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  • richardmitnick 4:52 pm on August 11, 2014 Permalink | Reply
    Tags: , , , , Dark Sky Simulations, SLAC Kavli,   

    From Symmetry: “Open access to the universe” 

    Symmetry

    August 08, 2014
    Lori Ann White

    A team of scientists generated a giant cosmic simulation—and now they’re giving it away.

    A small team of astrophysicists and computer scientists have created some of the highest-resolution snapshots yet of a cyber version of our own cosmos. Called the Dark Sky Simulations, they’re among a handful of recent simulations that use more than 1 trillion virtual particles as stand-ins for all the dark matter that scientists think our universe contains.

    dss
    Courtesy of Dark Sky Simulations collaboration

    They’re also the first trillion-particle simulations to be made publicly available, not only to other astrophysicists and cosmologists to use for their own research, but to everyone. The Dark Sky Simulations can now be accessed through a visualization program in coLaboratory, a newly announced tool created by Google and Project Jupyter that allows multiple people to analyze data at the same time.

    To make such a giant simulation, the collaboration needed time on a supercomputer. Despite fierce competition, the group won 80 million computing hours on Oak Ridge National Laboratory’s Titan through the Department of Energy’s 2014 INCITE program.

    titan

    In mid-April, the group turned Titan loose. For more than 33 hours, they used two-thirds of one of the world’s largest and fastest supercomputers to direct a trillion virtual particles to follow the laws of gravity as translated to computer code, set in a universe that expanded the way cosmologists believe ours has for the past 13.7 billion years.

    “This simulation ran continuously for almost two days, and then it was done,” says Michael Warren, a scientist in the Theoretical Astrophysics Group at Los Alamos National Laboratory. Warren has been working on the code underlying the simulations for two decades. “I haven’t worked that hard since I was a grad student.”

    Back in his grad school days, Warren says, simulations with millions of particles were considered cutting-edge. But as computing power has increased, particle counts did too. “They were doubling every 18 months. We essentially kept pace with Moore’s Law.”

    When planning such a simulation, scientists make two primary choices: the volume of space to simulate and the number of particles to use. The more particles added to a given volume, the smaller the objects that can be simulated—but the more processing power needed to do it.

    Current galaxy surveys such as the Dark Energy Survey are mapping out large volumes of space but also discovering small objects. The under-construction Large Synoptic Survey Telescope “will map half the sky and can detect a galaxy like our own up to 7 billion years in the past,” says Risa Wechsler, Skillman’s colleague at KIPAC who also worked on the simulation. “We wanted to create a simulation that a survey like LSST would be able to compare their observations against.”

    LSST Telescope
    LSST

    The time the group was awarded on Titan made it possible for them to run something of a Goldilocks simulation, says Sam Skillman, a postdoctoral researcher with the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford and SLAC National Accelerator Laboratory. “We could model a very large volume of the universe, but still have enough resolution to follow the growth of clusters of galaxies.”

    The end result of the mid-April run was 500 trillion bytes of simulation data. Then it was time for the team to fulfill the second half of their proposal: They had to give it away.

    They started with 55 trillion bytes: Skillman, Warren and Matt Turk of the National Center for Supercomputing Applications spent the next 10 weeks building a way for researchers to identify just the interesting bits—no pun intended— and use them for further study, all through the Web.

    “The main goal was to create a cutting-edge data set that’s easily accessed by observers and theorists,” says Daniel Holz from the University of Chicago. He and Paul Sutter of the Paris Institute of Astrophysics, helped to ensure the simulation was based on the latest astrophysical data. “We wanted to make sure anyone can access this data—data from one of the largest and most sophisticated cosmological simulations ever run—via their laptop.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.


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  • richardmitnick 7:51 pm on April 8, 2014 Permalink | Reply
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    From SLAC: “Stalking Gamma Rays from the Ground” 

    KIPAC scientists are helping build a cutting-edge camera for the Cherenkov Telescope Array, an advanced, ground-based gamma-ray observatory

    Cherenkov Telescope Array
    Cherenkov Telescope Array

    April 8, 2014
    Lori Ann White

    Key components for a new type of camera that will collect only the faintest, fastest flashes of light in the night sky are being assembled and tested now at SLAC. Their eventual destination: the first Compact High-energy Camera (CHEC), which will be installed in a prototype telescope for the Cherenkov Telescope Array.

    chec
    The CHEC camera mechanical structure and a TARGET Module.

    The CTA is a ground-based gamma-ray observatory currently under development by an international consortium with more than 1000 members from 27 countries. The CTA will detect ultra-high-energy gamma rays, which are beyond even the reach of the Fermi Gamma-ray Space Telescope. Current plans call for the observatory to comprise two separate arrays – one in the Northern Hemisphere and one in the Southern Hemisphere – totaling more than 100 telescopes of three different sizes.

    The telescopes are now under development. Researchers at SLAC are testing modules of electronic components for the first CHEC camera, which will be installed on a prototype telescope later this year.

    But most gamma rays from cosmic sources are blocked by the Earth’s atmosphere. What will the camera be looking at?

    ‘Seeing’ Gamma Rays

    Gamma rays are the most energetic form of electromagnetic radiation – energetic enough they cause showers of secondary particles when they hit the atmosphere. The particles race toward the ground so fast they break the speed of light in our atmosphere. This is considerably slower than the speed of light in a vacuum, but still speedy enough to cause them to emit a form of radiation called Cherenkov radiation.

    “It’s really just light – bluish light,” said Stefan Funk, an astrophysicist at the Kavli Institute for Particle Astrophysics and Cosmology, a joint SLAC-Stanford institute. Faint blue light that flashes on and off in about five nanoseconds: “If we had nanosecond eyes, we could see it,” he said.

    Unfortunately we don’t have nanosecond eyes, and neither do CCD cameras, which are the type of camera generally used at observatories to collect light. That’s where the CHEC camera comes in.

    Nanosecond Eyes

    Each CHEC camera contains modules of customized electronic components, beginning with photomultipliers. A photomultiplier can capture a single photon, or particle of light, and amplify its signal for a detector to read. But the real heart of each module is a special integrated circuit chip called a TARGET chip, developed at the University of Hawaii in collaboration with SLAC researchers. Each TARGET chip can read the signals from 16 individual pixels on a photomultiplier one billion times a second – fast enough to capture the flashes of Cherenkov light.

    photomult
    This colorful piece of electronics is a photomultiplier module for the CHEC camera undergoing testing. (Fabricio Sousa/SLAC)

    “The prototype camera we’re building uses 32 modules, each with a 64-pixel photomultiplier and four TARGET chips,” said KIPAC postdoctoral researcher Luigi Tibaldo. “It will be installed on a prototype of the smallest telescope,” which represents the majority of instruments needed for the arrays; the TARGET chips are also under consideration for some of the mid-sized telescopes under development. This adds up to around 60 telescopes to equip, making cost an important factor in the design.

    all
    All 32 of the photomultiplier modules for the CHEC camera. (Tobias Jogler/SLAC)

    To address this issue, the modules can easily be mass-produced, Funk said. Their colleague Gary Varner of the University of Hawaii works with industry partners to create the TARGET chips and the photomultipliers are supplied by Hamamatsu Photonics, a Japanese firm.

    Later this month, after Tibaldo and his colleagues at SLAC have finished assembling and testing the modules, they’ll be shipped to collaboration partners at the University of Leicester in England for more tests and final assembly into a camera, a step Funk says he’s eagerly awaiting.

    three
    Luigi Tibaldo of SLAC (center) and collaborators Shigeki Hirose if the University of Nagoya (left) and Mark Bryan of the University of Amsterdam (right) in Building 84, where they’re testing the photomultiplier modules for the CHEC camera. (Fabricio Sousa/SLAC)

    “The good thing about having our modules assembled into a camera now is that we’ll learn a lot that will help us make the entire package – telescopes and cameras – better,” he said.

    See the full article here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 1:18 pm on April 3, 2014 Permalink | Reply
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    From Symmetry: “Possible hints of dark matter in Fermi data” 

    April 03, 2014
    No Writer Credit

    A new study of gamma-ray light from the center of our galaxy makes the strongest case to date that some of this emission may arise from dark matter, an unknown substance making up most of the material universe.

    Using publicly available data from NASA’s Fermi Gamma-ray Space Telescope, independent scientists at the Fermi National Accelerator Laboratory, the Harvard-Smithsonian Center for Astrophysics, the Massachusetts Institute of Technology and the University of Chicago have developed new maps showing that the galactic center produces more high-energy gamma rays than can be explained by known sources and that this excess emission is consistent with some forms of dark matter.

    NASA Fermi Telescope
    Fermi

    “The new maps allow us to analyze the excess and test whether more conventional explanations, such as the presence of undiscovered pulsars or cosmic-ray collisions on gas clouds, can account for it,” says Dan Hooper, an astrophysicist at Fermilab and a lead author of the study. “The signal we find cannot be explained by currently proposed alternatives and is in close agreement with the predictions of very simple dark matter models.”

    gc

    The galactic center (shown above) teems with gamma-ray sources, from interacting binary systems and isolated pulsars to supernova remnants and particles colliding with interstellar gas. It’s also where astronomers expect to find the galaxy’s highest density of dark matter, which only affects normal matter and radiation through its gravity. Large amounts of dark matter attract normal matter, forming a foundation upon which visible structures, like galaxies, are built.

    No one knows the true nature of dark matter, but WIMPs, or Weakly Interacting Massive Particles, represent a leading class of candidates. Theorists have envisioned a wide range of WIMP types, some of which may either mutually annihilate or produce an intermediate, quickly decaying particle when they collide. Both of these pathways end with the production of gamma rays—the most energetic form of light—at energies within the detection range of Fermi’s Large Area Telescope, or LAT.

    NASA Fermi Large Area Telescope
    LAT

    When astronomers carefully subtract all known gamma-ray sources from LAT observations of the galactic center, a patch of leftover emission remains (shown above, on right). This excess appears most prominent at energies between 1 and 3 billion electron volts—roughly a billion times greater than that of visible light—and extends outward at least 5000 light-years from the galactic center.

    Hooper and his colleagues conclude that annihilations of dark matter particles with a mass between 31 and 40 GeV provide a remarkable fit for the excess based on its gamma-ray spectrum, its symmetry around the galactic center, and its overall brightness. Writing in a paper submitted to the journal Physical Review D, the researchers say that these features are difficult to reconcile with other explanations proposed so far, although they note that plausible alternatives not requiring dark matter may yet materialize.

    “Dark matter in this mass range can be probed by direct detection and by the Large Hadron Collider, so if this is dark matter, we’re already learning about its interactions from the lack of detection so far,” says co-author Tracy Slatyer, a theoretical physicist at MIT in Cambridge, Massachusetts. “This is a very exciting signal, and while the case is not yet closed, in the future we might well look back and say this was where we saw dark matter annihilation for the first time.”

    The researchers caution that it will take multiple sightings—in other astronomical objects, the LHC or in some of the direct-detection experiments now being conducted around the world—to validate their dark matter interpretation.

    “Our case is very much a process-of-elimination argument. We made a list, scratched off things that didn’t work, and ended up with dark matter,” says co-author Douglas Finkbeiner, a professor of astronomy and physics at the CfA, also in Cambridge.

    “This study is an example of innovative techniques applied to Fermi data by the science community,” says Peter Michelson, a professor of physics at Stanford University in California and the LAT principal investigator. “The Fermi LAT Collaboration continues to examine the extraordinarily complex central region of the galaxy, but until this study is complete we can neither confirm nor refute this interesting analysis.”

    While the great amount of dark matter expected at the galactic center should produce a strong signal, competition from many other gamma-ray sources complicates any case for a detection. But turning the problem on its head provides another way to attack it. Instead of looking at the largest nearby collection of dark matter, look where the signal has fewer challenges.

    Dwarf galaxies orbiting the Milky Way lack other types of gamma-ray emitters and contain large amounts of dark matter for their size – in fact, they’re the most dark-matter-dominated sources known. But there’s a tradeoff. Because they lie much farther away and contain much less total dark matter than the center of the Milky Way, dwarf galaxies produce a much weaker signal and require many years of observations to establish a secure detection.

    For the past four years, the LAT team has been searching dwarf galaxies for hints of dark matter. The published results of these studies have set stringent limits on the mass ranges and interaction rates for many proposed WIMPs, even eliminating some models. In the study’s most recent results, published in Physical Review D on February 11, the Fermi team took note of a small but provocative gamma-ray excess.

    “There’s about a one-in-12 chance that what we’re seeing in the dwarf galaxies is not even a signal at all, just a fluctuation in the gamma-ray background,” explained Elliott Bloom, a member of the LAT Collaboration at the Kavli Institute for Particle Astrophysics and Cosmology, jointly located at the SLAC National Accelerator Laboratory and Stanford University. If it’s real, the signal should grow stronger as Fermi acquires additional years of observations and as wide-field astronomical surveys discover new dwarfs. “If we ultimately see a significant signal,” he added, “it could be a very strong confirmation of the dark matter signal claimed in the galactic center.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.



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  • richardmitnick 12:44 pm on November 28, 2013 Permalink | Reply
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    From SLAC: “The Seven Biggest Questions in Particle Astrophysics and Cosmology” 

    November 27, 2013
    Andy Freeberg

    The cosmic frontier. This is the name physicists give the ambitious questions they are trying to answer through observations of outer space. These questions aren’t only in the interest of astronomy; in fact, they’re promising paths to understanding the fundamental physics of our world.

    To celebrate the 10th anniversary of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), SLAC recently hosted many of the top scientists in the field to discuss the most important mysteries to confront in the coming decade.

    Where Did That Come From? Cosmic Rays and Intergalactic Particle Accelerators

    After a century of study, researchers still struggle to understand the origin of cosmic rays, particles with unearthly, extreme energies that fill the universe and bombard our planet from all directions. Scientists believe these high-energy oddities play a key role influencing the physics and chemistry that form stars and planets, and even influence life on Earth by occasionally causing mutations in DNA.

    And yet, the exact ways in which cosmic rays are accelerated remains a major open question. We’ve discovered where many come from within our galaxy, but the most extreme cosmic rays continue to confound us.

    KIPAC’s Luigi Tibaldo interviews Angela Olinto of the University of Chicago and Neil Gehrels of NASA’s Goddard Space Flight Center about particle acceleration in the universe. (Luigi Tibaldo & Andy Freeberg/SLAC)

    What is the Dark Matter?

    Given our standard theory of gravity, observations tell us there must be a lot more mass holding things like our Milky Way galaxy together than we can see. Scientists’ suspicion is that this missing mass is composed of a new kind of “dark matter,” a material with one or more particles that should be detectable by experiments.

    This is a particularly exciting time for dark matter study because there are some intriguing clues pointing to where dark matter particles might be hiding. These clues are helping researchers develop a variety of searches. The three major strategies are direct detection, collider production and indirect detection.

    KIPAC’s Andrea Albert interviews Southern Methodist’s Jodi Cooley-Sekula and Stanford’s Alex Drlica-Wagner and asks them to explain what we currently know about dark matter and what we hope to find out in the coming years. (Andrea Albert & Andy Freeberg/SLAC)

    What Can Compact Objects Teach Us? Black Holes and Neutron Stars, Extreme Physics in Small Packages

    Enormously powerful gravitational fields that warp the local fabric of space and time. Incomparably strong magnetic fields that can stretch atoms themselves into long spindles. Materials so dense a teaspoonful would weigh billions of tons. These are just some of the exotic properties of compact objects, a catch-all term for several types of unbelievably dense and remarkable objects—white dwarfs, neutron stars and black holes.

    Compact objects are known to possess some of the most extreme physical properties ever observed. Scattered throughout our galaxy and beyond, these objects serve as astrophysical laboratories that test the very limits of physics as we know it.

    How Did This All Happen? Galaxy Formation and Evolution

    Over millions and millions of years galaxies form, grow and change. Gas accumulates, stars are born in some regions and voids fill others. To understand these processes, astrophysicists study snapshots from telescopes and try to piece them together with complex computer simulations.

    New observations are shedding fresh light on galaxies – from the earliest to form, to how galaxies start and stop creating stars, to the physics of galaxy clusters, the most massive objects in the universe. And while a general picture of galaxy formation and evolution is in place, there are still huge gaps in understanding how and why it all happens.

    KIPAC’s Rachel Reddick interviews UC Berkeley’s Eliot Quataert about the biggest challenges and opportunities in understanding the lives of galaxies. (Rachel Reddick & Andy Freeberg/SLAC)

    How Will We Make Sense of It All? Astronomically Big Data

    Astrophysics and cosmology deal with big everything: big datasets, big simulations and big collaborations. Researchers already have information on billions of astronomical objects, and expect to make measurements of many billions more in the next decade.

    Yet the challenge with such a large dataset is not so much in handling its size, but in its complexity. The struggle in trying to find a single rare star in a haystack of billions of near-identical stars, or understanding the relationships between every single galaxy in the universe, goes beyond simply the enormous number of gigabytes. As more and more data piles up, the teams who are most clever about analyzing and combining those datasets will be the ones who will likely make the biggest discoveries.

    KIPAC’s Debbie Bard interviews NYU’s David Hogg about the unique challenges of astrophysical data. (Debbie Bard & Andy Freeberg/SLAC)

    What Makes Up the Rest of the Universe? Dark Energy

    In the past 15 years or so, scientists have realized that the “stuff” making up all the atoms in all the galaxies, stars, planets, and humans we have ever observed only constitutes about 5 percent of the universe. While we might be close to pinning down the nature of part (roughly 27 percent) of the missing stuff (see dark matter, above), what we know about the dominant (roughly 68 percent) component of the universe, what is being called “dark energy,” is still almost nothing.

    KIPAC’s Josh Meyers interviews Fermilab’s Josh Frieman, head of the Dark Energy Survey and also a professor at the University of Chicago, about what he hopes the coming years hold for dark energy research. (Josh Meyers & Andy Freeberg/SLAC)

    What Happened at the Beginning of the Universe? Inflation and Precision Cosmology

    Inflation refers to a time right after the Big Bang when the universe expanded extremely quickly. To compare, it’s like going from the size of a single atom to that of the entire Milky Way in less than 10-33 seconds! If scientists are correct, tiny fluctuations during this brief period were the seeds of the stars and galaxies and all other matter that we see today.

    The theories of inflation look great on paper, but scientists still need to test them with observations. Of course, it’s very challenging to “observe” something that happened over 13.8 billion years ago. Nonetheless, there’s been incredible progress recently in finding the traces that inflation left behind and upcoming experiments promise to provide even more evidence of what happened during the universe’s infancy.

    KIPAC’s Kimmy Wu interviews Stanford’s Eva Silverstein about how cosmologists are making progress in understanding the inflationary period. (Kimmy Wu & Andy Freeberg/SLAC)

    See the full article, complete with videos and papers by th participants, here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 8:33 am on October 31, 2013 Permalink | Reply
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    From SLAC: “Cosmos Seeded with Heavy Elements During Violent Youth” 

    October 30, 2013
    Lori Ann White

    New evidence of heavy elements spread evenly between the galaxies of the giant Perseus cluster supports the theory that the universe underwent a turbulent and violent youth more than 10 billion years ago. That explosive period was responsible for seeding the cosmos with the heavy elements central to life itself.

    pc

    Researchers from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), jointly run by Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory, shed light on this important era by analyzing 84 separate sets of X-ray telescope observations from the Japanese-US Suzaku satellite. Their results appear today in the journal Nature.

    “We saw that iron is spread out between the galaxies remarkably smoothly,” said Norbert Werner, lead author of the paper. “That means it had to be present in the intergalactic gas before the Perseus cluster formed.”

    The even distribution of these elements supports the idea that they were created at least 10 to 12 billion years ago. According to the paper, during this time of intense star formation, billions of exploding stars created vast quantities of heavy elements in the alchemical furnaces of their own destruction. This was also the epoch when black holes in the hearts of galaxies were at their most energetic. Young stars, exploding supernovae, and voraciously feeding black holes produced powerful winds 10-12 billion years ago. These winds were the spoon that lifted the iron from the galaxies and mixed it with the intergalactic gas. (Akihiro Ikeshita)

    “The combined energy of these cosmic phenomena must have been strong enough to expel most of the metals from the galaxies at early times, and to enrich and mix the intergalactic gas,” said co-author and KIPAC graduate student Ondrej Urban.

    To settle the question of whether the heavy elements created by supernovae remain mostly in their home galaxies or are spread out through intergalactic space, the researchers looked through the Perseus cluster in eight different directions. They focused on the hot, 10-million-degree gas that fills the spaces between galaxies and found the spectroscopic signature of iron reaching all the way to the cluster’s edges.

    “We estimate there’s about 50 billion solar masses of iron in the cluster,” said former KIPAC member and co-author Aurora Simionescu, who is currently with the Japanese Aerospace Exploration Agency as an International Top Young Fellow. “We think most of the iron came from a single type of supernova, called a Type Ia supernova.”

    In Type Ia supernovae the stars are destroyed and release all their material into the surrounding space. The researchers believe that at least 40 billion Type Ia supernovae must have exploded within a relatively short period on cosmological time scales in order to release that much iron and have the force to drive it out of the galaxies.

    The results suggest that the Perseus cluster is probably not unique, and that iron – along with other heavy elements – is evenly spread throughout all massive galaxy clusters, said Steven Allen, a KIPAC professor and head of the research team.

    “You are older than you think – or at least, some of the iron in your blood is older, formed in galaxies millions of light years away and billions of years ago,” Simionescu said.

    See the full article here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 12:39 pm on April 18, 2013 Permalink | Reply
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    From SLAC: “Novel Analysis Method Levels the Quasar Playing Field” 

    April 18, 2013
    Lori Ann White

    “In the nearly six decades since quasars were discovered, the list of these energetic galaxies powered by supermassive black holes has grown to more than 100,000 – enough examples to reveal important information about the quasar population as a whole. But attempts to conduct a celestial census of these powerful objects have been limited by a fundamental problem: Although quasars are bright, they also span billions of light years in distance from Earth. Just as with stars in an urban sky, the closest quasars can be seen even if they are dim, while the oldest and most distant ones can be seen only if they are bright. This means astrophysicists have to study a sample with big differences among individual members, including distance, age, brightness and type of radiation emitted.

    qua
    The interaction of a supermassive black hole and a disk of accreting matter, called a quasar, can be seen at the center of a faraway galaxy in this artist’s concept. It consists of a dusty, doughnut-shaped cloud of gas and dust that feeds a central supermassive black hole. As the black hole feeds, the gas and dust heat up and spray out different kinds of light, as illustrated by the white rays.

    Astrophysicists with the Kavli Institute for Particle Astrophysics and Cosmology, a joint SLAC-Stanford institute, found a way to reach past these limitations: They improved an algorithm that homes in on important commonalities of a population of objects while taking into account the limitations and biases for observations made in multiple types of electromagnetic radiation, such as optical light or radio waves – two of the most important wavelengths for studying quasars.

    In the process they shed new light on a contentious question: Are there two types of quasars, with one “louder” in radio than the other, or is there just one type with emissions that vary widely across the electromagnetic spectrum?”

    See the answers in the full article here.

    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

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  • richardmitnick 4:36 pm on November 28, 2012 Permalink | Reply
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    From Symmetry: “Stellar black widows entrap companion stars” 

    Of the hundreds of objects in the universe emitting gamma rays, two look to be “black widows,” ancient stars extending their lives by sucking in material from companion stars. Stanford physicist Roger Romani is hot on the trail of these extreme stars.

    November 27, 2012
    Lori Ann White

    rr
    Roger Romani

    “In its four years in orbit, the Fermi Gamma-ray Space Telescope has found a cosmos teeming with points of gamma-ray light. Newly discovered gamma-ray sources run the gamut from the expected, like supernova remnants and active galactic nuclei, to the surprising, like gamma rays from the sun or Earth-bound lightning strikes.


    Fermi

    But a considerable percentage of the gamma-ray sources discovered by Fermi can’t be matched up with any type of object, expected or not. Of the more than 1800 sources found by Fermi’s main instrument, the Large Area Telescope, in its first two years of operation, almost a third fell into this category.

    These “unassociated objects,” as they’re called, are the ones Stanford physics professor Roger Romani likes to study. Romani, a member of the Kavli Institute for Particle Astrophysics and Cosmology, an institute run jointly by Stanford and SLAC National Accelerator Laboratory, has spent the past few years identifying these sources. He’s found most of them to be common astronomical objects that, for one reason or another, were just a bit more difficult to recognize. Two of them, however, appear to be “black widows,” ancient stars extending their lives by sucking in material from companion stars. And there may be more….”

    Read on. It gets very interesting.

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.

     
  • richardmitnick 1:44 pm on August 21, 2012 Permalink | Reply
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    From SLAC Today: “Supernova Remnant a Giant Particle Collider in Space” 

    August 21, 2012
    Lori Ann White

    Scientists from SLAC publishing research about colliding particles should come as no surprise; the lab has been accelerating particles for 50 years. But these SLAC researchers are astrophysicists, and their research was published in the Astrophysical Journal. The researchers, from the joint SLAC-Stanford Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), along with colleagues from France and Japan, looked at a supernova remnant located about 3,000 light years away and discovered what is best described as a particle collider in space.

    image
    The left panel shows the gamma-ray emission from SNR147 as seen by the Fermi-LAT, while the right panel shows emission for a Hydrogen line transmission in optical light. The numbered regions are to aid in comparison. Image source

    Supernova remnants, giant clouds of dust and gas thrown off by a self-destructing star, are known to accelerate particles. They’re one source of the cosmic rays – in reality not rays, but super-accelerated charged particles like protons – that bombard Earth. But when the team analyzed several different observations of the supernova remnant SNR S147, including gamma-ray observations from the LAT instrument on the Fermi Gamma-ray Space Telescope, they discovered something more than accelerating particles.

    Wanna know what they saw? See the full article here.

    Also check out “Gamma-ray Emitting Supernova Remnant Is a Giant Particle Collider In Space“, an article by Jack Singal in the KIPAC Collaboration Space.

    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 11:43 am on April 30, 2012 Permalink | Reply
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    From SLAC Today: “KIPAC Study Sheds Light on Cosmic Jets” 

    April 30, 2012
    David Reffkin

    “The cosmos contains particle accelerators that are much more powerful than our biggest machines. They are powered by black holes and their surrounding disks of matter, called accretion disks. As matter swirls into the black hole, the interaction emits enormous jets of particles and radiation traveling at nearly the speed of light.

    The commonly accepted theory for the development of the jets is called the Blandford-Znajek Mechanism, named for Roger Blandford and Roman Znajek. Blandford, a physics professor at Stanford, also directs the Kavli Institute for Astroparticle Physics and Cosmology (KIPAC), which is jointly run by SLAC and the university.

    In 1977, the scientists suggested that part of the energy needed to accelerate the particles is extracted from the rotational energy of the hole. However, there are still many details to learn about the process that launches such enormous jets of energy.

    Because these cosmic accelerators are far away, and because the accretion disk of matter surrounds the black hole, the launching of the jets can’t be seen directly. Enter simulations, which allow scientists to probe the extreme physics within these systems by entering the initial conditions into a computer and allowing systems to evolve according to the relevant physics.”

    image
    Visualization of a simulated vertical slice through an accreting disk of matter around a black hole. Mass of varying density (blue is low, red is high) is pushing through the magnetic field (black lines) into the hole. Image courtesy KIPAC

    See the full article here.

    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
    i1

     
  • richardmitnick 3:13 pm on April 18, 2012 Permalink | Reply
    Tags: , , , , SLAC Kavli,   

    From SLAC Today: “Fermi Uses Gamma Rays to Unearth Clues About “Empty” Space” 

    April 18, 2012
    David Reffkin

    “The SLAC-built Large Area Telescope (LAT), the main instrument of the Fermi Gamma-ray Space Telescope, has been studying the gamma-ray sky for almost four years. During that time, the LAT has identified hundreds of gamma-ray sources, including pulsars and active galactic nuclei. It has shown that the Crab Nebula isn’t the steady emitter of gamma rays it’s long been thought to be. The LAT has catalogued lightning in the Earth’s atmosphere and flares on the sun.

    But, as reported in a paper soon to appear in The Astrophysical Journal, most of the gamma rays detected by the LAT cannot be attributed to individual point sources.

    The study was led by Gudlaugar Johannesson, a former postdoctoral researcher member and current affiliate of the SLAC- and Stanford-based Kavli Institute for Particle Astrophysics and Cosmology who is now at the University of Iceland; Andrew Strong of the Max Planck Institute in Garching, Germany; and KIPAC and Stanford scientist Troy Porter.”


    L.A.T.


    Fermi Gamma Ray Telescope

    See the full article here.

    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science. i1

     
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