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  • richardmitnick 9:22 am on April 8, 2019 Permalink | Reply
    Tags: , and the Fate of Our Universe", , , , , , , Supernovae   

    From AAS NOVA: “Supernovae, Dark Energy, and the Fate of Our Universe” 

    AASNOVA

    From AAS NOVA

    5 April 2019
    Susanna Kohler

    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

    What’s the eventual fate of our universe? Is spacetime destined to continue to expand forever? Will it fly apart, tearing even atoms into bits? Or will it crunch back in on itself? New results from Dark Energy Survey supernovae address these and other questions.

    Uncertain Expansion

    1
    The evolution of the scale of our universe. Measurements suggest that the universe is currently expanding, but does dark energy behaves like a cosmological constant, resulting in continued accelerating expansion like now? Or might we instead be headed for a Big Rip or Big Crunch? [NASA/CXC/M. Weiss]

    At present, the fabric of our universe is expanding — and not only that, but the its expansion is accelerating. To explain this phenomenon, we invoke what’s known as dark energy — an unknown form of energy that exists everywhere and exerts a negative pressure, driving the expansion.

    Since this idea was first proposed, we’ve conducted decades of research to better understand what dark energy is, how much of it there is, and how it influences our universe.

    In particular, dark energy’s still-uncertain equation of state determines the universe’s ultimate fate. If the density of dark energy is constant in time, our universe will continue its current accelerating expansion indefinitely. If the density increases in time, the universe will end in the Big Rip — space will expand at an ever-increasing acceleration rate until even atoms fly apart. And if the density decreases in time, the universe will recollapse in the Big Crunch, ending effectively in a reverse Big Bang.

    Which of these scenarios is correct? We’re not sure yet. But there’s a project dedicated to finding out: the Dark Energy Survey (DES).

    The Hunt for Supernovae

    DES was conducted with the Dark Energy Camera at the Cerro Tololo Inter-American Observatory in Chile. After six years taking data, the survey officially wrapped up observations this past January.

    One of DES’s several missions was to make detailed measurements of thousands of supernovae. Type Ia supernovae explode with a prescribed absolute brightness, allowing us to determine their distance from observations. DES’s precise measurements of Type Ia supernovae allow us to calculate the expansion of the space between us and the supernovae, probing the properties of dark energy.

    Though DES scientists are still in the process of analyzing the tens of terabytes of data generated by the project, they recently released results from the first three years of data — including the first DES cosmology results based on supernovae.

    Refined Measurements

    2
    Constraints on the dark energy equation of state w from the DES supernova survey. Combining this data with constraints from the cosmic microwave background radiation suggest an equation of state consistent with a constant density of dark energy (w = –1). [Abbott et al. 2019]

    Using a sample of 207 spectroscopically confirmed DES supernovae and 122 low-redshift supernovae from the literature, the authors estimate the matter density of a flat universe to be Ωm = 0.321 ± 0.018. This means that only ~32% of the universe’s energy density is matter (the majority of which is dark matter); the remaining ~68% is primarily dark energy.

    From their observations, the DES team is also able to provide an estimate for the dark-energy equation of state w, finding that w = –0.978 ± 0.059. This result is consistent with a constant density of dark energy (w = –1), which would mean that our universe will continue to expand with its current acceleration indefinitely.

    These results are exciting, but they use only ~10% of the supernovae DES discovered over the span of its 5-year survey. This means that we can expect even further refinements to these measurements in the future, as the DES collaboration analyzes the remaining data!

    Citation

    “First Cosmology Results using Type Ia Supernovae from the Dark Energy Survey: Constraints on Cosmological Parameters,” T. M. C. Abbott et al 2019 ApJL 872 L30.
    https://iopscience.iop.org/article/10.3847/2041-8213/ab04fa/meta

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex Mittelmann Cold creation

    See the full article here .


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    Stem Education Coalition

    1

    AAS Mission and Vision Statement

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

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

    Adopted June 7, 2009

     
  • richardmitnick 2:21 pm on March 29, 2019 Permalink | Reply
    Tags: , , , , , Supernovae   

    From AAS NOVA: “A Rare Double-Detonation Supernova Caught in the Act” 

    AASNOVA

    From AAS NOVA

    29 March 2019
    Kerry Hensley

    1
    This representative-color X-ray and infrared image shows supernova remnant G299, which is all that’s left after a massive explosion roughly 4,500 years ago. Like the supernova studied in today’s paper, G299 met its end when a white dwarf underwent a thermonuclear detonation. [X-ray: NASA/CXC/U.Texas/S.Post et al, Infrared: 2MASS/UMass/IPAC-Caltech/NASA/NSF]

    NASA/Chandra X-ray Telescope


    Caltech 2MASS Telescopes, a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center (IPAC) at Caltech, at the Whipple Observatory on Mt. Hopkins south of Tucson, AZ, Altitude 2,606 m (8,550 ft) and at the Cerro Tololo Inter-American Observatory at an altitude of 2200 meters near La Serena, Chile.

    There’s more than just one way for a star to explode. Supernovae — perhaps the most dramatic form of star death — come in many flavors, and astronomers are still learning about the vast diversity of these stellar explosions.

    When Stars Steal Mass

    2
    This artist’s rendering depicts one kind of Type Ia supernova mechanism: the singly degenerate model, in which a white dwarf siphons mass from its companion, exceeds the Chandrasekhar mass, and explodes. [NASA/CXC/M. Weiss]

    When a white dwarf accretes gas from a binary companion and gains enough mass to exceed the Chandrasekhar limit, it can ignite in a cataclysmic explosion. This is the typical scenario for a Type Ia supernova, a common curtain call for low- to intermediate-mass stars in binary systems.

    However, this isn’t the only way a Type Ia supernova can happen. In the double-detonation model, the explosion of the white dwarf is triggered by the ignition of an accreted helium shell. In this case, the white dwarf can be far less massive than the Chandrasekhar limit, leading to unexpectedly dim explosions.

    Past studies have explored the minimum helium shell mass necessary (~0.01 solar mass) for this process and found that helium-shell detonations can efficiently cause core detonations, but there’s still plenty we don’t know about these events. The best way to learn about supernovae — double-detonation or otherwise — is to spot them soon after they happen.

    3
    A comparison of ZTF 18aaqeasu’s optical light curve (red circles) to normal (orange hexagons) and sub-luminous Type Ia supernovae. [Adapted from De et al. 2019]

    A Survey Spies a Supernova

    In May 2018, an unusual supernova was detected by the Zwicky Transient Facility, an optical survey that hunts for fleeting events like stellar flares, fast-rotating asteroids, and the visible-light counterparts of gravitational-wave events.

    Zwicky Transient Facility (ZTF) instrument installed on the 1.2m diameter Samuel Oschin Telescope at Palomar Observatory in California. Courtesy Caltech Optical Observatories

    Edwin Hubble at Caltech Palomar Samuel Oschin 48 inch Telescope, (credit: Emilio Segre Visual Archives/AIP/SPL)

    Caltech Palomar Samuel Oschin 48 inch Telescope, located in San Diego County, California, United States, altitude 1,712 m (5,617 ft)

    Within days of its detection, a team led by Kishalay De (Caltech) began to collect photometric observations and spectra of the object.

    The photometry revealed that the object, ZTF 18aaqeasu, was unusually red and less luminous than a typical Type Ia supernova, making it a good candidate for the double-detonation scenario.

    Its spectra were unusual even for a sub-luminous supernova, taking much longer to develop the silicon absorption feature typically seen in this type of event. Even stranger, the spectra exhibited a never-before-seen cutoff in the flux at short wavelengths, likely due to the presence of metals like iron and titanium.

    4
    Comparison of observed spectra (black) to helium-shell double-detonation models (green and orange). [Adapted from De et al. 2019]

    An Unusual Event

    In order to derive the properties of ZTF 18aaqeasu, De and collaborators compared their photometric and spectroscopic data to models, finding that the event was likely caused by the ignition of a 0.15 solar mass helium shell, which led to the explosion of a 0.76 solar mass white dwarf.

    The combination of a massive helium shell with a low-mass white dwarf makes ZTF 18aaqeasu unique among Type Ia supernovae; SN 2016jhr (one of the only supernovae previously linked to a helium-shell detonation event) featured a much more massive white dwarf with a less massive helium shell.

    Can we expect to find more supernovae like ZTF 18aaqeasu? Similarly luminous supernovae should be detectable out to about 1.3 billion light-years, but so far there have been none reported with similar spectral features and unusually red color. This may indicate that double-detonation events featuring massive helium shells might be rare — adding an elusive new member to the Type Ia supernova family.

    Citation

    “ZTF 18aaqeasu (SN2018byg): A Massive Helium-shell Double Detonation on a Sub-Chandrasekhar-mass White Dwarf,” Kishalay De et al 2019 ApJL 873 L18.
    https://iopscience.iop.org/article/10.3847/2041-8213/ab0aec

    See the full article here .


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    Please help promote STEM in your local schools.

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    1

    AAS Mission and Vision Statement

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

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

    Adopted June 7, 2009

     
  • richardmitnick 8:04 am on March 29, 2019 Permalink | Reply
    Tags: "Mysterious burst confounds astrophysicists", An unlucky compact object was destroyed when coming too close to a black hole – a phenomenon called a tidal disruption event, , , , , , , Supernovae, The opposing theory is that the Cow was a special type of supernova in which either a black hole or a quickly rotating highly magnetic neutron star- a magnetar is produced, Variable X-ray emission is produced by radiating gas falling into the compact objectariable X-ray emission is produced by radiating gas falling into the compact object   

    From CERN Courier: “Mysterious burst confounds astrophysicists” 


    From CERN Courier

    8 March 2019

    1
    Holy cow!

    On 16 June 2018, a bright burst of light was observed by the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Hawaii, which automatically searches for optical transient events.

    ATLAS is an asteroid impact early warning system of two telescopes being developed by the University of Hawaii and funded by NASA


    ATLAS telescope, First Asteroid Terrestrial-impact Last Alert system (ATLAS) fully operational 8/15/15 Haleakala , Hawaii, USA, Altitude 4,205 m (13,796 ft)

    The event, which received the automated catalogue name “AT2018cow”, immediately received a lot of attention and acquired a shorter name: “the Cow”. While transient objects are observed on the sky every day – caused, for example, by nearby asteroids or supernovae – two factors make the Cow intriguing. First, the very short time it took for the event to reach its extreme brightness and fade away again indicates that this event is nothing like anything observed before. Second, it took place relatively close to Earth, 200 million light years away in a star-forming arm of a galaxy in the Hercules constellation, making it possible to study the event in a wide range of wavelengths.

    Soon after the ATLAS detection, the object was observed by more than 20 different telescopes around the world, revealing it to be 10–100 times brighter than a typical supernova. In addition to optical measurements, the object was observed for several days by space-based X- and gamma-ray telescopes such as NuSTAR, XMM-Newton, INTEGRAL and Swift, which also observed it in the UV energy range, as well as by radio telescopes on Earth.

    NASA/DTU/ASI NuSTAR X-ray telescope

    ESA/XMM Newton

    ESA/Integral

    NASA Neil Gehrels Swift Observatory

    The IceCube observatory in Antarctica also identified two possible neutrinos coming from the Cow, although the detection is still compatible with a background fluctuation.

    U Wisconsin ICECUBE neutrino detector at the South Pole

    The combination of all the data – demonstrating the power of multi-messenger astronomy – confirmed that this was not an ordinary supernova, but potentially something completely different.

    Right spark

    While standard supernovae take several days to reach maximum brightness, the Cow did so in just 1.5 days, after which the brightness also started to decrease much faster than a typical supernova. Another notable feature was the lack of heavy-element decays. Normally, elements such as 56Ni produced during the explosion are the main source of supernovae brightness, but the Cow only revealed signs of lighter elements such as hydrogen and helium. Furthering the event’s mystique is the variability of the X-ray emission several days after its discovery, which is a clear sign of an energy source at its centre. Half a year after its discovery, two opposing theories aim to explain these features.

    The first theory states that an unlucky compact object was destroyed when coming too close to a black hole – a phenomenon called a tidal disruption event. The fast increase in brightness excludes normal stars. On the other hand, a smaller object (such as a neutron star, a very dense star consisting of neutron matter) cannot explain the hydrogen and helium observed in the remnant, since it contains no proper elements. The remaining possibility is a white dwarf, a dense star remaining after a normal star has ceased fusion but kept from gravitational collapse into a neutron star or black hole by the electron-degeneracy pressure in its core. The observed emission from the Cow could be explained if a white dwarf was torn apart by tidal forces in the vicinity of a massive black hole. One problem with this theory, however, is the event’s location, since black holes with the sizes required for such an event are normally not found in the spiral arms of galaxies.

    The opposing theory is that the Cow was a special type of supernova in which either a black hole or a quickly rotating highly magnetic neutron star, a magnetar, is produced. While the bright emission in the optical and UV bands are produced by the supernova-like event, the variable X-ray emission is produced by radiating gas falling into the compact object. Normally the debris of a supernova blocks most of the light from reaching us, but the progenitor of the Cow was likely a relatively low-mass star that caused little debris. A hint of its low mass was also found in the X-ray data. If so, the observations would constitute the first observation of the birth of a compact object, making these data very valuable for further theoretical development. Such magnetar sources could also be responsible for ultra-high-energy cosmic rays as well as high-energy neutrinos, two of which might have been observed already. The debate on the nature of the Cow continues, but the wealth of information gathered so far indicates the growing importance of multi-messenger astronomy.

    Further reading

    R Margutti et al. 2018 arXiv:1810.10720.

    K Fang et al. 2018 arXiv:1812.11673.

    N Paul and M Kuin 2018 arXiv:1808.08492.

    See the full article here .


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    Please help promote STEM in your local schools.


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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN/ATLAS detector

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN map

    CERN LHC Grand Tunnel

    CERN LHC particles

     
  • 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!

    If you would like to contact me with suggestions, comments, corrections, errors or new company announcements, please send me an email at rich@insidehpc.com. Or you can send me mail at:

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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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    Penn State Campus

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • 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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    Visit ESO in Social Media-

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    ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre EEuropean Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

    ESO La Silla HELIOS (HARPS Experiment for Light Integrated Over the Sun)

    ESO 3.6m telescope & HARPS at Cerro LaSilla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO 2.2 meter telescope at La Silla, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO/Cerro LaSilla, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO VLT Platform at Cerro Paranal elevation 2,635 m (8,645 ft)


    ESO VLT 4 lasers on Yepun

    Glistening against the awesome backdrop of the night sky above ESO_s Paranal Observatory, four laser beams project out into the darkness from Unit Telescope 4 UT4 of the VLT.

    ESO/NTT at Cerro La Silla, Chile, at an altitude of 2400 metres



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

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

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile. located at the summit of the mountain at an altitude of 3,060 metres (10,040 ft).

    ESO/APEX high on the Chajnantor plateau in Chile’s Atacama region, at an altitude of over 4,800 m (15,700 ft)

    Leiden MASCARA instrument, La Silla, located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    ESO Next Generation Transit Survey at Cerro Paranel, 2,635 metres (8,645 ft) above sea level

    SPECULOOS four 1m-diameter robotic telescopes 2016 in the ESO Paranal Observatory, 2,635 metres (8,645 ft) above sea level

    ESO TAROT telescope at Paranal, 2,635 metres (8,645 ft) above sea level

    ESO ExTrA telescopes at Cerro LaSilla at an altitude of 2400 metres

     
  • 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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    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.

     
  • 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” 

    NASA JPL Banner

    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.

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    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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