Tagged: Gamma Ray Bursts Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 6:56 pm on March 7, 2016 Permalink | Reply
    Tags: , , Gamma Ray Bursts,   

    From phys.org: “Death by gamma-ray bursts may place first lower bound on the cosmological constant” 

    physdotorg
    phys.org

    March 7, 2016
    Lisa Zyga

    Gamma ray burst artist depiction Credit NASA Swift Mary Pat Hrybyk-Keith and John Jones
    Artists’ depiction of a gamma-ray burst. Credit NASA/Swift Mary Pat Hrybyk-Keith and John Jones

    Sometimes when a star collapses into a supernova, it releases an intense, narrow beam of gamma rays. Gamma-ray bursts often last just a few seconds, but during that time they can release as much energy as the Sun will produce in its entire lifetime, making gamma-ray bursts the most powerful explosions ever observed in the universe. They are so intense that, if pointed at the Earth from even the most distant edge of our galaxy, they could easily cause a mass extinction, possibly obliterating all life on the planet. It’s thought that a gamma-ray burst may have caused the Ordovician extinction around 440 million years ago, which wiped out 85% of all species at the time.

    Clearly, the farther away a planet is from gamma-ray bursts, the better its chances of harboring advanced forms of life. In a new paper, scientists have shown that the gamma-ray burst risk to life favors a universe where all objects (like planets and gamma-ray bursts) are relatively far apart. And the main factor that tells how far apart everything is in the universe—or in other words, how things are spreading out and moving away from each other—is dark energy or the cosmological constant.

    One of the biggest unanswered questions in cosmology is why does the cosmological constant have the particular value that scientists observe? Einstein initially devised the cosmological constant to be like an “anti-gravity” force, so that a larger value means that the universe is expanding very rapidly and objects are being pushed farther apart from each other. A smaller value means that the universe itself is smaller and objects are somewhat closer together.

    Currently, the value of the cosmological constant is estimated to be about 10^-123. Researchers have placed upper bounds on this value (it can’t be more than 10^-120 or else galaxies and other structures could not form because their matter could not have gotten close enough together). But so far, no research has been able to place a lower bound on the value.

    By showing that the chances of advanced life existing is extremely small when planets are close to gamma-ray bursts, the new study makes an argument for placing the first lower bounds on the value of the cosmological constant. The scientists estimate that, when the value gets below 10^-124, the number of protective “halos” of space (regions where planets stand a chance of avoiding gamma-ray bursts for long periods of time) sharply decreases. In other words, it would be pretty unlikely for humans to exist if the value were smaller than this number.

    “We have found a lower limit on the cosmological constant,” coauthor Tsvi Piran at The Hebrew University in Jerusalem told Phys.org. “As you know it is very small, 10^-123. If it is so small, then why not zero? Zero is a ’round’ number and one can look for a basic law of physics that will force the cosmological constant to vanish. Additionally, why not a negative value?”

    By showing that the cosmological constant is very unlikely to be zero or negative, and much more likely to be close to its observed value, the results may help explain where this value comes from.

    “This is important as it gives clues to the question of what is the origin of this constant,” Piran said. “It is generally believed that the value of the cosmological constant is determined by some quantum process, and understanding its relevant range is important to have a clue on its origin.”

    The full analysis is more complicated, as the researchers had to account for other factors, such as the age of the universe—it can’t be too young nor too old for advanced life. It can’t be too old because planets need to orbit around a hydrogen-burning star like our Sun, which is young enough that it has not yet reached the end of its lifetime. But the universe also can’t be too young because a galaxy (where protective halos reside) must have time to undergo chemical evolution to produce metal elements. A high metallicity decreases the odds of having a nearby gamma-ray burst, since the stars that cause these bursts have relatively low metal concentrations.

    It’s not surprising that Earth seems to occupy a favorable point in the researchers’ simulations: a place with minimal exposure to gamma-ray bursts, and at a time with many hydrogen-burning stars like the Sun, along with a high average metallicity. This special place and time may help researchers search for other possible locations of life in the universe.

    “We would like to further refine this limit and extend the range of parameters (beyond just the cosmological constant) that influence the rate of gamma-ray bursts, and investigate their implications for the possible locations of planets that can harbor life,” Piran said.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

    Advertisements
     
  • richardmitnick 9:59 pm on February 23, 2016 Permalink | Reply
    Tags: , , , Gamma Ray Bursts,   

    From CfA: “LIGO’s Twin Black Holes Might Have Been Born Inside a Single Star” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    February 23, 2016
    Christine Pulliam
    Media Relations Manager
    Harvard-Smithsonian Center for Astrophysics
    617-495-7463
    cpulliam@cfa.harvard.edu

    Black holes merging Astronomy.com
    An artist’s impression of two black holes orbiting each other, generating gravitational waves. Swinburne Astronomy Productions

    On September 14, 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves from the merger of two black holes 29 and 36 times the mass of the Sun.

    Caltech Ligo
    MIT/Caltech Advanced aLIGO

    Such an event is expected to be dark, but the Fermi Space Telescope detected a gamma-ray burst just a fraction of a second after LIGO’s signal. New research suggests that the two black holes might have resided inside a single, massive star whose death generated the gamma-ray burst.

    NASA Fermi Telescope
    NASA/Fermi

    “It’s the cosmic equivalent of a pregnant woman carrying twins inside her belly,” says Harvard astrophysicist Avi Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA).

    Normally, when a massive star reaches the end of its life, its core collapses into a single black hole. But if the star was spinning very rapidly, its core might stretch into a dumbbell shape and fragment into two clumps, each forming its own black hole.

    A very massive star as needed here often forms out of the merger of two smaller stars. And since the stars would have revolved around each other faster and faster as they spiraled together, the resulting merged star would be expected to spin very quickly.

    After the black hole pair formed, the star’s outer envelope rushed inward toward them. In order to power both the gravitational wave event and the gamma-ray burst, the twin black holes must have been born close together, with an initial separation of order the size of the Earth, and merged within minutes.

    Cornell SXS teamTwo merging black holes simulation
    Merging black holes. Cornell SxS team

    The newly formed single black hole then fed on the infalling matter, consuming up to a Sun’s worth of material every second and powering jets of matter that blasted outward to create the burst.

    Fermi detected the burst just 0.4 seconds after LIGO detected gravitational waves, and from the same general area of the sky. However, the [ESA] INTEGRAL gamma-ray satellite did not confirm the signal.

    ESA Integral
    ESA/INTEGRAL

    “Even if the Fermi detection is a false alarm, future LIGO events should be monitored for accompanying light irrespective of whether they originate from black hole mergers. Nature can always surprise us,” says Loeb.

    If more gamma-ray bursts are detected from gravitational wave events, they will offer a promising new method of measuring cosmic distances and the expansion of the universe. By spotting the afterglow of a gamma-ray burst and measuring its redshift, then comparing it to the independent distance measurement from LIGO, astronomers can precisely constrain the cosmological parameters. “Astrophysical black holes are much simpler than other distance indicators, such as supernovae, since they are fully defined just by their mass and spin,” says Loeb.

    “This is an agenda-setting paper that will likely stimulate vigorous follow-up work, in the crucial period after the initial LIGO discovery, where the challenge is to fathom its full implications. If history is any guide, the ‘multi-messenger’ approach advocated by Loeb, using both gravitational waves and electromagnetic radiation, again promises deeper insight into the physical nature of the remarkable LIGO source,” says Volker Bromm of the University of Texas at Austin, commenting independently.

    This research has been accepted for publication in The Astrophysical Journal Letters and is available online.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 8:18 am on November 8, 2015 Permalink | Reply
    Tags: , Gamma Ray Bursts,   

    From NASA Swift: “NASA’s Swift Spots its Thousandth Gamma-ray Burst” 

    NASA Swift Banner

    NASA SWIFT Telescope

    NASA Swift

    Nov. 6, 2015
    Francis Reddy
    NASA’s Goddard Space Flight Center, Greenbelt, Maryland

    1
    GRB 151027B, Swift’s 1,000th burst (center), is shown in this composite X-ray, ultraviolet and optical image. X-rays were captured by Swift’s X-Ray Telescope, which began observing the field 3.4 minutes after the Burst Alert Telescope detected the blast. Swift’s Ultraviolet/Optical Telescope (UVOT) began observations seven seconds later and faintly detected the burst in visible light. The image includes X-rays with energies from 300 to 6,000 electron volts, primarily from the burst, and lower-energy light seen through the UVOT’s visible, blue and ultraviolet filters (shown, respectively, in red, green and blue). The image has a cumulative exposure of 10.4 hours. Credits: NASA/Swift/Phil Evans, Univ. of Leicester

    NASA’s Swift spacecraft has detected its 1,000th gamma-ray burst (GRB). GRBs are the most powerful explosions in the universe, typically associated with the collapse of a massive star and the birth of a black hole.

    “Detecting GRBs is Swift’s bread and butter, and we’re now at 1,000 and counting,” said Neil Gehrels, the Swift principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The spacecraft remains in great shape after nearly 11 years in space, and we expect to see many more GRBs to come.”

    A GRB is a fleeting blast of high-energy light, often lasting a minute or less, occurring somewhere in the sky every couple of days. Scientists are looking for exceptional bursts that offer the deepest insights into the extreme physical processes at work.

    2
    This illustration shows the ingredients of the most common type of gamma-ray burst. The core of a massive star (left) has collapsed, forming a black hole that sends a jet moving through the collapsing star and out into space at near the speed of light. Radiation across the spectrum arises from hot ionized gas in the vicinity of the newborn black hole, collisions among shells of fast-moving gas within the jet, and from the leading edge of the jet as it sweeps up and interacts with its surroundings. Credits: NASA’s Goddard Space Flight Center

    Shortly before 6:41 p.m. EDT on Oct. 27, Swift’s Burst Alert Telescope detected the 1,000th GRB as a sudden pulse of gamma rays arising from a location toward the constellation Eridanus. Astronomers dubbed the event GRB 151027B, after the detection date and the fact that it was the second burst of the day. Swift automatically determined its location, broadcast the position to astronomers around the world, and turned to investigate the source with its own sensitive X-ray, ultraviolet and optical telescopes.

    Astronomers classify GRBs by their duration. Like GRB 151027B, roughly 90 percent of bursts are of the “long” variety, where the gamma-ray pulse lasts more than two seconds. They are believed to occur in a massive star whose core has run out of fuel and collapsed into a black hole. As matter falls toward the newly formed black hole, it launches jets of subatomic particles that move out through the star’s outer layers at nearly the speed of light. When the particle jets reach the stellar surface, they emit gamma rays, the most energetic form of light. In many cases, the star is later seen to explode as a supernova.

    “Short” bursts last less than two seconds — and sometimes just thousandths of a second. Swift observations provide strong evidence these events are caused by mergers of orbiting neutron stars or black holes.

    Once a GRB is identified, the race is on to observe its fading light with as many instruments as possible. Based on alerts from Swift, robotic observatories and human-operated telescopes turn to the blast site to measure its rapidly fading afterglow, which emits X-rays, ultraviolet, visible and infrared light, and radio waves. While optical afterglows are generally faint, they can briefly become bright enough to be seen with the unaided eye.

    “Over the years, astronomers have constantly refined their techniques to get their telescopes onto the burst site in the shortest possible time,” said John Nousek, Swift’s director of mission operations and a professor of astronomy and astrophysics at Penn State University in University Park, Pennsylvania. “In fact, the process to follow up Swift GRB alerts is as productive as ever.”

    GRB 151027B provides a perfect example. Five hours after the Swift alert, the burst location first became visible from the European Southern Observatory (ESO) in Paranal, Chile. There a team led by Dong Xu of the Chinese National Astronomical Observatories in Beijing captured the afterglow’s visible light using the Very Large Telescope’s X-shooter spectrograph. The ESO observations show that light from the burst had been traveling to us for more than 12 billion years, placing it in the most distant few percent of GRBs Swift has recorded.

    ESO VLT Interferometer
    ESO/VLT

    ESO X-shooter
    Very Large Telescope’s X-shooter spectrograph

    Astronomers now have distance measurements for about 30 percent of Swift GRBs, which makes it possible to investigate how these powerful events are distributed across space and time. The distance record is held by GRB 090429B, which exploded at the dawn of star formation in the universe. Its light took more than 13 billion years to reach Earth.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Swift Gamma-Ray Burst Mission consists of a robotic spacecraft called Swift, which was launched into orbit on November 20, 2004, at 17:16:00 UTC on a Delta II 7320-10C expendable launch vehicle. Swift is managed by the NASA Goddard Space Flight Center, and was developed by an international consortium from the United States, United Kingdom, and Italy. It is part of NASA’s Medium Explorer Program (MIDEX).

     
  • richardmitnick 8:15 am on October 31, 2015 Permalink | Reply
    Tags: , , Gamma Ray Bursts,   

    From NASA Blueshift: “Back to School with GRB 101” 

    NASA Blueshift
    NASA Blueshift

    October 30, 2015
    Barb Mattson

    Up until a few years ago, gamma-ray bursts (or GRBs, for short) were arguably the biggest mystery in high-energy astronomy. Basically, gamma-ray bursts are brief, extremely bright bursts of gamma-rays (as the name implies). They appeared at random across the sky. But what are they? What causes that burst? And what can we learn from them?

    I find it hard to talk about gamma-ray bursts without going into the history, because it’s such a recently solved mystery. The mystery is so recent that I had a professor in grad school who mused that watching gamma-ray burst scientists was a bit like watching 6-year-olds play soccer. Just as the 6-year-olds run in a clump following the ball from one side of the field to another, the scientists would follow each new piece of evidence, which took them in a new direction.

    I’ll keep the history to a minimum, but you can read more on the Swift education site. Gamma-ray bursts were first discovered by the Vela satellites in the late 1960s. The primary job of the Vela satellites was to monitor the sky for gamma rays from Earth, which would be evidence of a nation testing nuclear weapons. The satellites started seeing bursts of gamma-rays, but they were instantly recognizable as coming from beyond Earth. Since those events weren’t Vela’s primary mission, the data for those bursts results sat in someone’s desk drawer for years until he had time to look back at them.

    1
    The Vela 5 satellites in the cleanroom. These were the first satellites to detect gamma-ray bursts. Image courtesy of Los Alamos National Laboratory.

    The biggest challenge of studying GRBs is that the burst of gamma-rays lasts for only a few seconds up to a couple minutes before disappearing completely. Early on, it was difficult to tell exactly where in the sky they were. In part, because they happened so quickly, but also because we needed better gamma-ray detectors. Before there was a single gamma-ray detector that could localize a GRB, astronomers used a variety of detectors with poor localization, but widely separated. Doing that, they could triangulate positions. The more detectors, the better they could localize the GRB.

    The next challenge was figuring out where the GRBs originated. Were they part of our galaxy? Or did they come from much further away? These were very bright bursts for a very short amount of time — putting out more energy than our entire sun will emit in its lifetime, but in just a few seconds! And at first, scientists couldn’t image that these powerful explosions could be from outside our galaxy. Such a bright burst would have to be come from extraordinary explosions to be seen that far away.

    2
    GRBs appear randomly across the sky as this all-sky map of the locations of over 2700 bursts detected by the BATSE instrument aboard the Compton Gamma Ray Observatory shows. Credit: NASA

    In 1997 when a satellite called BeppoSAX detected the first X-ray “afterglow” from a gamma-ray burst.

    BeppoSAX satellite
    BeppoSAX

    Afterglow is emission that lingers after the initial burst of gamma-rays. For the first time, astronomers were able to study a burst site after the GRB faded AND, even better, they could take a spectrum of the X-ray emission to find the distance. It turns out GRBs are distant. Very distant. Gamma-ray bursts are one of the most distant things we can detect.

    Since then, gamma-ray burst observations have focused on seeing the afterglow as soon as possible. It can be seen in X-ray, optical, ultraviolet, and radio wavelengths. Based on these observations, it started to become clear that most GRBs are associated with supernova explosions. Not all supernovae explosions create GRBs, and understanding the conditions that create a GRB are part of current research.

    3
    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 black hole, collisions within the jet, and from the jet’s interaction with its surroundings. Credit: NASA

    Our division at Goddard has two of the premiere satellites that are currently used for the study of GRBs – Swift and Fermi – so Blueshift has talked about GRBs a few times in the past.

    NASA SWIFT Telescope
    NASA/Swift

    NASA Fermi Telescope
    NASA/Fermi

    Blueshift interviewed the Principal Investigator of the Swift mission on the occasion of its 10th anniversary
    Blueshift talks about the other type of gamma-ray burst in their Awesomeness Round-up from April 11, 2011
    Listen to the podcast “We’re Back” to learn more about how Fermi studies GRBs
    Listen to the podcast “Life and Death” to hear about how Swift helped solve the mystery of GRBs

    See the full article here .

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition

    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.

    NASANASA Goddard Banner

     
  • richardmitnick 2:55 pm on September 23, 2015 Permalink | Reply
    Tags: , , , Gamma Ray Bursts,   

    From AAS NOVA: ” Collapsing Enormous Stars” 

    AASNOVA

    Amercan Astronomical Society

    23 September 2015
    Susanna Kohler

    1
    A scene from a computer animation of a star collapsing to form a gamma-ray burst. A recent study suggests such events could happen on a much larger scale in the distant universe. [NASA / SkyWorks Digital]

    One of the big puzzles in astrophysics is how supermassive black holes (SMBHs) managed to grow to the large sizes we’ve observed in the very early universe. In a recent study, a team of researchers examines the possibility that they were formed by the direct collapse of supermassive stars.

    Formation Mystery

    SMBHs billions of times as massive as the Sun have been observed at a time when the universe was less than a billion years old. But that’s not enough time for a stellar-mass black hole to grow to SMBH-size by accreting material — so another theory is needed to explain the presence of these monsters so early in the universe’s history. A new study, led by Tatsuya Matsumoto (Kyoto University, Japan), poses the following question: what if supermassive stars in the early universe collapsed directly into black holes?

    Previous studies of star formation in the early universe have suggested that, in the hot environment of these primordial times, stars might have been able to build up mass much faster than they can today. This could result in early supermassive stars roughly 100,000 times more massive than the Sun. But if these early stars end their lives by collapsing to become massive black holes — in the same way that we believe massive stars can collapse to form stellar-mass black holes today — this should result in enormously violent explosions. Matusmoto and collaborators set out to model this process, to determine what we would expect to see when it happens!

    Energetic Bursts

    The authors modeled the supermassive stars prior to collapse and then calculated whether a jet, created as the black hole grows at the center of the collapsing star, would be able to punch out of the stellar envelope. They demonstrated that the process would work much like the widely-accepted collapsar model of massive-star death, in which a jet successfully punches out of a collapsing star, violently releasing energy in the form of a long gamma-ray burst (GRB).

    Because the length of a long GRB is thought to be proportional to the free-fall timescale of the collapsing star, the collapse of these supermassive stars would create much longer GRBs than are typical of massive stars today. Instead of the typical long-GRB length of ~30 seconds, these ultra-long GRBs would be 104–106 seconds.

    Interestingly, we have already detected a small number of ultralong GRBs; they make up the tail end of the long GRB duration distribution. Could these detections be signals of collapsing supermassive stars in the early universe? According to the authors’ estimates, we could optimistically expect to detect roughly one of these events per year — so it’s entirely possible!
    Citation

    Tatsuya Matsumoto et al 2015 ApJ 810 64. doi:10.1088/0004-637X/810/1/64

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 7:35 pm on September 11, 2015 Permalink | Reply
    Tags: , , Gamma Ray Bursts   

    From CfA: “Shocks in a Distant Gamma-Ray Burst” 

    Smithsonian Astrophysical Observatory
    Smithsonian Astrophysical Observatory

    September 11, 2015
    No Writer Credit

    Gamma ray bursts (GRBs)–flashes of high-energy light occur about once a day, randomly, from around the sky–are the brightest events in the known universe. While a burst is underway, it is many millions of times brighter than an entire galaxy. Astronomers are anxious to decipher their nature not only because of their dramatic energetics, but also because their tremendous brightness enables them to be seen across cosmological distances and times, providing windows into the young universe.

    1
    This all-sky map shows the locations of Swift’s 500 gamma-ray bursts, color coded by the year in which they occurred. In the background, an infrared image shows the location of our galaxy and its largest satellites. Credit: NASA/Swift/Francis Reddy

    NASA SWIFT Telescope
    NASA/Swift

    There appear to be two general types of GRBs: those associated with the deaths of massive stars, and ones believed to originate from the coalescence of two extreme objects (neutron stars or black holes) that had been orbiting each other in a binary system. In general the two types can be distinguished by the lengths of their bursts, the former lasting longer than a few seconds, while the latter are briefer. Astronomers think that, despite the differences, both kinds of GRBs have hot discs accreting material leading to the production of bipolar jets of charged particles moving at relativistic speeds. In the standard model, shocks internal to the fireball produce the gamma-rays in the first (longer duration) case, while shocks from the jets’ interactions with the external medium produce the initial burst of gamma-rays in the second case. Many details are similar in both scenarios, however, while some others vary according to the type, and astronomers have been trying to constrain these various parameters so that they can trace the origin of each GRB more precisely.

    CfA astronomer Raffaella Margutti and her colleagues used several ground-based telescopes to follow-up a GRB event that went off in June of 2014, examining the afterglow from about three days after the detection to about one hundred and twenty days later. They conclude that the burst is associated with a massive star’s death (a supernova), but find that some of its emission apparently results from shocks external to the fireball as are seen in the less luminous class of GRBs. The results are consistent with the predictions of supernova modeling, but the fact that this object spans both classes highlights the complexity of the sometimes-overlapping physical processes at work and the importance of observations at multiple wavelengths.
    Reference(s):

    “GRB 140606B/iPTF14bfu: Detection of Shock-Breakout Emission from a Cosmological γ-Ray Burst,” Zach Cano, A. de Ugarte Postigo, D. Perley, T. Kruhler, R. Margutti, M. Friis, D. Malesani, P. Jakobsson, J. P. U. Fynbo, J. Gorosabel, J. Hjorth, R. Sanchez-Ramırez, S. Schulze, N. R. Tanvir, C. C. Thone, and D. Xu, MNRAS 452, 1535, 2015.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    About CfA

    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. The long relationship between the two organizations, which began when the SAO moved its headquarters to Cambridge in 1955, was formalized by the establishment of a joint center in 1973. The CfA’s history of accomplishments in astronomy and astrophysics is reflected in a wide range of awards and prizes received by individual CfA scientists.

    Today, some 300 Smithsonian and Harvard scientists cooperate in broad programs of astrophysical research supported by Federal appropriations and University funds as well as contracts and grants from government agencies. These scientific investigations, touching on almost all major topics in astronomy, are organized into the following divisions, scientific departments and service groups.

     
  • richardmitnick 9:56 am on September 7, 2015 Permalink | Reply
    Tags: , , Gamma Ray Bursts,   

    From phys.org: “Surprising giant ring-like structure in the universe” 

    physdotorg
    phys.org

    September 7, 2015
    Tomasz Nowakowski

    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.

    Five billion light years is a distance almost inconceivable, even on a cosmic scale. To better illustrate the extent of this physical quantity, it’s enough to say that 35,000 galaxies the size of our Milky Way are needed to cover that distance. Thanks to a surprising discovery made by a Hungarian-U.S. team of astronomers, now we know that a structure this big really exists in the observable universe.

    The researchers found a ring of nine gamma ray bursts (GRBs)—the most luminous events in the universe—about 5 billion light years in diameter, and having a nearly regular circular shape, noting that there is a one in 20,000 probability of the GRBs being in this distribution by chance. They published their findings on July 27 in the Monthly Notices of the Royal Astronomical Society.

    Lajos Balazs of Konkoly Observatory in Budapest, Hungary who led the team of astronomers, cannot hide how surprise he was when a feature so large was discovered.

    “Until now GRBs are the only objects for which we know the spatial distribution in the whole observable universe. All other objects are complete only in a restricted part of the sky. Our discovery has revealed a large-scale regular feature not known before. Large scale objects like GRB groups have been known already, but such a regular circular structure was a surprise,” Balazs told Phys.org.

    The newly-found ring-shaped feature is large enough to contradict the cosmological principle (CP), which sets a theoretical limit of 1.2 billion light years for the largest structures. The researchers assume that the ring could be a projection of a spheroidal structure and we see it nearly face-on because of the small variations of GRB distances around the object’s center.

    Although they claim to have found evidence for a regular structure, the apparent shape of this ring is based only on a visual impression.

    The astronomers conclude that the ring is probably not a real physical structure. But further studies are needed to reveal whether or not the structure could have been produced by a low-frequency spatial harmonic of the large-scale matter density distribution or of universal star-forming activity.

    “It would be important to increase the number of GRBs with known redshift, consequently with known distances, and to study the distribution of galaxies potentially hosting GRBs in more detail,” Balazs said.

    GRBs are the brightest electromagnetic events known to occur in the universe. They release as much energy in a few seconds as the Sun does over its 10-billion-year lifetime. GRBs are believed to be the result of massive stars collapsing into black holes. But the problem of forming GRBs is still not completely settled.

    “According to the widely accepted view, the GRBs have two basic types. The short duration ones, less than a couple of seconds, are formed by two coalescing neutron stars, while the longer ones resulted in collapsing stars of 20 to 40 solar masses,” Balazs revealed.

    The majority of the observed GRBs are resulted in collapsing high-mass stars. GRBs are very rare transient phenomena. Consequently, the observed spatial distribution is a serious under-sampling of the space distribution of galaxies in general. Furthermore, the high-mass stars have short lifetimes; thus, GRBs prefer those galaxy hosts having considerable star-forming activity.

    The known number of GRBs now exceeds a couple of thousand and is steadily increasing with ongoing observations.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 8:14 pm on August 4, 2015 Permalink | Reply
    Tags: , , Gamma Ray Bursts,   

    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.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

     
  • richardmitnick 12:27 pm on July 8, 2015 Permalink | Reply
    Tags: , , , , Gamma Ray Bursts,   

    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.

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition
    Visit ESO in Social Media-

    Facebook

    Twitter

    YouTube

    ESO Bloc Icon

    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”.

    ESO LaSilla
    LaSilla

    ESO VLT Interferometer
    VLT

    ESO Vista Telescope
    VISTA

    ESO VLT Survey telescope
    VLT Survey Telescope

    ALMA Array
    ALMA

    ESO E-ELT
    E-ELT

    ESO APEX
    Atacama Pathfinder Experiment (APEX) Telescope

     
  • richardmitnick 10:13 am on May 27, 2015 Permalink | Reply
    Tags: , , Gamma Ray Bursts, , ,   

    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.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    LLNL Campus

    Operated by Lawrence Livermore National Security, LLC, for the Department of Energy’s National Nuclear Security
    Administration
    DOE Seal
    NNSA

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: