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  • richardmitnick 8:14 pm on August 4, 2015 Permalink | Reply
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    From RAS: “5 billion light years across: the largest feature in the universe” 

    Royal Astronomical Society

    Royal Astronomical Society

    04 August 2015

    Media contact
    Dr Robert Massey
    Royal Astronomical Society
    Tel: +44 (0)20 7734 3307
    Mob: +44 (0)794 124 8035
    rm@ras.org.uk

    Science contact
    rof Lajos Balazs
    Konkoly Observatory
    Budapest
    Hungary
    Tel: +36 1 3919354
    lgbalazs@gmail.com

    1
    An image of the distribution of GRBs on the sky at a distance of 7 billion light years, centred on the newly discovered ring. The positions of the GRBs are marked by blue dots and the Milky Way is indicated for reference, running from left to right across the image. Credit: L. Balazs.

    A Hungarian-US team of astronomers have found what appears to be the largest feature in the observable universe: a ring of nine gamma ray bursts [GRB’S] – and hence galaxies – 5 billion light years across. The scientists, led by Prof Lajos Balazs of Konkoly Observatory in Budapest, report their work in a paper in Monthly Notices of the Royal Astronomical Society.

    Gamma-ray bursts (GRBs) are the most luminous events in the universe, releasing as much energy in a few seconds as the Sun does over its 10 billion year lifetime. They are thought to be the result of massive stars collapsing into black holes. Their huge luminosity helps astronomers to map out the location of distant galaxies, something the team exploited.

    The GRBs that make up the newly discovered ring were observed using a variety of space- and ground-based observatories (the sample is listed in the Gamma Ray Burst Online Index). They appear to be at very similar distances from us – around 7 billion light years – in a circle 36° across on the sky, or more than 70 times the diameter of the Full Moon. This implies that the ring is more than 5 billion light years across, and according to Prof Balazs there is only a 1 in 20,000 probability of the GRBs being in this distribution by chance.

    Most current models indicate that the structure of the cosmos is uniform on the largest scales. This ‘Cosmological Principle’ is backed up by observations of the early universe and its microwave background signature, seen by the WMAP and Planck satellites.

    Cosmic Microwave Background WMAP
    CMB per NASA/WMAP

    NASA WMAP
    NASA/WMAP

    Cosmic Background Radiation Planck
    CMB per ESA/Planck

    ESA Planck
    ESA/Planck

    Other recent results and this new discovery challenge the principle, which sets a theoretical limit of 1.2 billion light years for the largest structures. The newly discovered ring is almost five times as large.

    “If the ring represents a real spatial structure, then it has to be seen nearly face-on because of the small variations of GRB distances around the object’s centre. The ring could though instead be a projection of a sphere, where the GRBs all occurred within a 250 million year period, a short timescale compared with the age of the universe.”

    A spheroidal ring projection would mirror the strings of clusters of galaxies seen to surround voids in the universe; voids and string-like formations are seen and predicted by many models of the cosmos. The newly discovered ring is however at least ten times larger than known voids.

    Prof Balazs comments: “If we are right, this structure contradicts the current models of the universe. It was a huge surprise to find something this big – and we still don’t quite understand how it came to exist at all.”

    The team now want to find out more about the ring, and establish whether the known processes for galaxy formation and large scale structure could have led to its creation, or if astronomers need to radically revise their theories of the evolution of the cosmos.

    Further information

    The new work appears in A giant ring-like structure at 0.78 < z < 0.86 displayed by GRBs, Monthly Notices of the Royal Astronomical Society, L. G. Balazs, Z. Bagoly, J. E. Hakkila I. Horvath, J. Kobori, I. R ́acz and L. V. T ́oth, Oxford University Press.

    See the full article here.

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  • richardmitnick 12:27 pm on July 8, 2015 Permalink | Reply
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    From ESO: “Biggest Explosions in the Universe Powered by Strongest Magnets” 


    European Southern Observatory

    8 July 2015
    Jochen Greiner
    Max-Planck Institut für extraterrestrische Physik
    Garching, Germany
    Tel: +49 89 30000 3847
    Email: jcg@mpe.mpg.de

    Richard Hook
    ESO Public Information Officer
    Garching bei München, Germany
    Tel: +49 89 3200 6655
    Cell: +49 151 1537 3591
    Email: rhook@eso.org

    1

    Observations from ESO’s La Silla and Paranal Observatories in Chile have for the first time demonstrated a link between a very long-lasting burst of gamma rays and an unusually bright supernova explosion. The results show that the supernova was not driven by radioactive decay, as expected, but was instead powered by the decaying super-strong magnetic fields around an exotic object called a magnetar. The results will appear in the journal Nature on 9 July 2015.

    Gamma ray bursts (GRBs) are one of the outcomes associated with the biggest explosions to have taken place since the Big Bang. They are detected by orbiting telescopes that are sensitive to this type of high-energy radiation, which cannot penetrate the Earth’s atmosphere, and then observed at longer wavelengths by other telescopes both in space and on the ground.

    GRBs usually only last a few seconds, but in very rare cases the gamma rays continue for hours [1]. One such ultra-long duration GRB was picked up by the Swift satellite on 9 December 2011 and named GRB 111209A. It was both one of the longest and brightest GRBs ever observed.

    NASA SWIFT Telescope
    NASA/Swift

    As the afterglow from this burst faded it was studied using both the GROND instrument on the MPG/ESO 2.2-metre telescope at La Silla and also with the X-shooter instrument on the Very Large Telescope (VLT) at Paranal. The clear signature of a supernova, later named SN 2011kl, was found. This is the first time that a supernova has been found to be associated with an ultra-long GRB [2].

    ESO GROND Instrument
    GROND

    ESO X-shooter
    X-shooter instrument

    The lead author of the new paper, Jochen Greiner from the Max-Planck-Institut für extraterrestrische Physik, Garching, Germany explains: “Since a long-duration gamma-ray burst is produced only once every 10 000–100 000 supernovae, the star that exploded must be somehow special. Astronomers had assumed that these GRBs came from very massive stars — about 50 times the mass of the Sun — and that they signalled the formation of a black hole. But now our new observations of the supernova SN 2011kl, found after the GRB 111209A, are changing this paradigm for ultra-long duration GRBs.”

    In the favoured scenario of a massive star collapse (sometimes known as a Collapsar) the week-long burst of optical/infrared emission from the supernova is expected to come from the decay of radioactive nickel-56 formed in the explosion [3]. But in the case of GRB 111209A the combined GROND and VLT observations showed unambiguously for the first time that this could not be the case [4]. Other suggestions were also ruled out [5].

    The only explanation that fitted the observations of the supernova following GRB 111209A was that it was being powered by a magnetar — a tiny neutron star spinning hundreds of times per second and possessing a magnetic field much stronger than normal neutron stars, which are also known as radio pulsars [6]. Magnetars are thought to be the most strongly magnetised objects in the known Universe. This is the first time that such an unambiguous connection between a supernova and a magnetar has been possible.

    Paolo Mazzali, co-author of the study, reflects on the significance of the new findings: “The new results provide good evidence for an unexpected relation between GRBs, very bright supernovae and magnetars. Some of these connections were already suspected on theoretical grounds for some years, but linking everything together is an exciting new development.”

    “The case of SN 2011kl/GRB 111209A forces us to consider an alternative to the collapsar scenario. This finding brings us much closer to a new and clearer picture of the workings of GRBs,” concludes Jochen Greiner.
    Notes

    [1] Normal long-duration GRBs last between 2 and 2000 seconds. There are now four GRBs known with durations between 10 000–25 000 seconds — these are called ultra-long GRBs. There is also a distinct class of shorter-duration GRBs that are believed to be created by a different mechanism.

    [2] The link between supernovae and (normal) long-duration GRBs was established initially in 1998, mainly by observations at ESO observatories of the supernova SN 1998bw, and confirmed in 2003 with GRB 030329.

    [3] The GRB itself is thought to be powered by the relativistic jets produced by the star’s material collapsing onto the central compact object via a hot, dense accretion disc.

    [4] The amount of nickel-56 measured in the supernova with the GROND instrument is much too large to be compatible with the strong ultraviolet emission as seen with the X-shooter instrument.

    [5] Other suggested sources of energy to explain superluminous supernovae were shock interactions with the surrounding material — possibly linked to stellar shells ejected before the explosion — or a blue supergiant progenitor star. In the case of SN 2011kl the observations clearly exclude both of these options.

    [6] Pulsars make up the most common class of observable neutron stars, but magnetars are thought to develop magnetic field strengths that are 100 to 1000 times greater than those seen in pulsars.
    More information

    This research was presented in a paper entitled “A very luminous magnetar-powered supernova associated with an ultra-long gamma-ray burst”, by J. Greiner et al., to appear in the journal Nature on 9 July 2015.

    The team is composed of Jochen Greiner (Max-Planck-Institut für extraterrestrische Physik, Garching, Germany [MPE]; Excellence Cluster Universe, Technische Universität München, Garching, Germany), Paolo A. Mazzali (Astrophysics Research Institute, Liverpool John Moores University, Liverpool, England; Max-Planck-Institut für Astrophysik, Garching, Germany [MPA]), D. Alexander Kann (Thüringer Landessternwarte Tautenburg, Tautenburg, Germany), Thomas Krühler (ESO, Santiago, Chile) , Elena Pian (INAF, Institute of Space Astrophysics and Cosmic Physics, Bologna, Italy; Scuola Normale Superiore, Pisa, Italy), Simon Prentice (Astrophysics Research Institute, Liverpool John Moores University, Liverpool, England), Felipe Olivares E. (Departamento de Ciencias Fisicas, Universidad Andres Bello, Santiago, Chile), Andrea Rossi (Thüringer Landessternwarte Tautenburg, Tautenburg, Germany; INAF, Institute of Space Astrophysics and Cosmic Physics, Bologna, Italy), Sylvio Klose (Thüringer Landessternwarte Tautenburg, Tautenburg, Germany) , Stefan Taubenberger (MPA; ESO, Garching, Germany), Fabian Knust (MPE), Paulo M.J. Afonso (American River College, Sacramento, California, USA), Chris Ashall (Astrophysics Research Institute, Liverpool John Moores University, Liverpool, England), Jan Bolmer (MPE; Technische Universität München, Garching, Germany), Corentin Delvaux (MPE), Roland Diehl (MPE), Jonathan Elliott (MPE; Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA), Robert Filgas (Institute of Experimental and Applied Physics, Czech Technical University in Prague, Prague, Czech Republic), Johan P.U. Fynbo (DARK Cosmology Center, Niels-Bohr-Institut, University of Copenhagen, Denmark), John F. Graham (MPE), Ana Nicuesa Guelbenzu (Thüringer Landessternwarte Tautenburg, Tautenburg, Germany), Shiho Kobayashi (Astrophysics Research Institute, Liverpool John Moores University, Liverpool, England), Giorgos Leloudas (DARK Cosmology Center, Niels-Bohr-Institut, University of Copenhagen, Denmark; Department of Particle Physics & Astrophysics, Weizmann Institute of Science, Israel), Sandra Savaglio (MPE; Universita della Calabria, Italy), Patricia Schady (MPE), Sebastian Schmidl (Thüringer Landessternwarte Tautenburg, Tautenburg, Germany), Tassilo Schweyer (MPE; Technische Universität München, Garching, Germany), Vladimir Sudilovsky (MPE; Harvard-Smithonian Center for Astrophysics, Cambridge, Massachusetts, USA), Mohit Tanga (MPE), Adria C. Updike (Roger Williams University, Bristol, Rhode Island, USA), Hendrik van Eerten (MPE) and Karla Varela (MPE)..

    See the full article here.

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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 European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

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    VLT Survey Telescope

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  • richardmitnick 10:13 am on May 27, 2015 Permalink | Reply
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    From LLNL: “Lawrence Livermore scientists move one step closer to mimicking gamma-ray bursts” 


    Lawrence Livermore National Laboratory

    May. 26, 2015

    Anne M Stark
    stark8@llnl.gov (link sends e-mail)
    925-422-9799

    1
    The Centaurus A galaxy, at a distance of about 12 million light years from Earth, contains a gargantuan jet blasting away from a central supermassive black hole. In this image, red, green and blue show low, medium and high-energy X-rays. Photo courtesy NASA/CXC/U. Birmingham/M. Burke et al.

    Using ever more energetic lasers, Lawrence Livermore researchers have produced a record high number of electron-positron pairs, opening exciting opportunities to study extreme astrophysical processes, such as black holes and gamma-ray bursts.

    By performing experiments using three laser systems — Titan at Lawrence Livermore, Omega-EP at the Laboratory for Laser Energetics (link is external) and Orion at Atomic Weapons Establishment (link is external) (AWE) in the United Kingdom — LLNL physicist Hui Chen and her colleagues created nearly a trillion positrons (also known as antimatter particles). In previous experiments at the Titan laser in 2008, Chen’s team had created billions of positrons.

    Positrons, or “anti-electrons,” are anti-particles with the same mass as an electron but with opposite charge. The generation of energetic electron-positron pairs is common in extreme astrophysical environments associated with the rapid collapse of stars and formation of black holes. These pairs eventually radiate their energy, producing extremely bright bursts of gamma rays. Gamma-ray bursts (GRBs) are the brightest electromagnetic events known to occur in the universe and can last from ten milliseconds to several minutes. The mechanism of how these GRBs are produced is still a mystery.

    In the laboratory, jets of electron-positron pairs can be generated by shining intense laser light into a gold foil. The interaction produces high-energy radiation that will traverse the material and create electron-positron pairs as it interacts with the nucleus of the gold atoms. The ability to create a large number of positrons in a laboratory, by using energetic lasers, opens the door to several new avenues of antimatter research, including the understanding of the physics underlying extreme astrophysical phenomena such as black holes and gamma-ray bursts.

    “The goal of our experiments was to understand how the flux of electron-positron pairs produced scales with laser energy,” said Chen, who along with former Lawrence Fellow Frederico Fiuza (now at SLAC National Accelerator Laboratory), co-authored the article appearing in the May 18 edition of Physical Review Letters.

    “We have identified the dominant physics associated with the scaling of positron yield with laser and target parameters, and we can now look at its implication for using it to study the physics relevant to gamma-ray bursts,” Chen said. “The favorable scaling of electron-positron pairs with laser energy obtained in our experiments suggests that, at a laser intensity and pulse duration comparable to what is available, near-future 10-kilojoule-class lasers would provide 100 times higher antimatter yield.”

    The team used these scaling results obtained experimentally together with first-principles simulations to model the interaction of two electron positron pairs for future laser parameters. “Our simulations show that with upcoming laser systems, we can study how these energetic pairs of matter-antimatter convert their energy into radiation,” Fiuza said. “Confirming these predictions in an experiment would be extremely exciting.”

    Antimatter research could reveal why more matter than antimatter survived the Big Bang at the start of the universe. There is considerable speculation as to why the observable universe is apparently almost entirely matter, whether other places are almost entirely antimatter, and what might be possible if antimatter could be harnessed. Normal matter and antimatter are thought to have been in balance in the very early universe, but due to an “asymmetry” the antimatter decayed or was annihilated, and today very little antimatter is seen.

    In future work, the researchers plan to use the National Ignition Facility [NIF] to conduct laser antimatter experiments to study the physics of relativistic pair shocks in gamma-ray bursts by creating even higher fluxes of electron-positron pairs.

    LLNL NIF
    NIF

    The research was funded by LLNL’s Laboratory Directed Research and Development program and the LLNL Lawrence Fellowship.

    Chen and Fiuza were joined by Anthony Link, Andy Hazi, Matt Hill, David Hoarty, Steve James, Shaun Kerr, David Meyerhofer, Jason Myatt, Jaebum Park, Yasuhiko Sentoku and Jackson Williams from LLNL, AWE, University of Alberta, University of Rochester and University of Nevada, Reno.

    See the full article here.

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    Operated by Lawrence Livermore National Security, LLC, for the Department of Energy’s National Nuclear Security
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  • richardmitnick 2:38 pm on April 13, 2015 Permalink | Reply
    Tags: , Gamma Ray Bursts,   

    From Penn State: “Inside the most powerful explosions” 

    Penn State Bloc

    Pennsylvania State University

    April 13, 2015
    Barbara K. Kennedy

    1
    In the most common type of gamma-ray burst, illustrated here, a dying massive star forms a black hole (left), which drives a particle jet into space. Light across the spectrum arises from hot gas near the progenitor star, from collisions within the jet, and through the jet’s interaction with its surroundings.
    Image: NASA Goddard Space Flight Center

    New research by an international team that includes Penn State University scientists provides new information about what can happen inside the gigantic bursts of gamma rays that are produced by the catastrophic death of extremely massive stars — the most powerful explosions in the universe. The research has enabled the scientists to begin solving the mystery of whether these gamma ray bursts are the source of extremely high-energy cosmic rays and neutrinos that bombard Earth as astroparticles from space.

    The team’s achievement is based on their construction of some of the most sophisticated computational calculations ever that take into account detailed microphysical processes as well as the complex internal structure of gamma ray bursts. The team’s simulations show that emission of the different kinds of astroparticles should be a key to understanding the roles of gamma-ray bursts as extreme particle accelerators. The study also raises new questions that can be answered by next-generation telescopes for the detection of neutrinos and gamma rays. The research will be published online on April 10, 2015, in the journal Nature Communications.

    “Gamma ray bursts, the brightest explosive phenomena in the universe, are promising accelerators of very-high-energy particles, with energies much higher than those our current technology can achieve on the Earth,” said Kohta Murase, assistant professor of physics and astronomy and astrophysics at Penn State, a coauthor of the Nature Communications paper along with other scientists from Penn State, Ohio State University, and the DESY national research center in Germany. “Prompt gamma rays are radiated from a relativistic jet, which shoots out into space at velocities that are about 99.9995 percent of the speed of light, leaving behind a newborn black hole or neutron star as a remnant of the massive explosion.”

    A gamma ray burst’s jets form when a dying massive star collapses, and powerful plasma streams penetrate their progenitor star through both of its poles. A good fraction of the jets’ energy is converted into energetic particles including gamma rays and neutrinos, which travel far out into space, sometimes for about ten billion light years before reaching Earth. With the new computer calculation built by the research team, the scientists have been able to model details of the production of the very-high-energy astroparticles inside the gamma ray burst’s jets.

    The scientists say that this new study is a natural outgrowth of recent findings in astroparticle physics, including the first confirmed cosmic neutrinos detected at the IceCube Neutrino Observatory at the South Pole in 2013. Penn State scientists contributed to this previous discovery.

    ICECUBE neutrino detector
    IceCube neutrino detector interior
    IceCube

    “Previously, the details of the inhomogeneity of the gamma ray burst jets were not too important in our models, and that was a totally valid assumption — up until IceCube saw the first cosmic neutrinos a couple of years ago,” said Mauricio Bustamante, a Fellow of the Center for Cosmology and AstroParticle Physics at Ohio State and a coauthor of the Nature Communications paper. “Now that we have seen them, we can start excluding some of our initial predictions, and we decided to go one step further and do this kind of analysis.”

    The scientists have developed clever techniques to treat the generation and fate of high-energy particles in detail. They wrote new computer code to take into account the shock waves that are likely to occur within the jets. They simulated what would happen when shells of plasma in the jets collided. And they calculated the particle production in each region. In this internal-shock model, some regions of the jet are denser than others, and some plasma shells travel faster than others — like a long highway where the cars are traveling at different speeds. In the gamma ray burst jets, however, the particles are traveling at close to the speed of light.

    When these plasma shells collide, they create debris consisting of energetic particles, plus turbulent magnetic fields. “The debris contains neutrinos, cosmic rays, and gamma rays, but, depending on where the collisions occurred, one of these typically will dominate the emission,” Bustamante said. The team’s new calculation shows that, in the internal-shock model, neutrinos largely originate from internal collisions that occur closest to the engine of the gamma ray burst, where the concentration of particles is higher; collisions that occur far away will mostly produce the gamma rays that we detect on Earth; and cosmic-ray protons are mostly released from collisions at intermediate distances from the engine.

    The research team’s findings support some ideas developed by Murase, who previously showed the importance of the innermost collisions for the emission of neutrinos. Murase and his collaborators also had suggested that heavier elements like oxygen and iron can be accelerated and emitted as extremely high-energy cosmic rays only if collisions occur sufficiently far away from the engine of the gamma ray burst. The team’s new calculation also implies that the amount of neutrinos that reach the Earth is below the detection threshold that can be achieved by today’s neutrino telescopes such as IceCube.

    “We have found a non-trivial new effect that was not shown in any previous work,” Murase said. “Since our predicted fluxes are more robust than previous expectations, our study enhances the feasibility of testing the hypothesis that extremely high-energy cosmic rays come from gamma ray bursts.” When the next generation of neutrino and gamma ray telescopes begin operating, astrophysicists can use this new calculation to refine notions of gamma ray bursts as particle accelerators, and to better understand the sources of extremely high-energy cosmic particles detected on Earth.

    In addition to Murase and Bustamante, other co-authors of the paper are Philipp Baerwald at Penn State and Walter Winter at DESY in Germany. This work was funded by NASA, the German Research Foundation, and the U.S. National Science Foundation.”

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  • richardmitnick 9:09 am on April 10, 2015 Permalink | Reply
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    From DESY: “Gamma-ray bursts as cosmic particle accelerators” 

    DESY
    DESY

    2015/04/10
    No Writer Credit

    1

    Study provides new insights into the universe’s most powerful explosions

    A new study provides detailed insight into the most powerful explosions in the universe: gamma-ray bursts. The simulation explains the modes of particle acceleration in these rare events better than previous models and can explain conflicting astrophysical observations. Scientists from DESY and two US universites present their work in the journal Nature Communications.

    Gamma-ray bursts happen when extremely massive stars go supernova. These explosions can be seen nearly across the whole visible universe, up to several billion lightyears. The giant stars’ strong magnetic fields channel most of the explosion’s energy into two powerful jets of electrically charged gas (plasma), one at each magnetic pole. These plasma jets are powerful natural particle accelerators.

    Scientists expect the plasma jets to be a significant source of cosmic rays, high-energy subatomic particles (mostly protons) that constantly pepper Earth’s atmosphere from space. These particles can have up to ten million times the energy of the protons in the Large Hadron Collider (LHC), currently the most powerful particle accelerator on Earth at the European particle physics laboratory CERN.

    But if gamma-ray bursts are a significant source of cosmic rays, scientists expect them for physics reasons to also shed a large number of light elementary particles called neutrinos. The IceCube observatory at the South Pole, in which DESY is the main European partner, is looking for exactly those high-energy cosmic neutrinos.

    ICECUBE neutrino detector
    IceCube neutrino detector interior
    IceCube

    However, none have been detected so far from gamma-ray bursts. This means that at least ten times fewer neutrinos reach us from gamma-ray bursts than were expected. “This throws up new questions for theory,” says DESY scientist Walter Winter, a co-author of the new study. “Perhaps, our concept of gamma-ray bursts was too simple.”

    2
    The plasma is ejected in shells at different speeds. When the shells collide, particles are accelerated. Illustration: Mauricio Bustamante/DESY

    3
    Neutrinos are mainly generated at lower distance from the source, cosmic rays at medium distance and gamma-rays at greater distance. Illustration Mauricio Bustamante/DESY

    Existing models of these powerful explosions assumed that cosmic rays, neutrinos and gamma-rays all come from the same region within the plasma jets. The team of theoretical astroparticle physicists, including Winter from DESY, Mauricio Bustamante from Ohio State University and Philipp Baerwald and Kohta Murase from Pennsylvania State University, has now developed a more dynamic model of gamma-ray bursts. According to this model, the plasma is ejected in the form of shells at different speed. In considerable distance from the source, these shells collide, thereby accelerating particles.

    This approach can not only explain the observed strong variations in the light curves of gamma-ray bursts. A consequence of this model is also that neutrinos, cosmic rays and gamma-rays must be produced in completely different regions of the jets. This can explain, why the expected flux of neutrinos could not be found. “We expect that the next generation of neutrino telescopes, such as IceCube-Gen-2, will be sensitive to this minimal flux that we’re predicting”, says Bustamante. In contrast to earlier models, this estimate is more robust and does only weakly depend on the characteristics of individual gamma-ray bursts.

    Reference:
    Neutrino and Csomic-Ray Emission from Multiple Internal Shocks In Gamma-Ray Bursts; Mauricio Bustamante, Philipp Baerwald, Kohta Murase & Walter Winter; „Nature Communications“, 2015; DOI: 10.1038/ncomms7783

    See the full article here.

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    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

     
  • richardmitnick 5:45 pm on December 9, 2014 Permalink | Reply
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    From blueshift: “Happy Birthday, Swift!” 

    NASA Blueshift
    NASA Blueshift

    December 9, 2014
    Maggie Masetti

    This is our third Happy Birthday post for a satellite in the last year or so – which is pretty cool actually, to have satellites that are hitting significant milestones and have had the longevity to still be doing great science. We had Fermi’s 5th birthday in August 2013, followed by Spitzer’s 10th in September 2013.

    NASA Fermi Telescope
    NASA/Fermi

    NASA Spitzer Telescope
    NASA/Spitzer

    And then we just recently hit Swift’s 10th birthday. What is Swift? Swift is an observatory that has been dedicated to studying gamma-ray bursts (GRBs) – and it can study GRBs and their afterglows at gamma ray, X-ray, ultraviolet, and optical wavelengths.

    NASA SWIFT Telescope
    NASA/Swift

    GRBs are short-lived bursts of gamma-ray light, which can last from few milliseconds to several minutes, and shine hundreds of times brighter than a typical supernova and about a million trillion times as bright as our Sun. Furthermore, when a GRB erupts, it is briefly the brightest source of cosmic gamma ray photons in the observable Universe. (Thanks to Imagine the Universe!, more info there.) What exactly was causing these incredibly energetic bursts was a big mystery. Enter Swift. Data from Swift (and also the gamma-ray Fermi observatory) have given us valuable clues that are helping us solve this mystery. (We got the scoop on the latest in the interview you’ll see below.

    We actually built Swift here at NASA Goddard. I was fortunate enough to get the chance to see the satellite before it launched. They displayed it in its cleanroom. Here is me 10 years ago with Brendan, Steve, and Meredith. (Meredith and Steve have been a huge help to Blueshift behind the scenes on the server side of things.)
    m

    s
    With Swift

    Sara and I talked to the Principal Investigator for the Swift mission, Neil Gehrels, to ask him 10 questions about Swift for its 10th Anniversary.

    Blueshift: What is your role with Swift? How long have you been involved with the project?

    Neil Gehrels: I am the lead scientist of Swift. In NASA jargon, my role is Principal Investigator. My involvement started at the very beginning in 1996 when Nick White and I conceived of the mission.

    Blueshift: How did Swift come to be?

    Neil Gehrels: NASA has competitions every other year for small to medium sized missions. Typically 40 teams put in proposals and one is chosen to fly through a rigorous and grueling peer review process. We proposed Swift in 1998 and were fortunate enough to have it selected. The observatory was constructed from 1999 to 2004 and then launched.

    Blueshift: Were you at the launch? What was it like to watch Swift head into space?

    Neil Gehrels: Yes, I was in the control center at the launch. It was one of the most exciting days of my life. Exhilaration mixed with fear of failure! Luckily everything went perfectly.

    Blueshift: Why gamma rays? What are they, and what do they tell us about the Universe?

    Neil Gehrels: Gamma rays are like really powerful X-rays. Just like the X-rays at the dentist office, they are very penetrating rays of light. The are produced in the hottest, most explosive events in the universe. We use them to study the death of stars and birth of black holes.

    Blueshift: What’s Swift’s role within the international fleet of astrophysics satellites?

    Neil Gehrels: Swift is the NASA’s premier satellite for observing the most explosive and dynamic sources in the universe. Objects such as gamma-ray bursts and supernovae. The observatory detects the transient sources and then repoints itself, without human intervention, at the source for detailed observations with the on-board telescopes

    Blueshift: What research have you personally done with Swift?

    Neil Gehrels: My personal research is studying gamma-ray bursts. Whenever one is detected by Swift, which occurs about twice per week, I receive a text message on my phone and run to the nearest computer to look at the new data.

    Blueshift: Did you expect to still be doing amazing science with Swift ten years later?

    Neil Gehrels: Swift was built to operate for 2 years, but hoped it would go much longer. It is such a joy to have it still working perfectly after ten years.

    Blueshift: Has Swift helped provide answers to major astronomical mysteries such as the cause of gamma-ray bursts?

    Neil Gehrels: Yes, Swift has made major discoveries every year. We found out that long and short gamma-ray bursts have very different origins. Long bursts are from exploding stars and short bursts are from the collision of compact neutron stars. Another big finding was the detection of 2 gamma-ray bursts from the very distant edges of the universe. They were produced in the explosions of very early stars.

    Blueshift: What do you think are the top discoveries made by Swift over the last decade?

    Neil Gehrels: In addition to the major discoveries about gamma-ray bursts, another biggie was detecting a the shredding of a star by a massive black hole. The star drifted too close to the black hole and was torn apart by the strong gravity of the black hole. Another fun discovery was a flash of X-rays from a new supernova explosion. We were lucky to be looking in the direction of a new supernova at the time the star first collapsed and discovered a brilliant pulse of X-rays. It was the long-predict “shock break-out” where a wave of heat zooms through the star at the moment of collapse and bursts out of the surface.

    Blueshift: What’s next for Swift?

    Neil Gehrels: Hopefully Swift will last another 10 years. We are using it in a new way lately, as a resource for astronomers. Our colleagues send an alert to us when they find something interesting going on in the universe and we point Swift at it.

    Blueshift:Thanks!

    And happy birthday to Swift, we hope you have many more!

    c
    The cake from Swift’s birthday party. Credit: Maggie Masetti

    See the full article, with animation, here.

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    Blueshift is produced by a team of contributors in the Astrophysics Science Division at Goddard. Started in 2007, Blueshift came from our desire to make the fascinating stuff going on here every day accessible to the outside world.

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  • richardmitnick 5:30 pm on December 8, 2014 Permalink | Reply
    Tags: , , , , Gamma Ray Bursts, ,   

    From SPACE.com: “Did Deadly Gamma-Ray Burst Cause a Mass Extinction on Earth?” 

    space-dot-com logo

    SPACE.com

    December 08, 2014
    Charles Q. Choi

    A gamma-ray burst, the most powerful kind of explosion known in the universe, may have triggered a mass extinction on Earth within the past billion years, researchers say.

    grb
    In this illustration, a jet is produced by an unusually bright gamma-ray burst.
    Credit: NASA/Swift/Cruz deWilde

    These deadly outbursts could help explain the so-called Fermi paradox, the seeming contradiction between the high chance of alien life and the lack of evidence for it, scientists added.

    Gamma-ray bursts are brief, intense explosions of high-frequency electromagnetic radiation. These outbursts give off as much energy as the sun during its entire 10-billion-year lifetime in anywhere from milliseconds to minutes. Scientists think gamma-ray bursts may be caused by giant exploding stars known as hypernovas, or by collisions between pairs of dead stars known as neutron stars.

    ns
    The pulsar PSR B1509-58, a rapidly spinning neutron star (X-rays from Chandra are gold; Infrared from WISE in red, green and blue/max)
    When an image from NASA’s Chandra X-ray Observatory of PSR B1509-58 — a spinning neutron star surrounded by a cloud of energetic particles –was released in 2009, it quickly gained attention because many saw a hand-like structure in the X-ray emission. In a new image of the system, X-rays from Chandra in gold are seen along with infrared data from NASA’s Wide-field Infrared Survey Explorer (WISE) telescope in red, green and blue. Pareidolia may strike again as some people report seeing a shape of a face.
    NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, also took a picture of the neutron star nebula in 2014, using higher-energy X-rays than Chandra.

    NASA Chandra Telescope
    NASA/Chandra

    NASA Wise Telescope
    NASA/WISE

    NASA NuSTAR
    NASA/NuSTAR

    PSR B1509-58 is about 17,000 light-years from Earth.

    JPL, a division of the California Institute of Technology in Pasadena, manages the WISE mission for NASA. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra’s science and flight operations.

    If a gamma-ray burst exploded within the Milky Way, it could wreak extraordinary havoc if it were pointed directly at Earth, even from thousands of light-years away. Although gamma rays would not penetrate Earth’s atmosphere well enough to burn the ground, they would chemically damage the atmosphere, depleting the ozone layer that protects the planet from damaging ultraviolet rays that could trigger mass extinctions. It’s also possible that gamma-ray bursts may spew out cosmic rays, which are high-energy particles that may create an experience similar to a nuclear explosion for those on the side of the Earth facing the explosion, causing radiation sickness.

    To see how great a threat gamma-ray bursts might pose to Earth, researchers investigated how likely it was that such an explosion could have inflicted damage on the planet in the past.

    Gamma-ray bursts are traditionally divided into two groups — long and short — depending on whether they last more or less than 2 seconds. Long gamma-ray bursts are associated with the deaths of massive stars, while short gamma-ray bursts are most likely caused by the mergers of neutron stars.

    For the most part, long gamma-ray bursts happen in galaxies very different from the Milky Way — dwarf galaxies low in any element heavier than hydrogen and helium. Any long gamma-ray bursts in the Milky Way will likely be confined in regions of the galaxy that are similarly low in any element heavier than hydrogen and helium, the researchers said.

    The scientists discovered the chance that a long gamma-ray burst could trigger mass extinctions on Earth was 50 percent in the past 500 million years, 60 percent in the past 1 billion years, and more than 90 percent in the past 5 billion years. For comparison, the solar system is about 4.6 billion years old.

    Short gamma-ray bursts happen about five times more often than long ones. However, since these shorter bursts are weaker, the researchers found they had negligible life-threatening effects on Earth. They also calculated that gamma-ray bursts from galaxies outside the Milky Way probably pose no threat to Earth.

    These findings suggest that a nearby gamma-ray burst may have caused one of the five greatest mass extinctions on Earth, such as the Ordovician extinction that occurred 440 million years ago. The Ordovician extinction was the earliest of the so-called Big Five extinction events, and is thought by many to be the second largest.

    The scientists also investigated the danger that gamma-ray bursts may pose for life elsewhere in the Milky Way. Stars are packed more densely together toward the center of the galaxy, meaning worlds there face a greater danger of gamma-ray bursts. Worlds in the region about 6,500 light-years around the Milky Way’s core, where 25 percent of the galaxy’s stars reside, faced more than a 95 percent chance of a lethal gamma-ray burst within the past billion years. The researchers suggest that life as it is known on Earth could survive with certainty only in the outskirts of the Milky Way, more than 32,600 light-years from the galactic core.

    The researchers also explored the danger gamma-ray bursts could pose for the universe as a whole. They suggest that because of gamma-ray bursts, life as it is known on Earth might safely develop in only 10 percent of galaxies. They also suggest that such life could only have developed in the past 5 billion years. Before then, galaxies were smaller in size, and gamma-ray bursts were therefore always close enough to cause mass extinctions to any potentially life-harboring planets.

    “This may be an explanation, or at least a partial one, to what is called the Fermi paradox or the ‘Big Silence,'” said lead study author Tsvi Piran, a physicist at the Hebrew University in Jerusalem. “Why we haven’t encountered advanced civilizations so far? The Milky Way galaxy is much older than the solar system and there was ample time and ample space — the number of planetary systems with conditions similar to Earth is huge — for life to develop elsewhere in the galaxy. So why we haven’t encountered advanced civilizations so far?”

    The answer to Fermi’s paradox may be that gamma-ray bursts have struck many life-harboring planets. The most severe criticism of these estimates “is that we address life as we know it on Earth,” Piran told Live Science. “One can imagine very different forms of life that are resilient to the relevant radiation.”

    Piran and his colleague, Raul Jimenez, detailed their findings online today (Dec. 5) in the journal Physical Review Letters.

    See the full article here.

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  • richardmitnick 11:24 am on November 25, 2014 Permalink | Reply
    Tags: , , , , , Gamma Ray Bursts,   

    From AAAS: “Complex life may be possible in only 10% of all galaxies” 

    AAAS

    AAAS

    24 November 2014
    Adrian Cho

    The universe may be a lonelier place than previously thought. Of the estimated 100 billion galaxies in the observable universe, only one in 10 can support complex life like that on Earth, a pair of astrophysicists argues. Everywhere else, stellar explosions known as gamma ray bursts would regularly wipe out any life forms more elaborate than microbes. The detonations also kept the universe lifeless for billions of years after the big bang, the researchers say.

    “It’s kind of surprising that we can have life only in 10% of galaxies and only after 5 billion years,” says Brian Thomas, a physicist at Washburn University in Topeka who was not involved in the work. But “my overall impression is that they are probably right” within the uncertainties in a key parameter in the analysis.

    Scientists have long mused over whether a gamma ray burst could harm Earth. The bursts were discovered in 1967 by satellites designed to spot nuclear weapons tests and now turn up at a rate of about one a day. They come in two types. Short gamma ray bursts last less than a second or two; they most likely occur when two neutron stars or black holes spiral into each other. Long gamma ray bursts last for tens of seconds and occur when massive stars burn out, collapse, and explode. They are rarer than the short ones but release roughly 100 times as much energy. A long burst can outshine the rest of the universe in gamma rays, which are highly energetic photons.

    That seconds-long flash of radiation itself wouldn’t blast away life on a nearby planet. Rather, if the explosion were close enough, the gamma rays would set off a chain of chemical reactions that would destroy the ozone layer in a planet’s atmosphere. With that protective gas gone, deadly ultraviolet radiation from a planet’s sun would rain down for months or years—long enough to cause a mass die-off.

    How likely is that to happen? Tsvi Piran, a theoretical astrophysicist at the Hebrew University of Jerusalem, and Raul Jimenez, a theoretical astrophysicist at the University of Barcelona in Spain, explore that apocalyptic scenario in a paper in press at Physical Review Letters.

    Astrophysicists once thought gamma ray bursts would be most common in regions of galaxies where stars are forming rapidly from gas clouds. But recent data show that the picture is more complex: Long bursts occur mainly in star-forming regions with relatively low levels of elements heavier than hydrogen and helium—low in “metallicity,” in astronomers’ jargon.

    Using the average metallicity and the rough distribution of stars in our Milky Way galaxy, Piran and Jimenez estimate the rates for long and short bursts across the galaxy. They find that the more-energetic long bursts are the real killers and that the chance Earth has been exposed to a lethal blast in the past billion years is about 50%. Some astrophysicists have suggested a gamma ray burst may have caused the Ordovician extinction, a global cataclysm about 450 million years ago that wiped out 80% of Earth’s species, Piran notes.

    The researchers then estimate how badly a planet would get fried in different parts of the galaxy. The sheer density of stars in the middle of the galaxy ensures that planets within about 6500 light-years of the galactic center have a greater than 95% chance of having suffered a lethal gamma ray blast in the last billion years, they find. Generally, they conclude, life is possible only in the outer regions of large galaxies. (Our own solar system is about 27,000 light-years from the center.)

    Things are even bleaker in other galaxies, the researchers report. Compared with the Milky Way, most galaxies are small and low in metallicity. As a result, 90% of them should have too many long gamma ray bursts to sustain life, they argue. What’s more, for about 5 billion years after the big bang, all galaxies were like that, so long gamma ray bursts would have made life impossible anywhere.

    But are 90% of the galaxies barren? That may be going too far, Thomas says. The radiation exposures Piran and Jimenez talk about would do great damage, but they likely wouldn’t snuff out every microbe, he contends. “Completely wiping out life?” he says. “Maybe not.” But Piran says the real issue is the existence of life with the potential for intelligence. “It’s almost certain that bacteria and lower forms of life could survive such an event,” he acknowledges. “But [for more complex life] it would be like hitting a reset button. You’d have to start over from scratch.”

    The analysis could have practical implications for the search for life on other planets, Piran says. For decades, scientists with the SETI Institute in Mountain View, California, have used radio telescopes to search for signals from intelligent life on planets around distant stars. But SETI researchers are looking mostly toward the center of the Milky Way, where the stars are more abundant, Piran says. That’s precisely where gamma ray bursts may make intelligent life impossible, he says: “We are saying maybe you should look in the exact opposite direction.”

    Allen Telescope Array
    Allen Telescope Array, part of SETI Institute

    Arecibo
    Arecibo Radio Telescope used by SETI@home

    NRAO GBT
    NRAO Green Bank Radio Telescope

    Jodrell Bank Lovell Telescope
    Jodrell Bank Lovell Radio Telescope

    See the full article here.

    The American Association for the Advancement of Science is an international non-profit organization dedicated to advancing science for the benefit of all people.

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