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  • richardmitnick 5:51 pm on April 4, 2017 Permalink | Reply
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    From Swinburne: “Mysterious bursts of energy do come from outer space” 

    Swinburne U bloc

    Swinburne University

    1
    Artist’s impression shows three bright red flashes depicting fast radio bursts far beyond the Milky Way, appearing in the constellations Puppis and Hydra. Credit: James Josephides/Mike Dalley.

    3 April 2017
    Lea Kivivali
    +61 3 9214 5428
    lkivivali@swin.edu.au

    Fast Radio Bursts present one of modern astronomy’s greatest mysteries: what or who in the Universe is transmitting short bursts of radio energy across the cosmos?

    Manisha Caleb, a PhD candidate at Australian National University, Swinburne University of Technology and the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), has confirmed that the mystery bursts of radio waves that astronomers have hunted for ten years really do come from outer space.

    Ms Caleb worked with Swinburne and University of Sydney colleagues to detect three of these Fast Radio Bursts (FRBs) with the Molonglo radio telescope 40 km from Canberra.

    U Sidney Molonglo Observatory Synthesis Telescope (MOST), Hoskinstown, Australia

    Discovered almost 10 years ago at CSIRO’s Parkes radio telescope, Fast Radio Bursts are millisecond-duration intense pulses of radio light that appear to be coming from vast distances.

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

    They are about a billion times more luminous than anything we have ever seen in our own Milky Way galaxy.

    One potential explanation of the mystery is that they weren’t really coming from outer space, but were some form of local interference tricking astronomers into searching for new theories of their ‘impossible’ radio energy.

    “Perhaps the most bizarre explanation for the FRBs is that they were alien transmissions,” says ARC Laureate Fellow Professor Matthew Bailes from Swinburne.

    “Conventional single dish radio telescopes have difficulty establishing that transmissions originate beyond the Earth’s atmosphere,” says Swinburne’s Dr Chris Flynn.

    Molonglo opens new window on the Universe

    In 2013 CAASTRO scientists and engineers realised that the Molonglo telescope’s unique architecture could place a minimum distance to the FRBs due to its enormous focal length. A massive re-engineering effort began, which is now opening a new window on the Universe.

    The Molonglo telescope has a huge collecting area (18,000 square metres) and a large field of view (eight square degrees on the sky), which makes it excellent for hunting for fast radio bursts.

    Ms Caleb’s project was to develop software to sift through the 1000 TB of data produced each day. Her work paid off with the three new FRB discoveries.

    “It is very exciting to see the University of Sydney’s Molonglo telescope making such important scientific discoveries by partnering with Swinburne’s expertise in supercomputing”, says Professor Anne Green of the University of Sydney.

    Thanks to further funding from the Australian Research Council the telescope will be improved even more to gain the ability to localise bursts to an individual galaxy.

    “Figuring out where the bursts come from is the key to understanding what makes them. Only one burst has been linked to a specific galaxy,” Ms Caleb says. “We expect Molonglo will do this for many more bursts.”

    A paper on the discovery ‘The first interferometric detections of Fast Radio Bursts’ has been accepted for publication in Monthly Notices of the Royal Astronomical Society. It is available online at https://arxiv.org/abs/1703.10173

    See the full article here .

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    Swinburne U Campus

    Swinburne is a large and culturally diverse organisation. A desire to innovate and bring about positive change motivates our students and staff. The result is in an institution that grows and evolves each year.

     
  • richardmitnick 1:41 pm on February 14, 2017 Permalink | Reply
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    From CfA: “Astronomers Propose a Cell Phone Search for Galactic Fast Radio Bursts” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    February 14, 2017
    Christine Pulliam
    Media Relations Manager
    Harvard-Smithsonian Center for Astrophysics
    617-495-7463
    cpulliam@cfa.harvard.edu

    1

    Fast radio bursts (FRBs) are brief spurts of radio emission, lasting just one-thousandth of a second, whose origins are mysterious. Fewer than two dozen have been identified in the past decade using giant radio telescopes such as the 1,000-foot dish in Arecibo, Puerto Rico.

    NAIC/Arecibo Observatory, Puerto Rico, USA
    NAIC/Arecibo Observatory, Puerto Rico, USA

    Of those, only one has been pinpointed to originate from a galaxy about 3 billion light-years away.

    The other known FRBs seem to also come from distant galaxies, but there is no obvious reason that, every once in a while, an FRB wouldn’t occur in our own Milky Way galaxy too. If it did, astronomers suggest that it would be “loud” enough that a global network of cell phones or small radio receivers could “hear” it.

    “The search for nearby fast radio bursts offers an opportunity for citizen scientists to help astronomers find and study one of the newest species in the galactic zoo,” says theorist Avi Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA).

    Previous FRBs were detected at radio frequencies that match those used by cell phones, Wi-Fi, and similar devices. Consumers could potentially download a free smartphone app that would run in the background, monitoring appropriate frequencies and sending the data to a central processing facility.

    “An FRB in the Milky Way, essentially in our own back yard, would wash over the entire planet at once. If thousands of cell phones picked up a radio blip at nearly the same time, that would be a good sign that we’ve found a real event,” explains lead author Dan Maoz of Tel Aviv University.

    Finding a Milky Way FRB might require some patience. Based on the few, more distant ones, that have been spotted so far, Maoz and Loeb estimate that a new one might pop off in the Milky Way once every 30 to 1,500 years. However, given that some FRBs are known to burst repeatedly, perhaps for decades or even centuries, there might be one alive in the Milky Way today. If so, success could become a yearly or even weekly event.

    A dedicated network of specialized detectors could be even more helpful in the search for a nearby FRB. For as little as $10 each, off-the-shelf devices that plug into the USB port of a laptop or desktop computer can be purchased. If thousands of such detectors were deployed around the world, especially in areas relatively free from Earthly radio interference, then finding a close FRB might just be a matter of time.

    This work has been accepted for publication in the Monthly Notices of the Royal Astronomical Society and is available online.

    See the full article here .

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

     
  • richardmitnick 3:11 pm on January 4, 2017 Permalink | Reply
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    From NRAO: “Precise Location, Distance Provide Breakthrough in Study of Fast Radio Bursts” 

    NRAO Icon
    National Radio Astronomy Observatory

    NRAO Banner

    4 January 2017

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    Visible-light image of host galaxy.
    Credit: Gemini Observatory/AURA/NSF/NRC.

    For the first time, astronomers have pinpointed the location in the sky of a Fast Radio Burst (FRB), allowing them to determine the distance and home galaxy of one of these mysterious pulses of radio waves. The new information rules out several suggested explanations for the source of FRBs.

    “We now know that this particular burst comes from a dwarf galaxy more than three billion light-years from Earth,” said Shami Chatterjee, of Cornell University. “That simple fact is a huge advance in our understanding of these events,” he added. Chatterjee and other astronomers presented their findings to the American Astronomical Society’s meeting in Grapevine, Texas, in the scientific journal Nature, and in companion papers in the Astrophysical Journal Letters.

    Fast Radio Bursts are highly-energetic, but very short-lived (millisecond) bursts of radio waves whose origins have remained a mystery since the first one was discovered in 2007. That year, researchers scouring archived data from Australia’s Parkes Radio Telescope in search of new pulsars found the first known FRB — one that had burst in 2001.

    There now are 18 known FRBs. All were discovered using single-dish radio telescopes that are unable to narrow down the object’s location with enough precision to allow other observatories to identify its host environment or to find it at other wavelengths. Unlike all the others, however, one FRB, discovered in November of 2012 at the Arecibo Observatory in Puerto Rico, has recurred numerous times.

    NAIC/Arecibo Observatory, Puerto Rico, USA
    NAIC/Arecibo Observatory, Puerto Rico, USA

    The repeating bursts from this object, named FRB 121102 after the date of the initial burst, allowed astronomers to watch for it using the National Science Foundation’s (NSF) Karl G. Jansky Very Large Array (VLA), a multi-antenna radio telescope system with the resolving power, or ability to see fine detail, needed to precisely determine the object’s location in the sky.

    In 83 hours of observing time over six months in 2016, the VLA detected nine bursts from FRB 121102.

    “For a long time, we came up empty, then got a string of bursts that gave us exactly what we needed,” said Casey Law, of the University of California at Berkeley.

    “The VLA data allowed us to narrow down the position very accurately,” said Sarah Burke-Spolaor, of the National Radio Astronomy Observatory (NRAO) and West Virginia University.

    Using the precise VLA position, researchers used the Gemini North telescope in Hawaii to make a visible-light image that identified a faint dwarf galaxy at the location of the bursts. The Gemini observations also determined that the dwarf galaxy is more than 3 billion light-years from Earth.

    Gemini/North telescope at Mauna Kea, Hawaii, USA
    Gemini/North telescope at Mauna Kea, Hawaii, USA

    “Before we knew the distance to any FRBs, several proposed explanations for their origins said they could be coming from within or near our own Milky Way Galaxy. We now have ruled out those explanations, at least for this FRB,” said Shriharsh Tendulkar, of McGill University in Montreal, Canada.

    In addition to detecting the bright bursts from FRB 121102, the VLA observations also revealed an ongoing, persistent source of weaker radio emission in the same region.

    Next, a team of observers used the multiple radio telescopes of the European VLBI Network (EVN), along with the 1,000-foot-diameter William E. Gordon Telescope of the Arecibo Observatory, and the NSF’s Very Long Baseline Array (VLBA) to determine the object’s position with even greater accuracy.

    European VLBI
    European VLBI

    NRAO VLBA
    NRAO VLBA

    “These ultra high precision observations showed that the bursts and the persistent source must be within 100 light-years of each other,” said Jason Hessels, of the Netherlands Institute for Radio Astronomy and the University of Amsterdam.

    “We think that the bursts and the continuous source are likely to be either the same object or that they are somehow physically associated with each other,” said Benito Marcote, of the Joint Institute for VLBI ERIC, Dwingeloo, Netherlands.

    The top candidates, the astronomers suggested, are a neutron star, possibly a highly-magnetic magnetar, surrounded by either material ejected by a supernova explosion or material ejected by a resulting pulsar, or an active nucleus in the galaxy, with radio emission coming from jets of material emitted from the region surrounding a supermassive black hole.

    “We do have to keep in mind that this FRB is the only one known to repeat, so it may be physically different from the others,” cautioned Bryan Butler of NRAO.

    “Finding the host galaxy of this FRB, and its distance, is a big step forward, but we still have much more to do before we fully understand what these things are,” Chatterjee said.

    “This impressive result shows the power of several telescopes working in concert — first detecting the radio burst and then precisely locating and beginning to characterize the emitting source,” said Phil Puxley, a program director at the National Science Foundation that funds the VLA, VLBA, Gemini and Arecibo observatories. “It will be exciting to collect more data and better understand the nature of these radio bursts.”

    See the full article here .

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    The NRAO operates a complementary, state-of-the-art suite of radio telescope facilities for use by the scientific community, regardless of institutional or national affiliation: the Very Large Array (VLA), the Robert C. Byrd Green Bank Telescope (GBT), and the Very Long Baseline Array (VLBA)*.

    ALMA Array

    NRAO ALMA

    GBO radio telescope, Green Bank, West Virginia, USA
    GBO Radio Observatory telescope, Green Bank, West Virginia, USA, formerly supported by NSF, but now on its own

    NRAO VLA
    NRAO VLA

    The NRAO is building two new major research facilities in partnership with the international community that will soon open new scientific frontiers: the Atacama Large Millimeter/submillimeter Array (ALMA), and the Expanded Very Large Array (EVLA). Access to ALMA observing time by the North American astronomical community will be through the North American ALMA Science Center (NAASC).
    *The Very Long Baseline Array (VLBA) comprises ten radio telescopes spanning 5,351 miles. It’s the world’s largest, sharpest, dedicated telescope array. With an eye this sharp, you could be in Los Angeles and clearly read a street sign in New York City!

    Astronomers use the continent-sized VLBA to zoom in on objects that shine brightly in radio waves, long-wavelength light that’s well below infrared on the spectrum. They observe blazars, quasars, black holes, and stars in every stage of the stellar life cycle. They plot pulsars, exoplanets, and masers, and track asteroids and planets.

     
  • richardmitnick 8:19 am on November 19, 2016 Permalink | Reply
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    From Science Alert: “Astronomers have traced the source of the most powerful radio signal ever received from space” 

    ScienceAlert

    Science Alert

    18 NOV 2016
    PETER DOCKRILL

    It’s not coming from inside the Milky Way.

    1
    The intensity of FRB 150807 at different radio frequencies. Credit: Dr Vikram Ravi/Caltech and Dr Ryan Shannon/ICRAR-Curtin/CSIRO

    Scientists have observed the most powerful fast radio burst (FRB) ever – an intensely brilliant burst of radiation emanating from outside our own Milky Way galaxy.

    The signal, which researchers say travelled at least a billion light-years to reach Earth, only lasted for a fraction of a second, but the observation could help us understand more about the epic gaps that exist between galaxies, called the cosmic web.

    “FRBs are extremely short but intense pulses of radio waves, each only lasting about a millisecond,” says astrophysicist Ryan Shannon from Curtin University in Australia. “Some are discovered by accident and no two bursts look the same.”

    There’s a lot we still don’t understand about FRBs and where they come from, partly because we’ve so far witnessed very few of them.

    This new burst – called FRB 150807 – is just the 18th FRB detected to date since they were first discovered in 2001.

    But despite this apparent rarity, scientists actually think these intensely powerful but short phenomena are happening all the time – we just don’t notice them.

    “We estimate that there are between 2,000 and 10,000 FRBs occurring in the sky every day,” says one of the team, astronomer Vikram Ravi from Caltech.

    One of the difficulties with detecting FRBs is how quickly they flash, which makes it difficult for telescopes observing large portions of the sky to pinpoint where the bursts originate.

    But FRB 150807’s intense luminosity not only made it easier to help trace the burst’s likely origins – it also gave scientists new clues about the intergalactic matter the burst travelled through to get here.

    “This particular FRB is the first detected to date to contain detailed information about the cosmic web – regarded as the fabric of the Universe,” says Shannon.

    “[B]ut it is also unique because its travel path can be reconstructed to a precise line of sight and back to an area of space about a billion light years away that contains only a small number of possible home galaxies.”

    When FRBs travel through space, they pass through a range of matter – including gases, ionised particles, and magnetic fields – which can distort the radio wave on its path.

    But FRB 150807 – which was detected using the CSIRO’s Parkes Observatory in Australia – appeared to only be weakly distorted, which suggests that the space dust and magnetic fields throughout the cosmic web are less turbulent than the gas and other material in the Milky Way.

    2
    Australia’s Parkes radio telescope detected a fast radio burst while monitoring a nearby pulsar.
    Roger Ressmeyer / Corbis / VCG / Getty Images

    Thanks to the signal’s brightness, the team triangulated its origin to a small handful of galaxies, with the most likely candidate being a star system called VHS7.

    This galaxy is thought to be located between 3.2 and 6.5 billion light-years away, although the researchers acknowledge that they can’t be 100 percent certain that this is where the FRB hails from.

    And it’s also possible that the FRB could have come from a dim galaxy that we haven’t previously detected in sky surveys – but the team is convinced that wherever this distant galaxy is, it’s at least 1.5 billion light-years from Earth.

    While there’s still a lot we don’t know about these intense radio waves, FRB 150807’s stronger-than-usual signal at least should have cleared up any longstanding doubts as to whether FRBs actually emanate from outside the Milky Way – some scientists thought the signals could be explained by phenomena occurring inside our own galaxy.

    “I think this is laid to rest for the class of objects,” astronomer James M. Cordes from Cornell University, who wasn’t involved with the research, told Nadia Drake at National Geographic. “There may be one or two in the 18 published bursts that could still be in our galaxy, but the others could not.”

    And while we’ve still got our fair share of questions about what these FRBs are and what’s actually generating them, at least this new data gives us our clearest picture yet of these insanely powerful micro-events.

    “[FRB 150807] shows the promise of probing the large-scale structure of the Universe,” astrophysicist Duncan Lorimer from West Virginia University, who was not involved with this research, told Loren Grush at The Verge.

    “This particular source doesn’t solve the mystery of what [FRBs] are. But it gives us a great amount of hope for what [scientists] can do in the future.”

    The findings are reported in Science.

    See the full article here .

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  • richardmitnick 2:50 pm on August 25, 2016 Permalink | Reply
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    From JHU: “Can one cosmic enigma help solve another? Johns Hopkins researchers think so” 

    Johns Hopkins
    Johns Hopkins University

    8.24.16
    Arthur Hirsch

    1
    Image credit: VectaRay

    2
    A massive cluster of yellowish galaxies, seemingly caught in a red and blue spider web of eerily distorted background galaxies, makes for a spellbinding picture from the new Advanced Camera for Surveys aboard NASA’s Hubble Space Telescope. To make this unprecedented image of the cosmos, Hubble peered straight through the center of one of the most massive galaxy clusters known, called Abell 1689. The gravity of the cluster’s trillion stars — plus dark matter — acts as a 2-million-light-year-wide lens in space. This gravitational lens bends and magnifies the light of the galaxies located far behind it. Some of the faintest objects in the picture are probably over 13 billion light-years away (redshift value 6). Strong gravitational lensing as observed by the Hubble Space Telescope in Abell 1689 indicates the presence of dark matter. Credit: NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI),G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA. phys.org.

    Astrophysicists from Johns Hopkins University have proposed a clever new way of shedding light on the mysterious dark matter believed to make up most of the universe. The irony is they want to try to pin down the nature of this unexplained phenomenon by using another obscure cosmic emanation known as “fast radio bursts.”

    In a paper published today in Physical Review Letters, the team of astrophysicists argues that these extremely bright and brief flashes of radio-frequency radiation can provide clues about whether certain black holes are dark matter.

    Julian Muñoz, a Johns Hopkins graduate student and the paper’s lead author, said fast radio bursts, or FRBs, provide a direct and specific way of detecting black holes of a specific mass, which are the suspect dark matter.

    FRB Fast Radio Bursts from NAOJ Subaru
    FRB Fast Radio Bursts from NAOJ Subaru, Mauna Key, Hawaii, USA

    Muñoz wrote the paper along with Ely D. Kovetz, a post-doctoral fellow; Marc Kamionkowski, a professor in the Department of Physics and Astronomy; and Liang Dai, who completed his doctorate in astrophysics at Johns Hopkins last year. Dai is now a NASA Einstein Postdoctoral Fellow at the Institute for Advanced Study in Princeton, New Jersey.

    The paper builds on a hypothesis offered in a paper published this spring by Muñoz, Kovetz, and Kamionkowski, along with five Johns Hopkins colleagues. Also published in Physical Review Letters, that research made a speculative case that the collision of black holes detected early in the year by the Laser Interferometer Gravitational-Wave Observatory, or LIGO, was actually dark matter, a substance that makes up 85 percent of the mass of the universe.

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib
    Credit: MPI for Gravitational Physics/W.Benger-Zib
    LSC LIGO Scientific Collaboration
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    The earlier paper made what Kamionkowski called a “plausibility argument” that LIGO found dark matter. The study took as a point of departure the fact that the objects detected by LIGO fit within the predicted range of mass of so-called “primordial” black holes. Unlike black holes that formed from imploded stars, primordial black holes are believed to have formed from the collapse of large expanses of gas during the birth of the universe.

    The existence of primordial black holes has not been established with certainty, but they have been suggested before as a possible solution to the riddle of dark matter. With so little evidence of them to examine, the hypothesis had not gained a large following among scientists.

    The earlier paper made what Kamionkowski called a “plausibility argument” that LIGO found dark matter. The study took as a point of departure the fact that the objects detected by LIGO fit within the predicted range of mass of so-called “primordial” black holes. Unlike black holes that formed from imploded stars, primordial black holes are believed to have formed from the collapse of large expanses of gas during the birth of the universe.

    The LIGO findings, however, raised the prospect anew, especially as the objects detected in that experiment conform to the mass predicted for dark matter.

    The Johns Hopkins team calculated how often these primordial black holes would form binary pairs, and eventually collide. Taking into account the size and elongated shape believed to characterize primordial black hole binary orbits, the team came up with a collision rate that conforms to the LIGO findings.

    Key to the argument is that the black holes that LIGO detected fall within a range of 29 to 36 solar masses, meaning they are that many times greater than the mass of the sun. The new paper considers the question of how to test the hypothesis that dark matter consists of black holes of roughly 30 solar masses.

    That’s where the fast radio bursts come in. First observed only a few years ago, these flashes of radio frequency radiation emit intense energy, but last only fractions of a second. Their origins are unknown but are believed to lie in galaxies outside the Milky Way.

    If the speculation about their origins is true, Kamionkowski said, the radio waves would travel great distances before they’re observed on Earth, perhaps passing a black hole. According to Einstein’s theory of general relativity, the ray would be deflected when it passes a black hole. If it passes close enough, it could be split into two rays shooting off in the same direction—creating two images from one source.

    The new study shows that if the black hole has 30 times the mass of the Sun, the two images will arrive a few milliseconds apart. If 30-solar-mass black holes make up the dark matter, there is a chance that any given fast radio burst will be deflected in this way and followed in a few milliseconds by an echo.

    “The echoing of FRBs is a very direct probe of dark matter,” Muñoz said. “While gravitational waves might ‘indicate’ that dark matter is made of black holes, there are other ways to produce very-massive black holes with regular astrophysics, so it would be hard to convince oneself that we are detecting dark matter. However, gravitational lensing of fast radio bursts has a very unique signature, with no other astrophysical phenomenon that could reproduce it.”

    Kaimonkowski said that while the probability for any such FRB echo is small, “it is expected that several of the thousands of FRBs to be detected in the next few years will have such echoes … if black holes make up the dark matter.”

    So far, only about 20 fast radio bursts have been detected and recorded since 2001. The very sensitive instruments needed to detect them can look at only very small slices of the sky at a time, limiting the rate at which the bursts can be found. A new telescope expected to go into operation this year that seems particularly promising for spotting radio bursts is the Canadian Hydrogen Intensity Mapping Experiment. The joint project of the University of British Columbia, McGill University, the University of Toronto, and the Dominion Radio Astrophysical Observatory stands in British Columbia.

    “Once the thing is working up to their planned specifications, they should collect enough FRBs to begin the tests we propose,” said Kamionkowski, estimating results could be available in three to five years.

    See the full article here .

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    Johns Hopkins Campus

    The Johns Hopkins University opened in 1876, with the inauguration of its first president, Daniel Coit Gilman. “What are we aiming at?” Gilman asked in his installation address. “The encouragement of research … and the advancement of individual scholars, who by their excellence will advance the sciences they pursue, and the society where they dwell.”

    The mission laid out by Gilman remains the university’s mission today, summed up in a simple but powerful restatement of Gilman’s own words: “Knowledge for the world.”

    What Gilman created was a research university, dedicated to advancing both students’ knowledge and the state of human knowledge through research and scholarship. Gilman believed that teaching and research are interdependent, that success in one depends on success in the other. A modern university, he believed, must do both well. The realization of Gilman’s philosophy at Johns Hopkins, and at other institutions that later attracted Johns Hopkins-trained scholars, revolutionized higher education in America, leading to the research university system as it exists today.

     
  • richardmitnick 11:45 am on June 28, 2016 Permalink | Reply
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    From Nature: “Why ultra-powerful radio bursts are the most perplexing mystery in astronomy” 

    Nature Mag
    Nature

    28 June 2016
    Elizabeth Gibney

    1
    The Parkes telescope in Australia detected the first fast radio burst in 2001. Wayne England

    No astronomer had ever seen anything like it. No theorist had predicted it. Yet there it was — a 5-millisecond radio burst that had arrived on 24 August 2001 from an unknown source seemingly billions of light years away.

    “It was so bright, we couldn’t just dismiss it,” says Duncan Lorimer, who co-discovered the signal [1] in 2007 while working on archived data from the Parkes radio telescope in New South Wales, Australia. “But we didn’t really know what to do with it.”

    Such fleeting radio bursts usually came from pulsars — furiously rotating neutron stars whose radiation sweeps by Earth with the regularity of a lighthouse beam. But Lorimer, an astrophysicist at West Virginia University in Morgantown, saw this object erupt only once, and with more power than any known pulsar.

    He began to realize the significance of the discovery [1] only after carefully going over the data with his former adviser, Matthew Bailes, an astrophysicist at Swinburne University of Technology in Melbourne, Australia. If the source was really as far away as it seemed, it had released the energy of 500 million Suns in just a few milliseconds. “We became convinced it was something quite remarkable,” he says.

    But when no more bursts appeared, initial excitement turned to doubt. Radio astronomers have learnt to be sceptical of mysterious spikes in their detectors: the events can all too easily result from mobile-phone signals, stray radar probes, strange weather phenomena and instrumental glitches. Wider acceptance of what is now known as the Lorimer burst came only in the past few years, after observers working at Parkes and other telescopes spotted similar signals. Today, the 2001 event is recognized as the first in a new and exceedingly peculiar class of sources known as fast radio bursts (FRBs) — one of the most perplexing mysteries in astronomy.

    Whatever these objects are, recent observations suggest that they are common, with one flashing in the sky as often as every 10 seconds [2]. Yet they still defy explanation. Theorists have proposed sources such as evaporating black holes, colliding neutron stars and enormous magnetic eruptions. But even the best model fails to account for all the observations, says Edo Berger, an astronomer at Harvard University in Cambridge, Massachusetts, who describes the situation as “a lot of swirling confusion”.

    Clarity may come soon, however. Telescopes around the world are being adapted to look for the mysterious bursts. One of them, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) near Penticton in British Columbia, should see as many as a dozen FRBs per day when it comes online by the end of 2017.

    3
    CHIME

    “This area is set to explode,” says Bailes.

    Curiouser and curiouser

    Astronomers might have had more confidence in the Lorimer burst initially had it not been for a discovery in 2010 by Sarah Burke-Spolaor, who was then finishing her astrophysics PhD at Swinburne. Burke-Spolaor, now an astronomer at the US National Radio Astronomy Observatory in Socorro, New Mexico, was trawling through old Parkes data in search of more bursts when she turned up 16 signals that shook everyone’s confidence in the original [3].

    In most ways, these signals looked remarkably similar to the Lorimer event. They, too, showed ‘dispersion’, meaning that high-frequency waves appeared in the detectors a few hundred milliseconds before the low-frequency ones. This dispersion effect was the most important piece of evidence convincing Lorimer and Bailes that the original burst came from well beyond our Galaxy. Interstellar electrons in clouds of ionized gas are known to interact more with low-frequency waves than with high-frequency ones, which delays the low-frequency waves’ arrival at Earth ever so slightly, and stretches the signal (see ‘Flight delays‘). The delay in the Lorimer burst was so extensive that the wave had to have travelled through a lot of matter — much more than is in our Galaxy.

    4
    Nik Spencer/Nature; Source: Fig. 1 In Keane, E. F. et al. Nature 530, 453–456 (2016)

    Unfortunately for Lorimer and Bailes’ peace of mind, Burke-Spolaor’s signals also showed a crucial difference from the original: they seemed to pour in from everywhere, not just from where the telescope was pointing. Dubbed perytons, after a mythical winged creature that casts a human shadow, these bursts could have been caused by lightning, or some human-made source. But they were not extraterrestrial.

    Lorimer decided to postpone his research into FRBs for a while. “I didn’t yet have tenure,” he says, “so I had to go back and do more mainstream projects, just to keep my research moving.” Bailes and his team kept going, and upgraded the Parkes detector’s time and frequency resolution. In 2013, they turned up four new FRB candidates that resembled the Lorimer burst [4]. But some outsiders remained sceptical that the signals were really coming from space — not least because all the FRBs thus far had been seen by one team using one telescope. “I was desperate for someone else to find them somewhere else,” says Bailes.

    In 2014, his wish was finally granted. A team led by astronomer Laura Spitler at the Max Planck Institute for Radio Astronomy in Bonn, Germany, published their observations of a burst at the Arecibo Observatory in Puerto Rico5. “I was ridiculously overjoyed,” says Bailes.

    NAIC/Arecibo Observatory, Puerto Rico, USA
    NAIC/Arecibo Observatory, Puerto Rico, USA

    The Arecibo discovery convinced most people that FRBs were the real deal, says Emily Petroff, who is now an astrophysicist at the Netherlands Institute for Radio Astronomy in Dwingeloo. Yet, as long as the Burke-Spolaor signals went unexplained, they cast a shadow of doubt. “At any talks I would give,” says Petroff, “someone would say, ‘But what about perytons?’” So in 2015, while still a graduate student at Swinburne, she led a hunt to track down the source of perytons once and for all.

    First, Petroff and her team used the upgraded Parkes detector to pinpoint when the bursts were happening: at lunchtime. “Immediately I thought, ‘This isn’t weather’,” says Petroff. Then came another peryton at a suspiciously familiar radio frequency, which led the team to run experiments in the staff kitchen. Perytons, they discovered, were the result of scientists opening the microwave oven mid-flow. But the Lorimer event was in the clear: records showed that at the time of the burst, the telescope had been pointed in a direction that would have blocked any microwave signal from the kitchen [6].

    “So then I worried, maybe they’ve just got a different brand of microwave at Arecibo,” says Bailes, whose team at Parkes had, by then, racked up 14 separate bursts. He did not relax completely until later in 2015, when a burst was spotted at a third facility — the Green Bank Telescope in West Virginia.

    NRAO/GBT radio telescope, West Virginia, USA
    NRAO/GBT radio telescope, West Virginia, USA

    That burst had another quality that supported an extraterrestrial origin: its waves were rotated in a spiral pattern — which results from passing through a magnetic field — and were scattered as if they had emerged from a dense medium. “There’s no way that’s a microwave oven,” Bailes told himself.

    Bursts of inspiration

    But that still leaves the question of what the FRBs actually are. The extreme brevity of the signal, just 5 milliseconds, implied that the source must be a compact object no more than a few hundred kilometres across — a stellar-mass black hole, perhaps, or a neutron star, the compact core left over by a supernova. And the fact that Earth-based telescopes can detect the FRBs at all means that this compact source somehow puts out an immense amount of energy. But that still leaves a long list of candidates, from merging black holes to flares on magnetars: rare neutron stars with fields hundreds of millions of billions of times stronger than the Sun’s.

    An important clue arrived earlier this year when Spitler’s team reported that at least one FRB source repeats: data from Arecibo revealed a flurry of bursts over two months, some spaced just minutes apart [7]. That behaviour has been confirmed by the Green Bank telescope, which detects signals in a different frequency band8. Until then, each of the observed FRBs had been a one-off event, which hinted at cataclysmic explosions, or collisions in which the sources were destroyed. But a repeating FRB implies the existence of a source that survives the pulse event, says Petroff. And for that reason, she says, “I would assume it would be something to do with a neutron star” — one of the few known objects that can emit a pulse without self-destructing.

    Spitler agrees. As an example, she points to the Crab nebula: the result of a supernova explosion that was observed from Earth in 1054 and left behind a rapidly spinning pulsar surrounded by glowing gas.

    Supernova remnant Crab nebula. NASA/ESA Hubble
    Supernova remnant Crab nebula. NASA/ESA Hubble

    The Crab pulsar occasionally releases extremely bright and narrow radio flares, Spitler says. And if this nebula were in a distant galaxy and hugely boosted in energy, its emissions would look like FRBs.

    If one source repeats, Spitler says, the simplest interpretation is that they all do, but that other telescopes haven’t been sensitive enough — or lucky enough — to see the additional signals. Yet others think that perhaps only some are repeating. “I wouldn’t be surprised if we end up with two or three populations,” says Petroff.
    A long way home

    Another crucial question is how far away the FRBs are. The 20 bursts seen so far seem to be scattered randomly around the sky rather than being concentrated in the plane of the Galaxy, which suggests that their sources lie beyond the borders of the Milky Way.

    And yet to Avi Loeb, a physicist at Harvard University, such vast distances imply an implausibly large energy output. “If you want the burst to repeat, you won’t be able to destroy the source — therefore, it cannot release too much energy,” he says. “That puts a limit on how far away you can put it.” Perhaps, he says, the FRB sources are neutron stars in our own Galaxy, and the dispersion is mostly the result of still unknown electron clouds that blanket them.

    But others suggest that such a dense cloud in the Galaxy should be visible in other wavelengths. At the California Institute of Technology (Caltech) in Pasadena, astrophysicist Shri Kulkarni has scoured data from several telescopes for a galactic source and turned up nothing [9]. Kulkarni, who directs Caltech’s optical observatories, initially argued for galactic FRBs, and even made a US$1,000 bet on it with astronomer Paul Groot of Radboud University Nijmegen in the Netherlands. Now, he finds the evidence for extragalactic FRBs to be overwhelming, and has agreed to settle the bet — grudgingly. “I think I will pay him in $1 bills,” he says.

    5
    The black-hole collision that reshaped physics

    Still, Kulkarni hasn’t ruled out the possibility that the FRB sources lie in galaxies that are perhaps a billion light years away, rather than many billions. Such a distance would still require at least some of the signal dispersion to come from electron clouds in the host galaxy, he says. But closer FRBs would not have to be so energetic. “It takes them from being amazingly exotic, to just exotic,” he says.

    The answer could mean a great deal to observers. If the FRB signals have travelled through local plasma clouds, they could give weather reports from neighbouring galaxies. But if they are truly cosmological — coming from halfway across the visible Universe — they could solve a long-standing cosmic mystery.

    For decades, astronomers have known from observations of the early Universe that the cosmos should contain more everyday matter — the kind made up of electrons, protons and neutrons — than exists in the visible stars and galaxies. They suspect that it lies in the cold intergalactic medium, where it is effectively invisible. But now, for the first time, the dispersion of the FRB signals could enable them to measure the medium’s density in any given direction. “Then, we have essentially a surgical device to do intergalactic tomography,” says Kulkarni.

    Rapid-fire detection

    First, however, astronomers have to find a lot more FRBs and pin down their locations. “Until then, we are stumbling in the dark,” says Berger.

    One way to accomplish that is to extract the FRBs from radio-telescope data in real time, so that scientists at other observatories can observe the bursts in multiple wavelengths. Since last year, the Parkes team has been doing this by boosting the observatory’s in-house computing power, and scientists at Arecibo hope to follow suit this year. In February, the strategy seemed to be paying off when an independent team followed up within two hours of an FRB’s detection at Parkes. The team tentatively pinpointed the burst to a specific galaxy almost 6 billion light years away. Further observations cast doubt on that interpretation. But even so, says Lorimer, the method is sound and may pay off in the future.

    Others observers are putting their hopes in new telescopes. In 2014, astrophysicist Victoria Kaspi at McGill University in Montreal, Canada, submitted a proposal to adapt CHIME, which was originally designed to map the expansion of the Universe in its early years. “It became clear very quickly that it would be a fantastic FRB instrument,” says Kaspi. Although dish telescopes such as Arecibo can be highly sensitive, they observe only a single, tiny patch of sky at a time. CHIME, by contrast, consists of four 100-metre-long half-pipes dotted with antennas that can monitor much bigger stretches of sky in long lines. After undergoing testing and debugging, CHIME should see its first FRBs sometime next year, says Kaspi, ultimately finding more than a dozen per day.

    In Hoskinstown, Australia, meanwhile, Bailes and his colleagues are refurbishing the 1960s-vintage Molonglo Observatory Synthesis Telescope, turning it into an FRB observatory with a single half-pipe 16 times longer than CHIME’s, although one-quarter as wide.

    Molonglo Observatory Synthesis Telescope (MOST)
    U Sidney Molonglo Observatory Synthesis Telescope (MOST), Hoskinstown, Australia

    The team has already found three as-yet-unpublished FRBs with the facility working at only about 20% of its final sensitivity, says Bailes.

    Another strategy for locating the FRB sources is to work with existing facilities such as the Very Large Array: an ‘interferometer’ that uses the time difference between signals from 27 radio telescopes spaced across 36 kilometres of grassland near Socorro, New Mexico, to create a single, high-resolution image.

    NRAO/VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA
    NRAO/VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    Sometime in the next year or so, says Lorimer, the array could detect an FRB and locate its home galaxy. “Ultimately, that could settle a lot of arguments and bets,” he says.

    Kulkarni, meanwhile, is leading two projects. The first uses ten 5-metre-wide dishes in an array that can see and locate only super-bright FRBs, but that makes up for its low sensitivity by peering at a huge swathe of sky. The second takes the principle to the extreme, using 2 antennas spaced at observatories 450 kilometres apart that will see only the very brightest FRBs, but that are able to examine half the sky at once. That would enable it to catch the rare FRBs that presumably exist within our own Galaxy, but whose extreme brightness existing telescopes are not designed to see. “Most facilities would just discount it as interference,” says Kulkarni.

    If FRBs do turn out to come from cosmological distances, says Loeb, their identification would be a major breakthrough, potentially unravelling a new class of source that could be used to probe the Universe’s missing matter. But then, he says, FRBs could also be something that no one has thought of yet: “Nature is much more imaginative than we are.”

    References

    1. Lorimer, D. R., Bailes, M., McLaughlin, M. A., Narkevic, D. J. & Crawford, F. Science 318, 777–780 (2007).

    2. Champion, D. J. et al. Mon. Not. R. Astron. Soc. Lett. 460, L30–L34 (2016).

    3. Burke-Spolaor, S., Bailes, M., Ekers, R., Macquart, J.-P. & Crawford, F. III Astrophys. J. 727, 18 (2011).

    4. Thornton, D. et al. Science 341, 53–56 (2013).

    5. Spitler, L. G. et al. Astrophys. J. 790, 101 (2014).

    6. Petroff, E. et al. Mon. Not. R. Astron. Soc. 451, 3933–3940 (2015).

    7. Spitler, L. G. et al. Nature 531, 202–205 (2016).

    8. Scholz, P. et al. Preprint at http://arxiv.org/abs/1603.08880 (2016).

    9. Kulkarni, S. R., Ofek, E. O. & Neill, J. D. Preprint at http://arxiv.org/abs/1511.09137 (2015).

    See the full article here .

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    Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

     
  • richardmitnick 1:57 pm on April 4, 2016 Permalink | Reply
    Tags: , , , Fast Radio Bursts   

    From CfA: “Fast Radio Burst ‘Afterglow’ Was Actually a Flickering Black Hole” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    April 4, 2016
    Christine Pulliam
    Media Relations Manager
    Harvard-Smithsonian Center for Astrophysics
    617-495-7463

    NRAO/VLA
    NRAO/VLA

    Last February a team of astronomers reported detecting an afterglow from a mysterious event called a fast radio burst, which would pinpoint the precise position of the burst’s origin, a longstanding goal in studies of these mysterious events. These findings were quickly called into question by follow-up observations. New research by Harvard astronomers Peter Williams and Edo Berger shows that the radio emission believed to be an afterglow actually originated from a distant galaxy’s core and was unassociated with the fast radio burst.

    “Part of the scientific process is investigating findings to see if they hold up. In this case, it looks like there’s a more mundane explanation for the original radio observations,” says Williams.

    The new work has been accepted for publication in Astrophysical Journal Letters.

    As their name suggests, fast radio bursts (or FRBs) are brief yet powerful spurts of radio energy lasting only a few milliseconds. The first ones were only identified in 2007. Their source has remained a mystery.

    “We don’t even know if they come from inside our galaxy or if they’re extragalactic,” explains Berger.

    Most FRBs have been identified in archival data, making immediate follow-up impossible. The new event, FRB 150418, is only the second one to be identified in real time. Radio observations reported in Nature purportedly showed a fading radio afterglow associated with the FRB. That afterglow was used to link the FRB to a host galaxy located about 6 billion light-years from Earth.

    In late February and March of this year, Williams and Berger investigated the supposed host galaxy in detail using the NSF’s Jansky Very Large Array network of radio telescopes. The fantastic sensitivity of the VLA allowed the researchers to monitor the radio galaxy at the necessary cadence without having to disrupt the observatory’s regular schedule of operations.

    If the initial observations had been an afterglow, it should have completely faded away. Instead they found a persistent radio source whose strength varied randomly by a factor of three, often reaching levels that matched the initial brightness of the claimed afterglow. The initial study also saw this source, but unluckily missed any rebrightenings.

    “What the other team saw was nothing unusual,” states Berger. “The radio emission from this source goes up and down, but it never goes away. That means it can’t be associated with the fast radio burst.”

    The emission instead originates from an active galactic nucleus that is powered by a supermassive black hole. Dual jets blast outward from the black hole, and complex physical processes within those jets create a constant source of radio waves.

    The variations we see from Earth may be due to a process called “scintillation,” where interstellar gases make an intrinsically steady radio beacon appear to flicker, just like Earth’s atmosphere makes light from stars twinkle. The source itself might also be varying as the active galactic nucleus periodically gulps a little more matter and flares in brightness.

    While the link between the fast radio burst and a specific galaxy has vanished, the astronomers remain optimistic for future studies.

    “Right now the science of fast radio bursts is where we were with gamma-ray bursts 30 years ago. We saw these things appearing and disappearing, but we didn’t know what they were or what caused them,” says Williams.

    “Now we have firm evidence for the origins of both short and long gamma-ray bursts. With more data and more luck, I expect that we’ll eventually solve the mystery of fast radio bursts too,” he adds.

    See the full article here .

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

     
  • richardmitnick 12:30 pm on September 11, 2015 Permalink | Reply
    Tags: , , , Fast Radio Bursts   

    From CAASTRO: “Solution to FRB conundrum also reveals clues about their origin” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    11 September 2015

    Since first reported in 2007, the origin of the bright, millisecond-duration pulses known as Fast Radio Bursts (FRBs) has remained a mystery to astronomers. There have been more theories proposed to explain them than the 17 events so far detected. Where do they come from – our Solar System, our Galaxy, or beyond? The dispersion sweeps of FRBs (the delay of the pulse arrival time with wavelength caused by propagating through plasma in space) indicate that they have travelled through so much material on their way to Earth that they must be cosmological in origin. There just is not enough plasma in the interstellar medium of the Milky Way to explain their long dispersion sweeps.

    1
    Four recently detected “blitzars” (red stars) have revealed that these sources of fleeting radio bursts are much more distant than known pulsars (black dots) (Image: C. Ng/MPIfR)

    Adding to the mystery, CAASTRO PhD student Emily Petroff (Swinburne University) and colleagues analysed the distribution of FRB detections across the sky and reported (in their 2014 paper) that their rate is about four times higher at high Galactic latitudes than close to the Galactic plane. This result is doubly puzzling because (a) the distribution of extragalactic pulses should not be related to their position with respect to the Galactic disk and (b) the rate of pulses of Galactic origin should be higher closer to the Galactic plane, the exact opposite of what is observed.

    CAASTRO members Dr Jean-Pierre Macquart (Curtin University) and Prof Simon Johnston (CSIRO) now provide an explanation in their recent publication. Radio pulses received at the Earth have propagated through the turbulent interstellar medium of our own Galaxy irrespective of whether they were generated inside or outside of it. The density fluctuations in this medium can randomly amplify the amplitude of a pulse. This effect is equivalent to the Earth’s atmosphere causing an apparent twinkling of stars.

    The intensity fluctuations change both with time and with observing frequency; and the more material, the more quickly they change with frequency. At low Galactic latitudes, FRBs propagate through so much turbulent Galactic material that the intensity fluctuations change very rapidly with frequency – so much so that radio telescopes average over many tens to hundreds of intensity fluctuations over the observing band. When averaged across the bandwidth of the telescope, the intensity is very close to the mean intensity of the pulse. However, at high Galactic latitudes the FRB radiation is subject to only one or two intensity fluctuations across the telescope observing band, and the observed radiation can be either greatly diminished or enhanced.

    See the full article here .

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    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

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