at the telescope, this one was uniquely peculiar. Fortunately, theorists are very imaginative and the model we adopted to interpret the observed properties of this object were only recently published. Our research on this object was certainly inspired and directed by their theory.”

    Vennes says the team was surprised to learn that the white dwarf LP40-365 is relatively bright among its peers and that similar objects did not show up in large-scale surveys such as the Sloan Digital Sky Survey.

    “This fact has convinced us that many more similarly peculiar white dwarfs await discovery. We should search among fainter, more distant samples of white dwarfs,” he wrote.

    And that search can be done by the European Space Agency’s Gaia astrometric space telescope, with follow-up observations at large telescopes such as the European Southern Observatory’s Very Large Telescope and the Gemini observatory in Chile.

    ESA/GAIA satellite

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


    Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

    “It is also likely that our adopted model involving a subluminous {faint} Type Ia supernova will be modified or even superseded by teams of theorists coming up with new ideas. But we remain confident that these new ideas would still involve a cataclysmic event on the scale of a supernova.”

    A supernova burns for only a short period of time, but it can tell scientists a lot about the universe.

    One kind of supernova has shown scientists that we live in an expanding universe, one that is growing at an ever increasing rate.

    Scientists also have determined that supernovas play a key role in distributing elements throughout the universe. When the star explodes, it shoots elements and debris into space. Many of the elements we find here on Earth are made in the core of stars.

    These elements travel on to form new stars, planets and everything else in the universe — making white dwarfs and supernovae essential to the process that ultimately led to life.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    About Many Worlds

    There are many worlds out there waiting to fire your imagination.

    Marc Kaufman is an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer, and is the author of two books on searching for life and planetary habitability. While the “Many Worlds” column is supported by the Lunar Planetary Institute/USRA and informed by NASA’s NExSS initiative, any opinions expressed are the author’s alone.

    This site is for everyone interested in the burgeoning field of exoplanet detection and research, from the general public to scientists in the field. It will present columns, news stories and in-depth features, as well as the work of guest writers.

    About NExSS

    The Nexus for Exoplanet System Science (NExSS) is a NASA research coordination network dedicated to the study of planetary habitability. The goals of NExSS are to investigate the diversity of exoplanets and to learn how their history, geology, and climate interact to create the conditions for life. NExSS investigators also strive to put planets into an architectural context — as solar systems built over the eons through dynamical processes and sculpted by stars. Based on our understanding of our own solar system and habitable planet Earth, researchers in the network aim to identify where habitable niches are most likely to occur, which planets are most likely to be habitable. Leveraging current NASA investments in research and missions, NExSS will accelerate the discovery and characterization of other potentially life-bearing worlds in the galaxy, using a systems science approach.
    The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

    President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

    Since that time, most U.S. space exploration efforts have been led by NASA, including the Apollo moon-landing missions, the Skylab space station, and later the Space Shuttle. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle and Commercial Crew vehicles. The agency is also responsible for the Launch Services Program (LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a new Space Launch System that it said would take the agency’s astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.

    NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [Hubble, Chandra, Spitzer, and associated programs. NASA shares data with various national and international organizations such as from the [JAXA]Greenhouse Gases Observing Satellite.

     
  • richardmitnick 1:34 pm on August 15, 2017 Permalink | Reply
    Tags: , , , , Supernovae,   

    From Symmetry: “All about supernovae” 2015 

    Symmetry Mag

    Symmetry

    08/25/15 [Why now?]
    Ali Sundermier

    1
    Crab nebula

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

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

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

    1. The oldest recorded supernova dates back almost 2000 years

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

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

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    SN185. Wikipedia

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    2. Many of the elements we’re made of come from supernovae

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

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

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    3. Supernovae are neutrino factories

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

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

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

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

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    4. Supernovae are powerful particle accelerators

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

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

    5. Supernovae produce radioactivity

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

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

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

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    6. A nearby supernova could cause a mass extinction

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

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

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

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

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

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    7. Supernovae light can echo through time

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

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

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

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

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    8. Supernovae were used to discover dark energy

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

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

    ASAS-SN Brutus

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

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

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

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
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