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  • richardmitnick 9:24 am on March 1, 2019 Permalink | Reply
    Tags: , , , , , Gravitational wave astronomy, ,   

    From “Physics”: “Synopsis: How to Test a Space-Based Gravitational-Wave Detector” 

    Physics LogoAbout Physics

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    From “Physics”

    February 28, 2019
    Christopher Crockett

    Researchers propose a device to verify the performance of the laser-based equipment that will fly on the Laser Interferometer Space Antenna.

    ESA/NASA eLISA space based, the future of gravitational wave research

    The gold-platinum alloy cubes, of central importance to the upcoming LISA mission, have already been built and tested in the proof-of-concept LISA Pathfinder mission

    The European Space Agency is moving ahead with plans to launch a gravitational-wave detector called “LISA” into space. LISA, which stands for Laser Interferometer Space Antenna, will listen for gravitational waves that are currently undetectable from ground-based facilities such as the Laser Interferometer Gravitational-Wave Observatory. Catching these subtle spacetime ripples will require instrumentation with phenomenally stringent precision. Now, researchers have developed a device to test a core piece of LISA’s laser-based technology and ensure that it meets the requisite performance requirements.

    D. Penkert/Max Planck Institute for Gravitational Physics

    Max Planck Institute for Gravitational Physics

    The planned LISA detector consists of three spacecrafts flying in triangle formation. Incoming gravitational waves will change the 2.5 million kilometers between each spacecraft by a few trillionths of a meter. To track those changes, the spacecraft will look for phase shifts in the laser light they receive from their two companions, a feat requiring precise measuring instruments with exceptionally low noise and low distortion.

    To test the precision of LISA’s phase-shift-measuring hardware, Thomas Schwarze and colleagues at the Max Planck Institute for Gravitational Physics in Germany built and trialed a calibration device. Their device consists of three lasers whose beams interfere with each other in such a way that their phases—after being extracted by a prototype of LISA’s phase-measuring hardware—should cancel each other out. Any nonzero value reported reflects noise or distortion introduced by the phase-measuring hardware.

    Others have suggested using three-laser setups to test LISA’s detectors, but the team’s device introduces an order of magnitude less noise than other proposals. With further refinements to their setup—such as swapping out photodetectors for models with lower noise—the team envisions that they could reduce measurement noise further. Doing that, they say, could enable their setup to serve as a critical performance check for LISA’s hardware.

    This research is published in Physical Review Letters.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments (physics@aps.org).

  • richardmitnick 1:32 pm on February 2, 2019 Permalink | Reply
    Tags: , , , Big Bang Observer, , , , , Gravitational wave astronomy, Gravity is talking. Lisa will listen,   

    From Ethan Siegel: “Ask Ethan: How Can LISA, Without Fixed-Length Arms, Ever Detect Gravitational Waves?” 

    From Ethan Siegel

    LIGO, here on Earth, has exquisitely-precise distances its lasers travel. With three spacecrafts in motion, how could LISA work?

    Since it began operating in 2015, advanced LIGO has ushered in an era of a new type of astronomy: using gravitational wave signals. The way we do it, however, is through a very special technique known as laser interferometry. By splitting a laser and sending each half of the beam down a perpendicular path, reflecting them back, and recombining them, we can create an interference pattern. If the lengths of those paths change, the interference pattern changes, enabling us to detect those waves. And that leads to the best question I got about science during my recent Astrotour in Iceland, courtesy of Ben Turner, who asked:

    LIGO works by having these exquisitely precise lasers, reflected down perfectly length-calibrated paths, to detect these tiny changes in distance (less than the width of a proton) induced by a passing gravitational wave. With LISA, we plan on having three independent, untethered spacecrafts freely-floating in space. They’ll be affected by all sorts of phenomena, from gravity to radiation to the solar wind. How can we possibly get a gravitational wave signal out of this?

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger

    Gravity is talking. Lisa will listen. Dialogos of Eide

    ESA/eLISA the future of gravitational wave research

    Localizations of gravitational-wave signals detected by LIGO in 2015 (GW150914, LVT151012, GW151226, GW170104), more recently, by the LIGO-Virgo network (GW170814, GW170817). After Virgo came online in August 2018

    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    It’s a great question, and the toughest one posed to me all year thus far. Let’s explore the answer.

    3D rendering of the gravitational waves emitted from a binary neutron star system at merger. The central region (in density) is stretched by a factor of ~5 for better visibility. The orientation of the merger itself determines how the signal will be polarized. (AEI POTSDAM-GOLM)

    Since the dawn of time, humanity has been practicing astronomy with light, which has progressed from naked-eye viewing to the use of telescopes, cameras, and wavelengths that go far beyond the limits of human vision. We’ve detected cosmic particles from space in a wide variety of flavors: electrons, protons, atomic nuclei, antimatter, and even neutrinos.

    But gravitational waves are an entirely new way for humanity to view the Universe. Instead of some detectable, discrete quantum particle that interacts with another, leading to a detectable signal in some sort of electronic device, gravitational waves act as ripples in the fabric of space itself. With a certain set of properties, including:

    propagation speed,
    frequency, and

    they affect everything occupying the space that they pass through.

    Gravitational waves propagate in one direction, alternately expanding and compressing space in mutually perpendicular directions, defined by the gravitational wave’s polarization. Gravitational waves themselves, in a quantum theory of gravity, should be made of individual quanta of the gravitational field: gravitons. (M. PÖSSEL/EINSTEIN ONLINE)

    When one of these gravitational waves passes through a LIGO-like detector, it does exactly what you might suspect. The gravitational wave, along the direction it propagates at the speed of gravity (which equals the speed of light), doesn’t affect space at all. Along the plane perpendicular to its propagation, however, it alternately causes space to expand and contract in mutually perpendicular directions. There are multiple types of polarization that are possible:

    “plus” (+) polarization, where the up-down and left-right directions expand and contract,
    “cross” (×) polarization, where the left-diagonal and right-diagonal directions expand and contract,
    or “circularly” polarized waves, similar to way light can be circularly polarized; this is a different parameterization of plus and cross polarizations.

    Whatever the physical case, the polarization is determined by the nature of the source.

    When a wave enters a detector, any two perpendicular directions will be compelled to contract and expand, alternately and in-phase, relative to one another. The amount that they contract or expand is related to the amplitude of the wave. The period of the expansion and contraction is determined by the frequency of the wave, which a detector of a specific arm length (or effective arm length, where there are multiple reflections down the arms, as in the case of LIGO) will be sensitive to.

    With multiple such detectors in a variety of orientations to one another in three-dimensional space, the location, orientation, and even polarization of the original source can be reconstructed. By using the predictive power of Einstein’s General Relativity and the effects of gravitational waves on the matter-and-energy occupying the space they pass through, we can learn about events happening all across the Universe.

    LIGO and Virgo have discovered a new population of black holes with masses that are larger than what had been seen before with X-ray studies alone (purple). This plot shows the masses of all ten confident binary black hole mergers detected by LIGO/Virgo (blue), along with the one neutron star-neutron star merger seen (orange). LIGO/Virgo, with the upgrade in sensitivity, should detect multiple mergers every week. (LIGO/VIRGO/NORTHWESTERN UNIV./FRANK ELAVSKY)

    But it’s only due to the extraordinary technical achievement of these interferometers that we can actually make these measurements. In a terrestrial, LIGO-like detector, the distances of the two perpendicular arms are fixed. Laser light, even if reflected back-and-forth along the arms thousands of times, will eventually see the two beams come back together and construct a very specific interference pattern.

    If the noise can be minimized below a certain level, the pattern will hold absolutely steady, so long as no gravitational waves are present.

    If, then, a gravitational wave passes through, and one arm contracts while the other expands, the pattern will shift.

    When the two arms are of exactly equal length and there is no gravitational wave passing through, the signal is null and the interference pattern is constant. As the arm lengths change, the signal is real and oscillatory, and the interference pattern changes with time in a predictable fashion. (NASA’S SPACE PLACE)

    By measuring the amplitude and frequency at which the pattern shifts, the properties of a gravitational wave can be reconstructed. By measuring a coincident signal in multiple such gravitational wave detectors, the source properties and location can be reconstructed as well. The more detectors with differing orientations and locations are present, the better-constrained the properties of the gravitational wave source will be.

    This is why adding the Virgo detector to the twin LIGO detectors in Livingston and Hanford enabled a far superior reconstruction of the location of gravitational wave sources. In the future, additional LIGO-like detectors in Japan and India will allow scientists to pinpoint gravitational waves in an even superior fashion.

    But there’s a limit to what we can do with detectors like this. Seismic noise from being located on the Earth itself limits how sensitive a ground-based detector can be. Signals below a certain amplitude can never be detected. Additionally, when light signals are reflected between mirrors, the noise generated by the Earth accumulates cumulatively.

    The fact that the Earth itself exists in the Solar System, even if there were no plate tectonics, ensures that the most common type of gravitational wave events — binary stars, supermassive black holes, and other low-frequency sources (taking 100 seconds or more to oscillate) — cannot be seen from the ground. Earth’s gravitational field, human activity, and natural geological processes means that these low-frequency signals cannot be practically seen from Earth. For that, we need to go to space.

    And that’s where LISA comes in.

    The sensitivities of a variety of gravitational wave detectors, old, new, and proposed. Note, in particular, Advanced LIGO (in orange), LISA (in dark blue), and BBO (in light blue). LIGO can only detect low-mass and short-period events; longer-baseline, lower-noise observatories are needed for more massive black holes. (MINGLEI TONG, CLASS.QUANT.GRAV. 29 (2012) 155006)

    LISA is the Laser Interferometer Space Antenna. In its current design, it consists of three dual-purpose spacecrafts, separated in an equilateral triangle configuration by roughly 5,000,000 kilometers along each laser arm.

    Inside each spacecraft, there are two free-floating cubes that are shielded by the spacecraft itself from the effects of interplanetary space. They will remain at a constant temperature, pressure, and will be unaffected by the solar wind, radiation pressure, or the bombardment of micrometeorites.

    By carefully measuring the distances between pairs of cubes on different spacecrafts, using the same laser interferometry technique, scientists can do everything that multiple LIGO detectors do, except for these long-period gravitational waves that only LISA is sensitive to. Without the Earth to create noise, it seems like an ideal setup.

    The primary scientific goal of the Laser Interferometer Space Antenna (LISA) mission is to detect and observe gravitational waves from massive black holes and galactic binaries with periods in the range of a tens of seconds to a few hours. This low-frequency range is inaccessible to ground-based interferometers because of the unshieldable background of local gravitational noise arising from atmospheric effects and seismic activity. (ESA-C. VIJOUX)

    But even without the terrestrial effects of human activity, seismic noise, and being deep within Earth’s gravitational field, there are still sources of noise that LISA must contend with. The solar wind will strike the detectors, and the LISA spacecrafts must be able to compensate for that. The gravitational influence of other planets and solar radiation pressure will induce tiny orbital changes relative to one another. Quite simply, there is no way to hold the spacecract at a fixed, constant distance of exactly 5 million km, relative to one another, in space. No amount of rocket fuel or electric thrusters will be able to maintain that exactly.

    Remember: the goal is to detect gravitational waves — themselves a tiny, minuscule signal — over and above the background of all this noise.

    The three LISA spacecraft will be placed in orbits that form a triangular formation with center 20° behind the Earth and side length 5 million km. This figure is not to scale. (NASA)

    So how does LISA plan to do it?

    The secret is in these gold-platinum alloy cubes. In the center of each optical system, a solid cube that’s 4 centimeters (about 1.6″) on each side floats freely in the weightless conditions of space. While external sensors monitor the solar wind and solar radiation pressure, with electronic sensors compensating for those extraneous forces, the gravitational forces from all the known bodies in the Solar System can be calculated and anticipated.

    As the spacecrafts, and the cubes, move relative to one another, the lasers adjust in a predictable, well-known fashion. So long as they continue to reflect off of the cubes, the distances between them can be measured.

    The gold-platinum alloy cubes, of central importance to the upcoming LISA mission, have already been built and tested in the proof-of-concept LISA Pathfinder mission

    ESA/LISA Pathfinder

    It’s not a matter of keeping the distances fixed and measuring a tiny change due to a passing wave; it’s a matter of understanding exactly how the distances will behave over time, accounting for them, and then looking for the periodic departures from those measurements to a high-enough precision. LISA won’t hold the three spacecrafts in a fixed position, but will allow them to adjust freely as Einstein’s laws dictate. It’s only because gravity is so well-understood that the additional signal of the gravitational waves, assuming the wind and radiation from the Sun is sufficiently compensated for, can be teased out.

    The proposed ‘Big Bang Observer’ would take the design of LISA, the Laser Interferometer Space Antenna, and create a large equilateral triangle around Earth’s orbit to get the longest-baseline gravitational wave observatory ever. (GREGORY HARRY, MIT, FROM THE LIGO WORKSHOP OF 2009, LIGO-G0900426)

    If we want to go even farther, we have dreams of putting three LISA-like detectors in an equilateral triangle around different points in Earth’s orbit: a proposed mission called Big Bang Observer (BBO). While LISA can detect binary systems with periods ranging from minutes to hours, BBO will be able to detect the grandest behemonths of all: supermassive binary black holes anywhere in the Universe, with periods of years.

    If we’re willing to invest in it, space-based gravitational wave observatories could allow us to map out all of the most massive, densest objects located throughout the entire Universe. The key isn’t holding your laser arms fixed, but simply in knowing exactly how, in the absence of gravitational waves, they’d move relative to one another. The rest is simply a matter of extracting the signal of each gravitational wave out. Without the Earth’s noise to slow us down, the entire cosmos is within our reach.

    See the full article here .


    Please help promote STEM in your local schools.

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 2:32 pm on December 19, 2018 Permalink | Reply
    Tags: , , , , Gravitational wave astronomy, , What LIGO Teaches Us About Black Holes   

    From Sky & Telescope: “What LIGO Teaches Us About Black Holes” 

    SKY&Telescope bloc

    From Sky & Telescope

    December 18, 2018
    Camille M. Carlisle

    The rising count of gravitational-wave events is giving us a new look at a once-invisible population of black holes.

    Now iconic imsge of two black holes prepare to merge in this artist’s illustration.
    LIGO / Caltech / MIT / Aurore Simonnet(Sonoma State)

    This artist’s conception portrays two neutron stars at the moment of collision. New observations confirm that colliding neutron stars probably produce short gamma-ray bursts. Dana Berry / SkyWorks Digital, Inc.

    Two weeks ago, scientists announced the detection of four black hole mergers, discovered thanks to the undulations they created in the fabric of spacetime. These latest events bring the tally of such smashups to 10. (An 11th is the famed double neutron star collision.)

    Now that we’ve entered the double digits for gravitational-wave discoveries, I’d like to stop and take a look at what these detections are revealing as a group. We’re nowhere near the illuminating statistical power brought by thousands of examples, as we are with exoplanets, but we can still sketch out an intriguing picture.

    Black holes are simple creatures; their two defining characteristics are their spin and mass. Astrophysicists measure black hole spin as a fraction of the theoretical maximum, which depends on the object’s mass and some other numbers. The values range from 0 (not spinning) to 1.

    A binary black hole system involves three spins: each individual black hole’s rotation, plus the two objects’ revolution around each other. These spins don’t necessarily line up. Think of two tops, spiraling in toward each other. The tops can stand straight up, their axes perfectly perpendicular to the tabletop. But they can also lean at various angles, roll on their sides, or even rotate backwards compared to the direction of the circuit each top traces around its partner.

    The same holds true for black holes. With current detector sensitivities, it’s difficult for the LIGO and Virgo teams to pinpoint the individual spins of the binary members that unite. But they can make some estimates, and the spin of the created black hole is fairly clear.

    Since the first gravitational-wave detections began piling up, I’ve been watching the spin measurements with growing fascination. Maya Fishbach (University of Chicago) and her colleagues had predicted that a black hole made by the merger of two others would spin at a rate that’s roughly 70% of its maximum — regardless of the parent objects’ masses and spins. One after another, each LIGO/Virgo detection has confirmed this prediction.

    What’s equally interesting, though, is that none of the original binary members appear to have spins this high. In the reanalysis recently released, the teams calculated each merging black hole’s spin. Only two events — GW151226 and GW170729 — involved objects with any detectable spins; the rest are basically zero. (The zeros include the parent black holes of GW170104, at least one of which researchers had thought spun backwards. The new analysis, taking better account of detector noise, revises that inference.)

    The caveat here is that the spins are measured in terms of how tilted they are compared to the binary’s orbital plane. It’s possible that the binary black holes might be whirling at wonky angles, unseen. But the researchers suspect this isn’t merely a matter of tilt hiding the rotation; the black holes really do have lower spins.

    I reached out to Fishbach for help understanding what these numbers mean. It comes down to origins, she explains. If the binary members really do spin slowly or not at all, then we can essentially rule out the scenario in which the LIGO/Virgo pairs all contain black holes formed from previous mergers. In other words, we are likely watching the collisions of first-generation black holes, made from stars.

    The masses support this conclusion, she adds. Above a mass of about 45 Suns there should be a gap, because the stars that are big enough to create black holes in this range instead obliterate themselves in a particularly destructive kind of blast that doesn’t make a black hole. The biggest binary black hole LIGO and Virgo have detected is approximately 50 Suns — potentially problematic for a supernova creation, but not indubitably in the no-man’s-land. If in the future LIGO and Virgo detect binary black holes in this forbidden zone, then it would be clear evidence of a second-generation black hole.

    We’re still unable to say much about how the binaries paired up to begin with. GW151226 and GW170729, the only two events with clearly spinning members, involved black holes that rotate in the same direction as their orbit around each other. That might indicate that each pair was born as a couple, instead of joining up later in life: We’d naïvely expect all three spins in the binary to line up if the black holes formed from a binary star system, whereas the black holes might be misaligned if they paired up after their creation, perhaps by meeting in the center of a globular star cluster. However, astronomers do debate this simplistic picture, since supernovae or binary interactions could knock the resulting black holes askew. That insight will have to wait for the future.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Sky & Telescope magazine, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

  • richardmitnick 2:26 pm on December 14, 2018 Permalink | Reply
    Tags: A Jet from Neutron Star Merger GW170817, , , , , , , Gravitational wave astronomy,   

    From AAS NOVA: ” A Jet from Neutron Star Merger GW170817″ 


    From AAS NOVA

    14 December 2018
    Kerry Hensley

    This artist’s impression of a black hole that formed after two neutron stars collided shows an accretion disk and a narrow jet. [NASA/CXC/M.Weiss]

    Just last year, the three observatories of the Laser Interferometer Gravitational-Wave Observatory (LIGO)–Virgo Collaboration detected the gravitational-wave signature of two neutron stars colliding. What can we learn from the months of observations made since?

    On 17 August, 2017, LIGO detected this “chirp” as two neutron stars spiraled inward and collided. This brief gravitational-wave blip, known as GW170817, has been followed up with months of multiwavelength observations. [LSC/Alex Nitz]

    When Worlds Collide

    Immediately following the detection of gravitational-wave event GW170817, teams of astronomers around the world rushed to pinpoint and characterize the electromagnetic radiation from the source.

    These early observations were hugely important for validating our understanding of what happens when neutron stars collide, but the work didn’t end there; in the months that followed, repeated measurements of the flux across the electromagnetic spectrum have provided us with the tools to probe what happened in the aftermath of the merger.

    These late-time observations should allow us to distinguish between two competing post-merger scenarios, in which the resultant relativistic jet either pushes past the previously ejected material surrounding the remnant (the “jet-dominated outflow” model) or fails to escape the slow-moving shroud of material (the “cocoon-dominated outflow” model) and is choked.

    Radio spectral indices from 6 to 10 months post merger. Combining all the radio data gives a spectral index of -0.53. The black line shown for reference is the radio-to-X-ray spectral index measurement. [Mooley et al. 2018]

    Tuning in to GW170817

    In order to characterize the nature of the outflow and determine which scenario describes GW170817, a team led by Kunal Mooley (National Radio Astronomy Observatory/Caltech) analyzed the decline of GW170817’s radio emission over time. The authors combined data from multiple radio sources — MeerKAT, Very Large Array (VLA), Giant Metrewave Radio Telescope (uGMRT), and the Australia Telescope Compact Array (ATCA) — to cover the radio emission from 0.65 to 12 GHz.

    SKA Meerkat telescope, 90 km outside the small Northern Cape town of Carnarvon, SA

    NRAO/Karl V Jansky Expanded Very Large Array, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    Giant Metrewave Radio Telescope, an array of thirty telecopes, located near Pune in India

    CSIRO Australia Compact Array, six radio telescopes at the Paul Wild Observatory, is an array of six 22-m antennas located about twenty five kilometres (16 mi) west of the town of Narrabri in Australia.

    After steadily rising for 5–6 months after the event, the radio emission peaked and quickly began to decline, making the transition from rising to falling in just a few weeks. The authors focused on two important features of the radio light curve: how rapidly the flux density decreases after the peak (the power-law decay index) and how “sharp” the peak of the light curve is.

    Radio data used in this study. All measurements have been scaled to 3 GHz. The black line is the best-fit model. [Mooley et al. 2018]

    Jet vs. Cocoon

    Models tell us that if GW170817’s jet were choked by a slow-moving cocoon of material, the radio observations would reveal a power-law decay index of -0.88. If instead the jet punches free of the material as in the jet-dominated outflow model, its flux density would decrease much more rapidly, exhibiting a power-law decay index of -2.17.
    So which model do the radio observations of GW170817 support? All of the post-peak data are well-described by a single power-law decay with an index of -2.4. This strongly supports the jet model over the cocoon model, and it suggests that the majority of the energy in the post-merger outflow is carried away by the jet.

    The sharpness of the light-curve peak is dependent upon the viewing angle and the width of the jet. Based on a simple jet model, the authors find that the jet is likely very narrow (with an opening angle of less than 10°) and the viewing angle is less than 28°. Future modeling will explore the effects that structure in the jet can have on how sharply peaked the radio light curve is and further our understanding of these highly energetic collisions.


    “A Strong Jet Signature in the Late-time Light Curve of GW170817,” K. P. Mooley et al 2018 ApJL 868 L11.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition


    AAS Mission and Vision Statement

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

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

    Adopted June 7, 2009

  • richardmitnick 4:21 pm on December 5, 2018 Permalink | Reply
    Tags: Gravitational wave astronomy,   

    From Pennsylvania State University: “LIGO supercomputer upgrade will speed up groundbreaking astrophysics research” 

    Penn State Bloc

    From Pennsylvania State University

    Gravitational wave astronomy is used to detect events such as binary star mergers, like the one depicted here. Image: Bangalore Sathyaprakash

    December 04, 2018

    In 2016, an international team of scientists found definitive evidence — tiny ripples in space known as gravitational waves — to support one of the last remaining untested predictions of Einstein’s theory of general relativity. The team used the Laser Interferometer Gravitational-Wave Observatory (LIGO), which has since made several gravitational wave discoveries. Each discovery was possible in part because of a global network of supercomputer clusters, one of which is housed at Penn State. Researchers use this network, known as the LIGO Data Grid, to analyze the gravitational wave data.

    Penn State recently invested in an upgrade to its portion of the data grid that will roughly quadruple the cluster’s capacity for conducting cutting-edge astronomy and astrophysics research. The new cluster, 192 servers working in tandem, is administered by the Institute for CyberScience (ICS). Bangalore Sathyaprakash, professor of astronomy and astrophysics and Elsbach Professor of Physics; and Chad Hanna, associate professor of physics and astronomy and astrophysics, and ICS co-hired faculty member, are the primary researchers who will be using the new system with their research team and collaborators.

    Speeding up faculty and student research

    “At Penn State we’re involved in all aspects of gravitational wave astronomy, which we use to learn about the universe,” said Sathyaprakash. “Until the discovery of gravitational waves, the only way we could observe the universe was using light, radio waves or gamma rays, which all belong to the electromagnetic spectrum. Gravitational waves allow us to create a complementary picture of the universe and reveal processes and phenomena that might not otherwise be revealed through electromagnetic observation.”

    The new cluster will vastly increase the speed at which researchers can complete analysis, according to Chad Hanna. He and colleagues recently finished the first study that used data housed on Penn State’s LIGO cluster. The team designed an experiment to quantify the number of binary black holes in the universe that have less mass than the Sun, which may have implications for the amount of dark matter in the universe.

    “Our first study that solely used the Penn State LIGO cluster took 12 weeks,” said Hanna. “If we were to complete that same investigation on the upgraded cluster today, it would only take three weeks.”

    The upgrade boosts the cluster from 1,152 compute cores to 4,608 cores, which will allow more researchers to use the system simultaneously. For reference, this is roughly equivalent to more than 1,000 desktop computers working in unison.

    “I’m most excited about the extra machines,” said Ryan Magee, graduate student in physics. “It allows for multiple analyses to run at once without much bottlenecking.”

    Magee plans to use the cluster to search for sub-solar mass compact objects in the universe, he said, because “they are not produced by stellar mechanisms, so it would be a hint of new physics.”

    Researchers at all levels will be using the new resource, including undergraduate students like Phoebe McClincy, a sophomore studying astronomy and astrophysics, and a Millennium Scholar. McClincy was first exposed to gravitational wave research as a high school student attending a Penn State summer camp led by Hanna.

    “During that summer camp I was actually afforded the opportunity to visit the cluster, and I remember thinking it was really cool and fascinating to see the other side of the computer,” said McClincy, now a member of Hanna’s research team. “I’ve always thought tech like this is amazing, so I can’t wait to see what can be done now that it will be even more advanced.”

    Building capacity for future LIGO discoveries

    The first iteration of LIGO’s observatories collected data from 2002 to 2010 but did not detect any gravitational waves. Upgrading the observatories to their current state, known as Advanced LIGO, greatly increased their detection capabilities, and, as a result, the system has detected six gravitational wave events since 2016.

    Sathyaprakash said there are plans to continue enhancing the detection capabilities of gravitational wave observatories, which will pose both opportunities and challenges for researchers.

    “When advanced LIGO reaches its design sensitivity, we will observe binary black hole collisions as far as tens of billions of light years and binary neutron star mergers billions of light years away. With the construction in the 2030s of new detectors that are 10 times more sensitive than the current ones, we will be able to observe the entire universe in gravitational waves for black holes and most of the universe for neutron stars,” he said.

    Coming with that will be challenges in collecting, storing and analyzing huge amounts of data. It has taken between one and three months to analyze each gravitational wave detected to date.

    “With advanced LIGO we expect to observe one event every day or every other day, this will offer a huge computational challenge, and so every bit helps,” he said. “With this new LIGO cluster, what we’ve done is to secure enough resources to be completely independent in doing our analyses. ICS and Penn State are enabling this challenging science. Without this new cluster, we would be very severely hampered from doing the science that we want to do.”

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger

    ESA/eLISA the future of gravitational wave research

    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

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

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

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

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  • richardmitnick 8:11 am on August 11, 2018 Permalink | Reply
    Tags: , , , , , Gravitational wave astronomy,   

    From Ethan Siegel: “What Happens When Planets, Stars And Black Holes Collide?” 

    From Ethan Siegel
    Aug 10, 2018

    Two neutron stars colliding, which is the primary source of many of the heaviest periodic table elements in the Universe. About 3-5% of the mass gets expelled in such a collision; the rest becomes a single black hole.Dana Berry, SkyWorks Digital, Inc.

    The Universe as we know it has been around for nearly 14 billion years: plenty of time for gravity to pull matter into clusters, clumps, and collapsed objects. By the present day, the Universe is filled with planets, stars, galaxies, and even larger structures, all bound together against the backdrop of the expanding Universe.

    But things aren’t so clean and neat. As large as space is, there are literally trillions of objects in our galaxy, moving on timescales of billions of years. Some of the systems that form will have multiple objects in them, and collisions between them aren’t just likely, they’re inevitable. Whenever a collision or merger occurs, it forever changes what we’re left with. Here’s the cosmic story of what happens.

    When an object collides with a planet, it can kick up debris and lead to the formation of nearby moons. This is where Earth’s Moon came from, and also where it’s thought that Mars’ and Pluto’s moons arose from as well.NASA/JPL-Caltech.

    Planet-planet collisions. Early on in the Solar System, there were likely more than eight planets. There may have been a fifth gas giant out between Jupiter and Neptune; our best simulations indicate that it got ejected. But in the inner Solar System, we believe there was a Mars-sized world that collided with a young Earth, giving rise to an enormous cloud of debris that coalesced to create our Moon. The giant impact hypothesis has been thoroughly validated by a number of lines of evidence, including by the lunar samples we brought back to Earth from the Apollo missions.

    Rather than the two Moons we see today, a collision followed by a circumplanetary disk may have given rise to three moons of Mars, where only two survive today.Labex UnivEarths / Université Paris Diderot

    Beyond that, we also have some pretty good evidence that Mars’ moons were created, along with a third, larger one that’s since fallen back down onto the red planet, by a large proto-planetary collision, too.

    From all the simulations we’ve performed and the evidence we’ve accumulated, rocky planets of comparable sizes collide quite frequently in the early stages of a solar system’s creation. When they smash together, they create a single, larger planet, but with a cloud of debris that coalesces to form one nearby, large satellite and up to several smaller, more distant satellites. The Pluto-Charon system is a spectacular example of this, with four additional, outer, tumbling moons.

    The inspiral and merger scenario for brown dwarfs as well-separated as these two are would take a very long time due to gravitational waves. But collisions are quite likely. Just as red stars colliding produce blue straggler stars, brown dwarf collisions can make red dwarf stars. Over long enough timescales, these ‘blips’ of light may become the only sources illuminating the Universe.Melvyn B. Davies, Nature 462, 991-992 (2009)

    Brown dwarf collisions. Want to make a star, but you didn’t accumulate enough mass to get there when the gas cloud that created you first collapsed? There’s a second chance available to you! Brown dwarfs are like very massive gas giants, more than a dozen times as massive as Jupiter, that experience strong enough temperatures (about 1,000,000 K) and pressures at their centers to ignite deuterium fusion, but not hydrogen fusion. They produce their own light, they remain relatively cool, and they aren’t quite true stars. Ranging in mass from about 1% to 7.5% of the Sun’s mass, they are the failed stars of the Universe.

    But if you have two in a binary system, or two in disparate systems that collide by chance, all of that can change in a flash.

    These are the two brown dwarfs that make up Luhman 16, and they may eventually merge together to create a star.NASA/JPL/Gemini Observatory/AURA/NSF

    The reason for that is that very little about the compositions of these failed stars changes over time. They’re still made of 70-75% hydrogen each, and when they merge together, they still have all of that unburned fuel. If the total mass of the merged object now exceeds that critical threshold of 0.075 solar masses, the Universe will have created a new star! With this much mass in a single object, temperatures will rise past that critical 4,000,000 K to ignite hydrogen fusion. Instead of two brown dwarfs, we’ll have created a red dwarf: a bona fide M-class star. The nearby binary brown dwarf system Luhman 16, just 6.5 light years away, is tantalizingly close to having the exact parameters necessary to eventually become a red dwarf star.

    A selection of the globular cluster Terzan 5, a unique link to the Milky Way’s past. Incredibly old stars can be found within globular clusters, relics of some of the first ‘bursts’ of star formation to occur in our vicinity of the Universe. The occasional blue star seen within, however, tells us that there’s more to the story.NASA/ESA/Hubble/F. Ferraro

    Two stars colliding. Stars come in a wide variety of masses, with the lower-mass ones appearing redder, cooler, and burning through their fuel more slowly, while the higher-mass ones are bluer, hotter, and live for shorter amounts of time. When we look at star clusters, we can get an idea of how old they are by viewing the highest-mass stars that are left, since the most massive ones die the fastest.

    Yet when we look at some of the oldest star clusters of all, we find a population of stars that are bluer and hotter than ought to be present. They simply don’t match up with the rest of the stars that are around. These blue straggler stars are real, though, and they have a fantastic explanation: stellar collisions.

    Blue straggler stars, circled in the inset image, are formed when older stars or even stellar remnants merge together. After the last stars have burned out, the same process could bring light to the Universe, albeit briefly, once again.NASA, ESA, W. Clarkson (Indiana University and UCLA), and K. Sahu (STScl)

    Take any two (or more) stars and merge them together, and they’ll make a single, more massive star. Even when all that remain are the redder stars, say one of 0.7 solar masses and one of 0.8 solar masses, if they merge together, they can create a bluer (1.5 solar mass) star, even if the star cluster they exist in is too old to have a 1.5 solar mass star remaining.

    Blue stragglers are common in the dense environments of globular clusters, and demonstrate that even long after all the stars as massive as the Sun have burned out, we will still create new ones simply by gravitational mergers.

    The ultimate event for multi-messenger astronomy would be a merger of two white dwarfs that were close enough to Earth to detect neutrinos, light, and gravitational waves all at once. These objects are known to produce Type Ia supernovae.NASA, ESA, and A. Feild (STScI)

    White dwarf collisions. So, your normal, main-sequence star lived through its life, burning through all the fuel it will ever burn. As a remnant, its core became a white dwarf star: the future fate of our Sun. And then, floating out there in the depths of interstellar space, it collided with another white dwarf star.


    White dwarf-white dwarf collisions lead to Type Ia supernovae, and may yet be the most common way these cataclysms originate. When such an event occurs, the stars undergo a runaway fusion reaction, giving off a tremendous amount of light and energy, and utterly destroy both white dwarfs that gave rise to the event. This is the one type of collision that completely destroys both the colliding objects.

    See https://sciencesprings.wordpress.com/2017/10/20/from-ucsc-neutron-stars-gravitational-waves-and-all-the-gold-in-the-universe/

    Artist’s illustration of two merging neutron stars. Binary neutron star systems inspiral and merge as well, but the closest orbiting pair we’ve found won’t merge until nearly 100 million years have passed. LIGO will likely find many others before that.NSF / LIGO / Sonoma State University / A. Simonnet

    Neutron star collisions. Arising from even more massive stars than those that give rise to white dwarfs, neutron stars can often exist in multi-star systems. Recently, we’ve observed two neutron stars in a binary system inspiraling and merging: a kilonova event. When this occurs, a large burst of energy is given off, and a substantial fraction of mass is ejected. The critical 2017 event that occurred marked the first time that the same object was observed in both gravitational waves and electromagnetic radiation.

    The masses of stellar remnants are measured in many different ways. This graphic shows the masses for black holes detected through electromagnetic observations (purple); the black holes measured by gravitational-wave observations (blue); neutron stars measured with electromagnetic observations (yellow); and the masses of the neutron stars that merged in an event called GW170817, which were detected in gravitational waves (orange). The result of the merger was a neutron star, briefly, that swiftly became a black hole. LIGO-Virgo/Frank Elavsky/Northwestern

    If the two neutron stars merge together to create a single one, they either:

    become a more massive neutron star (if their total is less than ~2.5 solar masses),
    become a neutron star that spins and then collapses to a black hole (if the total is under 2.75 solar masses),
    or collapses directly to a black hole (if the total mass is over 2.75 solar masses).

    Over the coming years and decades, we hope to observe many of these events to refine the accuracy of these statements even further.

    Black hole collisions. Merge a black hole with a black hole, and you get an even more massive black hole. But there’s a catch: up to around 5% of that mass gets lost! The first merging black hole pair we ever saw was a 36 solar mass black hole merging with a 29 solar mass black hole. But it created a black hole whose final mass was just 62 solar masses! A total of three suns worth of mass was simply lost.

    Where did it go? It was emitted in the form of gravitational radiation: the gravitational waves that LIGO detected from over a billion light years away. For a brief moment lasting less than a second, two merging black holes can emit more energy into the observable Universe than all the stars within it combined.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Other collisions are expected, such as black hole-neutron star, neutron star-white dwarf, neutron star-normal star, or even black hole-normal star. Objects like active galaxies or microquasars may be triggered by a black hole devouring stars or gas clouds. We have yet to observe any of these collisions as they happen, however, although we have discovered a candidate for a Thorne-Zytkow object: a neutron star at the core of a red giant star. Space may be a very big place, but it’s far from empty. Particularly within galaxies and star/globular clusters, the density of planets, stars, and stellar remnants are tremendous, and collisions such as these are inevitable. Whatever the consequences may be, it’s up to us to find out!

    See the full article here .


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    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 7:17 am on August 11, 2018 Permalink | Reply
    Tags: , , , , , Gravitational wave astronomy,   

    From Center For Astrophysics: “Spitzer Infrared Observations of a Gravitational Wave Source – a Binary Neutron Star Merger” 

    Harvard Smithsonian Center for Astrophysics

    From Center For Astrophysics

    GW170817 is the name given to a gravitational wave signal seen by the LIGO and Virgo detectors on 17 August 2017.

    See https://sciencesprings.wordpress.com/2017/10/20/from-ucsc-neutron-stars-gravitational-waves-and-all-the-gold-in-the-universe/

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Lasting for about 100 seconds, the signal was produced by the merger of two neutron stars. The observation was then confirmed – the first time this has happened for gravitational waves – by observations with light waves: the preceding five detections of merging black holes did not have (and were not expected to have) any detectable electromagnetic signals. The light from the neutron star merger is produced by the radioactive decay of atomic nuclei created in the event. (Neutron star mergers do more than just produce optical light, by the way: they are also responsible for making most of the gold in the universe.) Numerous ground-based optical observations of the merger concluded that the decaying atomic nuclei fall into at least two groups, a rapidly evolving and fast moving one composed of elements less massive than Lanthanide Series elements, and one that is more slowly evolving and dominated by heavier elements.

    Ten days after the merger, the continuum emission peaked at infrared wavelengths with a temperature of approximately 1300 kelvin, and continued to cool and dim. The Infrared Array Camera (IRAC) on the Spitzer Space Telescope observed the region around GW170817 for 3.9 hours in three epochs 43, 74 and 264 days after the event (SAO is the home of IRAC PI Fazio and his team). The shape and evolution of the emission reflect the physical processes at work, for example, the fraction of heavy elements in the ejecta or the possible role of carbon dust. Tracking the flux over time enables the astronomers to refine their models and understanding of what happens when neutron stars merge.

    A team of CfA astronomers, Victoria Villar, Philip Cowperthwaite, Edo Berger, Peter Blanchard, Sebastian Gomez, Kate Alexander, Tarraneh Eftekhari, Giovanni Fazio, James Guillochon, Joe Hora, Matthew Nicholl, and Peter Williams and two colleagues participated in an effort to measure and interpret the infrared observations. The source was extremely faint and moreover lies close to a very bright point source. Using a novel algorithm to prepare and subtract the IRAC images to eliminate the constant-brightness objects, the team was able to spot the merger source clearly in the first two epochs, although it was fainter than was predicted by the models by more than about a factor of two. It had dimmed beyond detection by the third epoch. However the rate of dimming and the infrared colors are consistent with models; at these epochs the material had cooled down to about 1200 kelvin. The team suggests several possible reasons for the surprising faintness, including possible transformation of the ejecta into a nebulous phase and notes that the new dataset will help refine the models.

    The scientists conclude by emphasizing that future binary star merger detections (an improved LISA will begin observing again in 2019) will similarly benefit from infrared observations, and that characterization of the infrared will enable more accurate determination of the nuclear decay processes underway. Their current paper, moreover, shows that Spitzer should be able to spot binary mergers as far away as four hundred million light-years, about the distance that the improved LISA should be able to probe.

    Spitzer Space Telescope Infrared Observations of the Binary Neutron Star Merger GW170817
    The Astrophysical Journal Letters

    See the full article here .


    Please help promote STEM in your local schools.

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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 9:22 am on May 28, 2018 Permalink | Reply
    Tags: , , , , , Gravitational wave astronomy, Things that go bump in the detector: dealing with glitches in LIGO data   

    From astrobites: “Things that go bump in the detector: dealing with glitches in LIGO data” 

    Astrobites bloc

    From astrobites

    Title: Parameter Estimation and Model Selection of Gravitational Wave Signals Contaminated by Transient Detector Noise Glitches
    Authors: Jade Powell, no affiliation listed
    Status: arXiv preprint

    On August 17, 2017, the Laser Interferometer Gravitational-Wave Observatory (LIGO) made a historic detection of a gravitational wave signal from a merging neutron star binary.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    This detection was interesting for many reasons, not least of all because it was the first multi-messenger detection of both gravitational waves and electromagnetic radiation from the same event.

    Because gravitational wave detectors are so complicated and sensitive, they are vulnerable to transient, short-duration instrumental or environmental noise, called glitches. An interesting feature of GW170817 was that it occurred during a glitch in one of the detectors (Livingston), causing the automated system to veto the data from that detector and preventing the neutron star merger signal from being distributed immediately.

    Figure 1. Characteristic examples of the types of transient features that can occur in the LIGO data due to detector glitches. From left to right: a “blip” glitch, a “whistle” glitch and a “scattered light” glitch (which occurs due to scattered laser light in the detector). Figure 1 in paper.

    Fortunately, the signal was long and the glitch was short, meaning that the glitch could easily be removed from the data. But we may not be so lucky next time! For example, if the signal itself is not well understood or even completely unknown, we need to know how to deal with detector glitches.

    See the full article here .


    Please help promote STEM in your local schools.
    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

  • richardmitnick 11:58 am on April 27, 2018 Permalink | Reply
    Tags: 000 Black Hole Mergers A Year..., , , , , , , Gravitational wave astronomy, LIGO Misses 100   

    From Ethan Siegel: “LIGO Misses 100,000 Black Hole Mergers A Year…” 

    Ethan Siegel
    Apr 26, 2018

    …but if a radical new idea comes to fruition, maybe we can find them after all.

    The General Relativity picture of curved spacetime, where matter and energy determine how these systems evolve over time, has made successful predictions that no other theory can match, including for the existence and properties of gravitational waves: ripples in spacetime. (LIGO)

    After decades of planning, building, prototyping, upgrading, and calibrating, the Laser Interferometer Gravitational-wave Observatory (LIGO) finally achieved it’s ultimate goal just a little over two years ago: the first direct detection of gravitational waves.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Since 2015, LIGO has seen the ripples in spacetime or gravitational waves from no fewer than six separate events. Five (and possibly more) black hole-black hole pairs and one neutron star-neutron star inspiral-and-merger had their unique, unmistakable signatures detected by multiple gravitational wave detectors simultaneously, enabling us to confirm a key prediction of Einstein’s General Relativity that had eluded experimentalists for a century. But in theory, black hole-black hole mergers should occur every few minutes somewhere in the Universe; LIGO is missing more than 100,000 of these annually. For the first time, a team of scientists may just have figured out how to detect all the mergers that LIGO is currently missing.

    When two black holes orbit one another, they’re both radiating energy away, and doing so constantly. According to Einstein’s General Relativity, any time a mass moves and accelerates through a changing gravitational field, itself changing its momentum, it has to emit radiation inherent to space itself: gravitational radiation. Each of the two masses in their gravitational dance emits them, and part of the theoretical work behind LIGO was calculating in excruciating detail what the magnitude, duration, amplitude, and frequencies of gravitational waves would be emitted for any two arbitrary black hole masses and orientations.

    The gravitational wave signal from the first pair of detected, merging black holes from the LIGO collaboration. Although a large amount of information can be extracted, no images or the presence/absence of an event horizon can be gleaned. (B. P. Abbott et al., (LIGO Scientific Collaboration and Virgo Collaboration), Physical Review Letters 116, 061102 (2016))

    It was only from that sort of template creation and matching that we were able to detect these events at all. It was incredibly successful as well; the confirmations, when they occurred, were spectacular in their agreement with the predictions. But LIGO is only sensitive to those final few moments of a merger, where the amplitude of these gravitational waves is sufficient to contract-and-expand these enormous arms by a tiny fraction of a wavelength of light, enough so that after a thousand reflections, the light shifts by a barely-perceptible amount.

    The masses of stellar remnants are measured in many different ways. This graphic shows the masses for black holes detected through electromagnetic observations (purple); the black holes measured by gravitational-wave observations (blue); neutron stars measured with electromagnetic observations (yellow); and the masses of the neutron stars that merged in an event called GW170817, which were detected in gravitational waves (orange).(LIGO-Virgo/Frank Elavsky/Northwestern)

    Over the time that LIGO’s been operational, it has seen six robust events: about 0.001% of the total number of mergers expected in the Universe. Sure, most of them are anticipated to be far away, oriented non-optimally, or to occur between low-mass, low-amplitude black holes. There’s a good reason LIGO hasn’t seen them; the current generation of ground-based gravitational wave detectors are severely limited in sensitivity and range.

    Illustrated here is the range of Advanced LIGO and its capability of detecting merging black holes. Merging neutron stars may have only one-tenth the range and 0.1% the volume, but if neutron stars are abundant enough, LIGO may have a chance at those, too. (LIGO Collaboration / Amber Stuver / Richard Powell / Atlas of the Universe)

    But with 100,000 black hole-black hole mergers occurring annually in the observable Universe, these gravitational wave signals are constantly passing through Earth and our detectors. They’re simply below the detectable threshold, meaning that they have an impact on an apparatus like LIGO or Virgo, but not one we can pull out and identify as a unique, unambiguous gravitational wave event. You may not be able to detect them individually, but with so many of them occurring, it may be possible to extract an aggregate signal. Rather than an individual chirp, these combined mergers should produce a gravitational wave background hum. These mergers are quick and shouldn’t overlap with one another, meaning that the background should look like a series of disconnected signals that are too faint to detect.

    The noise (top), the strain (middle), and the reconstructed signal (bottom) in a bona fide gravitational wave event seen in all three detectors. For most of the mergers, they’re simply too far away for their amplitude in order for LIGO/Virgo to detect them. (The LIGO Scientific Collaboration and The Virgo Collaboration)

    That is, they’re too faint to detect individually! But if you know what your signal looks like and you both build up enough statistics and apply enough computational power, you just might be able to tease it out of the noise. It won’t tell you how many individual events you have, but it can tell you how many total events there are over the time you observe it. In other words, rather than say, “we expect 100,000 of these a year,” we can actually observe the overall black hole-black hole merger rate in the Universe. More importantly, we can learn, for the first time, what the total number-and-mass density of black holes in the Universe actually is.

    A map of the 7 million second exposure of the Chandra Deep Field-South. This region shows hundreds of supermassive black holes, each one in a galaxy far beyond our own. There should be hundreds of thousands of times as many stellar-mass black holes; we’re just waiting for the capability of detecting them. (NASA/CXC/B. Luo et al., 2017, ApJS, 228, 2)

    NASA/Chandra X-ray Telescope

    In a new paper entitled Optimal Search for an Astrophysical Gravitational-Wave Background [PHYSICAL REVIEW X], scientists Rory Smith and Eric Thrane propose to do exactly that. For every problem like this, there’s a computationally optimal way to approach it, and Smith and Thrane worked hard to come up with the answer. There are a number of interesting things the authors deduce they can learn from this computational exercise:

    You can derive the most sensitive possible search for this background of unresolved black holes.
    You can learn about the populations of black holes at earlier times in the Universe compared to the modern, nearby Universe.
    You can combine the results of this search with both confirmed detections and marginal, candidate detections to remove the bias inherent in seeing the largest-amplitude signals the most easily.
    If it’s successful, this method can be generalized to neutron stars, non-merging masses, and even potentially the gravitational wave background left over from the Universe’s birth.

    The final prediction of cosmic inflation is the existence of primordial gravitational waves. It is the only one of inflation’s predictions to not be verified by observation… yet. (National Science Foundation (NASA, JPL, Keck Foundation, Moore Foundation, related) — Funded BICEP2 Program; modifications by E. Siegel)

    Best of all, their conclusions are incredibly optimistic for what the future holds for applying this supercomputer-based technique to the LIGO and Virgo data sets. Writing in the journal Physical Review X, they state:

    “…Preliminary estimates suggest that advanced detectors, operating at design sensitivity, can detect a stochastic background from binary black holes in about 1 day. These estimates rely on extrapolation using Gaussian mixture modeling of our Bayesian evidence distributions. The next step is to carry out a mock data challenge in which we demonstrate the safety and efficacy of the search using ≈1 day of design sensitivity Monte Carlo data. Such a demonstration would allow us to verify the extrapolations made here with a modest computational cost ≈500 000 core hours….”

    In other words, they plan to demonstrate that this signal can be extracted from a noisy background by simulating it, blinding the computer, and then proving that the supercomputer, alone, can identify it.

    By simulating both data sets with (left) and without (right) a signal, the researchers anticipate that a realistic astrophysical background should be detected with a supercomputer time of approximately 20 hours, compared to more than year using existing methods. (R. Smith and E. Thrane, Phys. Rev. X 8, 021019 (2018)[link is above])

    The era of gravitational wave astronomy is now upon us. Owing to the incredible capabilities of ground-based detectors like LIGO and Virgo, we have now detected six robust events over the past 2+ years, from black holes to merging neutron stars. But huge questions surrounding the black holes in the Universe, such as how many there are, what their masses are early on compared to today, and what percent of the Universe is made of black holes, still remain to be answered. The direct efforts have gotten us a very long way, but the indirect signals matter, too, and can potentially teach us even more if we’re willing to make inferences that follow the physics and math. LIGO may be missing upwards of 100,000 black hole-black hole mergers a year. But with this new proposed technique, we might finally learn what else is out there, with the potential to apply this to neutron stars, non-merging black holes, and even the leftover ripples from our cosmic birth. It’s an incredible time to be alive.

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 4:04 pm on April 14, 2018 Permalink | Reply
    Tags: , , , , , Gravitational wave astronomy, , ,   

    From Monash U and OzGrav via Science Alert: “We Could Detect Black Hole Collisions All The Time With This Amazing New Method” 

    Monash Univrsity bloc

    Monash University



    Science Alert

    (LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)

    13 APR 2018

    Black holes could be making cataclysmic collisions across the Universe every few minutes. Unfortunately, the aftermath is too faint to alert our current detection technology.

    But a clever new technique could allow us to “hear” these collisions by finding their signals in the background static that LIGO-Virgo’s detectors are picking up all the time.

    Even though we humans can’t hear any sounds coming from space, the gravitational wave signal of two black holes or neutron stars colliding can be translated into a sound wave.

    This has been done for the six confirmed gravitational wave signals picked up since that first groundbreaking detection in 2015.

    But these events are much more frequent than we have detected to date, according to Eric Thrane and Rory Smith of the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) and Monash University.

    Both of these researchers participated in that first discovery, as well as last year’s jaw-dropping neutron star collision.

    UC Santa Cruz

    UC Santa Cruz


    A UC Santa Cruz special report

    Tim Stephens

    Astronomer Ryan Foley says “observing the explosion of two colliding neutron stars” [see https://sciencesprings.wordpress.com/2017/10/17/from-ucsc-first-observations-of-merging-neutron-stars-mark-a-new-era-in-astronomy ]–the first visible event ever linked to gravitational waves–is probably the biggest discovery he’ll make in his lifetime. That’s saying a lot for a young assistant professor who presumably has a long career still ahead of him.

    The first optical image of a gravitational wave source was taken by a team led by Ryan Foley of UC Santa Cruz using the Swope Telescope at the Carnegie Institution’s Las Campanas Observatory in Chile. This image of Swope Supernova Survey 2017a (SSS17a, indicated by arrow) shows the light emitted from the cataclysmic merger of two neutron stars. (Image credit: 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

    Carnegie Institution Swope telescope at Las Campanas, Chile, 100 kilometres (62 mi) northeast of the city of La Serena. near the north end of a 7 km (4.3 mi) long mountain ridge. Cerro Las Campanas, near the southern end and over 2,500 m (8,200 ft) high, at Las Campanas, Chile

    A neutron star forms when a massive star runs out of fuel and explodes as a supernova, throwing off its outer layers and leaving behind a collapsed core composed almost entirely of neutrons. Neutrons are the uncharged particles in the nucleus of an atom, where they are bound together with positively charged protons. In a neutron star, they are packed together just as densely as in the nucleus of an atom, resulting in an object with one to three times the mass of our sun but only about 12 miles wide.

    “Basically, a neutron star is a gigantic atom with the mass of the sun and the size of a city like San Francisco or Manhattan,” said Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz.

    These objects are so dense, a cup of neutron star material would weigh as much as Mount Everest, and a teaspoon would weigh a billion tons. It’s as dense as matter can get without collapsing into a black hole.


    Like other stars, neutron stars sometimes occur in pairs, orbiting each other and gradually spiraling inward. Eventually, they come together in a catastrophic merger that distorts space and time (creating gravitational waves) and emits a brilliant flare of electromagnetic radiation, including visible, infrared, and ultraviolet light, x-rays, gamma rays, and radio waves. Merging black holes also create gravitational waves, but there’s nothing to be seen because no light can escape from a black hole.

    Foley’s team was the first to observe the light from a neutron star merger that took place on August 17, 2017, and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Now, for the first time, scientists can study both the gravitational waves (ripples in the fabric of space-time), and the radiation emitted from the violent merger of the densest objects in the universe.

    The UC Santa Cruz team found SSS17a by comparing a new image of the galaxy N4993 (right) with images taken four months earlier by the Hubble Space Telescope (left). The arrows indicate where SSS17a was absent from the Hubble image and visible in the new image from the Swope Telescope. (Image credits: Left, Hubble/STScI; Right, 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

    It’s that combination of data, and all that can be learned from it, that has astronomers and physicists so excited. The observations of this one event are keeping hundreds of scientists busy exploring its implications for everything from fundamental physics and cosmology to the origins of gold and other heavy elements.

    A small team of UC Santa Cruz astronomers were the first team to observe light from two neutron stars merging in August. The implications are huge.


    It turns out that the origins of the heaviest elements, such as gold, platinum, uranium—pretty much everything heavier than iron—has been an enduring conundrum. All the lighter elements have well-explained origins in the nuclear fusion reactions that make stars shine or in the explosions of stars (supernovae). Initially, astrophysicists thought supernovae could account for the heavy elements, too, but there have always been problems with that theory, says Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz.

    The violent merger of two neutron stars is thought to involve three main energy-transfer processes, shown in this diagram, that give rise to the different types of radiation seen by astronomers, including a gamma-ray burst and a kilonova explosion seen in visible light. (Image credit: Murguia-Berthier et al., Science)

    A theoretical astrophysicist, Ramirez-Ruiz has been a leading proponent of the idea that neutron star mergers are the source of the heavy elements. Building a heavy atomic nucleus means adding a lot of neutrons to it. This process is called rapid neutron capture, or the r-process, and it requires some of the most extreme conditions in the universe: extreme temperatures, extreme densities, and a massive flow of neutrons. A neutron star merger fits the bill.

    Ramirez-Ruiz and other theoretical astrophysicists use supercomputers to simulate the physics of extreme events like supernovae and neutron star mergers. This work always goes hand in hand with observational astronomy. Theoretical predictions tell observers what signatures to look for to identify these events, and observations tell theorists if they got the physics right or if they need to tweak their models. The observations by Foley and others of the neutron star merger now known as SSS17a are giving theorists, for the first time, a full set of observational data to compare with their theoretical models.

    According to Ramirez-Ruiz, the observations support the theory that neutron star mergers can account for all the gold in the universe, as well as about half of all the other elements heavier than iron.


    Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity, but until recently they were impossible to observe. LIGO’s extraordinarily sensitive detectors achieved the first direct detection of gravitational waves, from the collision of two black holes, in 2015. Gravitational waves are created by any massive accelerating object, but the strongest waves (and the only ones we have any chance of detecting) are produced by the most extreme phenomena.

    Two massive compact objects—such as black holes, neutron stars, or white dwarfs—orbiting around each other faster and faster as they draw closer together are just the kind of system that should radiate strong gravitational waves. Like ripples spreading in a pond, the waves get smaller as they spread outward from the source. By the time they reached Earth, the ripples detected by LIGO caused distortions of space-time thousands of times smaller than the nucleus of an atom.

    The rarefied signals recorded by LIGO’s detectors not only prove the existence of gravitational waves, they also provide crucial information about the events that produced them. Combined with the telescope observations of the neutron star merger, it’s an incredibly rich set of data.

    LIGO can tell scientists the masses of the merging objects and the mass of the new object created in the merger, which reveals whether the merger produced another neutron star or a more massive object that collapsed into a black hole. To calculate how much mass was ejected in the explosion, and how much mass was converted to energy, scientists also need the optical observations from telescopes. That’s especially important for quantifying the nucleosynthesis of heavy elements during the merger.

    LIGO can also provide a measure of the distance to the merging neutron stars, which can now be compared with the distance measurement based on the light from the merger. That’s important to cosmologists studying the expansion of the universe, because the two measurements are based on different fundamental forces (gravity and electromagnetism), giving completely independent results.

    “This is a huge step forward in astronomy,” Foley said. “Having done it once, we now know we can do it again, and it opens up a whole new world of what we call ‘multi-messenger’ astronomy, viewing the universe through different fundamental forces.”


    Neutron stars
    A team from UC Santa Cruz was the first to observe the light from a neutron star merger that took place on August 17, 2017 and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO)

    Graduate students and post-doctoral scholars at UC Santa Cruz played key roles in the dramatic discovery and analysis of colliding neutron stars.Astronomer Ryan Foley leads a team of young graduate students and postdoctoral scholars who have pulled off an extraordinary coup. Following up on the detection of gravitational waves from the violent merger of two neutron stars, Foley’s team was the first to find the source with a telescope and take images of the light from this cataclysmic event. In so doing, they beat much larger and more senior teams with much more powerful telescopes at their disposal.

    “We’re sort of the scrappy young upstarts who worked hard and got the job done,” said Foley, an untenured assistant professor of astronomy and astrophysics at UC Santa Cruz.

    David Coulter, graduate student

    The discovery on August 17, 2017, has been a scientific bonanza, yielding over 100 scientific papers from numerous teams investigating the new observations. Foley’s team is publishing seven papers, each of which has a graduate student or postdoc as the first author.

    “I think it speaks to Ryan’s generosity and how seriously he takes his role as a mentor that he is not putting himself front and center, but has gone out of his way to highlight the roles played by his students and postdocs,” said Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz and the most senior member of Foley’s team.

    “Our team is by far the youngest and most diverse of all of the teams involved in the follow-up observations of this neutron star merger,” Ramirez-Ruiz added.

    Charles Kilpatrick, postdoctoral scholar

    Charles Kilpatrick, a 29-year-old postdoctoral scholar, was the first person in the world to see an image of the light from colliding neutron stars. He was sitting in an office at UC Santa Cruz, working with first-year graduate student Cesar Rojas-Bravo to process image data as it came in from the Swope Telescope in Chile. To see if the Swope images showed anything new, he had also downloaded “template” images taken in the past of the same galaxies the team was searching.

    Ariadna Murguia-Berthier, graduate student

    “In one image I saw something there that was not in the template image,” Kilpatrick said. “It took me a while to realize the ramifications of what I was seeing. This opens up so much new science, it really marks the beginning of something that will continue to be studied for years down the road.”

    At the time, Foley and most of the others in his team were at a meeting in Copenhagen. When they found out about the gravitational wave detection, they quickly got together to plan their search strategy. From Copenhagen, the team sent instructions to the telescope operators in Chile telling them where to point the telescope. Graduate student David Coulter played a key role in prioritizing the galaxies they would search to find the source, and he is the first author of the discovery paper published in Science.

    Matthew Siebert, graduate student

    “It’s still a little unreal when I think about what we’ve accomplished,” Coulter said. “For me, despite the euphoria of recognizing what we were seeing at the moment, we were all incredibly focused on the task at hand. Only afterward did the significance really sink in.”

    Just as Coulter finished writing his paper about the discovery, his wife went into labor, giving birth to a baby girl on September 30. “I was doing revisions to the paper at the hospital,” he said.

    It’s been a wild ride for the whole team, first in the rush to find the source, and then under pressure to quickly analyze the data and write up their findings for publication. “It was really an all-hands-on-deck moment when we all had to pull together and work quickly to exploit this opportunity,” said Kilpatrick, who is first author of a paper comparing the observations with theoretical models.

    César Rojas Bravo, graduate student

    Graduate student Matthew Siebert led a paper analyzing the unusual properties of the light emitted by the merger. Astronomers have observed thousands of supernovae (exploding stars) and other “transients” that appear suddenly in the sky and then fade away, but never before have they observed anything that looks like this neutron star merger. Siebert’s paper concluded that there is only a one in 100,000 chance that the transient they observed is not related to the gravitational waves.

    Ariadna Murguia-Berthier, a graduate student working with Ramirez-Ruiz, is first author of a paper synthesizing data from a range of sources to provide a coherent theoretical framework for understanding the observations.

    Another aspect of the discovery of great interest to astronomers is the nature of the galaxy and the galactic environment in which the merger occurred. Postdoctoral scholar Yen-Chen Pan led a paper analyzing the properties of the host galaxy. Enia Xhakaj, a new graduate student who had just joined the group in August, got the opportunity to help with the analysis and be a coauthor on the paper.

    Yen-Chen Pan, postdoctoral scholar

    “There are so many interesting things to learn from this,” Foley said. “It’s a great experience for all of us to be part of such an important discovery.”

    Enia Xhakaj, graduate student


    Scientific Papers from the 1M2H Collaboration

    Coulter et al., Science, Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source

    Drout et al., Science, Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis

    Shappee et al., Science, Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger

    Kilpatrick et al., Science, Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger

    Siebert et al., ApJL, The Unprecedented Properties of the First Electromagnetic Counterpart to a Gravitational-wave Source

    Pan et al., ApJL, The Old Host-galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational-wave Source

    Murguia-Berthier et al., ApJL, A Neutron Star Binary Merger Model for GW170817/GRB170817a/SSS17a

    Kasen et al., Nature, Origin of the heavy elements in binary neutron star mergers from a gravitational wave event

    Abbott et al., Nature, A gravitational-wave standard siren measurement of the Hubble constant (The LIGO Scientific Collaboration and The Virgo Collaboration, The 1M2H Collaboration, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration, The DLT40 Collaboration, The Las Cumbres Observatory Collaboration, The VINROUGE Collaboration & The MASTER Collaboration)

    Abbott et al., ApJL, Multi-messenger Observations of a Binary Neutron Star Merger


    Watch Ryan Foley tell the story of how his team found the neutron star merger in the video below. 2.5 HOURS.

    Press releases:

    UC Santa Cruz Press Release

    UC Berkeley Press Release

    Carnegie Institution of Science Press Release

    LIGO Collaboration Press Release

    National Science Foundation Press Release

    Media coverage:

    The Atlantic – The Slack Chat That Changed Astronomy

    Washington Post – Scientists detect gravitational waves from a new kind of nova, sparking a new era in astronomy

    New York Times – LIGO Detects Fierce Collision of Neutron Stars for the First Time

    Science – Merging neutron stars generate gravitational waves and a celestial light show

    CBS News – Gravitational waves – and light – seen in neutron star collision

    CBC News – Astronomers see source of gravitational waves for 1st time

    San Jose Mercury News – A bright light seen across the universe, proving Einstein right

    Popular Science – Gravitational waves just showed us something even cooler than black holes

    Scientific American – Gravitational Wave Astronomers Hit Mother Lode

    Nature – Colliding stars spark rush to solve cosmic mysteries

    National Geographic – In a First, Gravitational Waves Linked to Neutron Star Crash

    Associated Press – Astronomers witness huge cosmic crash, find origins of gold

    Science News – Neutron star collision showers the universe with a wealth of discoveries

    UCSC press release
    First observations of merging neutron stars mark a new era in astronomy


    Writing: Tim Stephens
    Video: Nick Gonzales
    Photos: Carolyn Lagattuta
    Header image: Illustration by Robin Dienel courtesy of the Carnegie Institution for Science
    Design and development: Rob Knight
    Project managers: Sherry Main, Scott Hernandez-Jason, Tim Stephens

    Dark Energy Survey

    Dark Energy Camera [DECam], built at FNAL

    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

    Noted in the video but not in the article:

    NASA/Chandra Telescope

    NASA/SWIFT Telescope

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

    CTIO PROMPT telescope telescope built by the University of North Carolina at Chapel Hill at Cerro Tololo Inter-American Observatory in Chilein the Chilean Andes.

    PROMPT The six domes at CTIO in Chile.

    NASA NuSTAR X-ray telescope

    See the full article here .

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    UCO Lick Shane Telescope
    UCO Lick Shane Telescope interior
    Shane Telescope at UCO Lick Observatory, UCSC

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    UC Santa Cruz campus
    The University of California, Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

    UCSC is the home base for the Lick Observatory.

    Lick Observatory's Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building
    Lick Observatory’s Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building

    Search for extraterrestrial intelligence expands at Lick Observatory
    New instrument scans the sky for pulses of infrared light
    March 23, 2015
    By Hilary Lebow
    The NIROSETI instrument saw first light on the Nickel 1-meter Telescope at Lick Observatory on March 15, 2015. (Photo by Laurie Hatch) UCSC Lick Nickel telescope

    Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

    “Infrared light would be an excellent means of interstellar communication,” said Shelley Wright, an assistant professor of physics at UC San Diego who led the development of the new instrument while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.

    Wright worked on an earlier SETI project at Lick Observatory as a UC Santa Cruz undergraduate, when she built an optical instrument designed by UC Berkeley researchers. The infrared project takes advantage of new technology not available for that first optical search.

    Infrared light would be a good way for extraterrestrials to get our attention here on Earth, since pulses from a powerful infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from great distances. It also takes less energy to send information using infrared signals than with visible light.

    UCSC alumna Shelley Wright, now an assistant professor of physics at UC San Diego, discusses the dichroic filter of the NIROSETI instrument. (Photo by Laurie Hatch)

    Frank Drake, professor emeritus of astronomy and astrophysics at UC Santa Cruz and director emeritus of the SETI Institute, said there are several additional advantages to a search in the infrared realm.

    “The signals are so strong that we only need a small telescope to receive them. Smaller telescopes can offer more observational time, and that is good because we need to search many stars for a chance of success,” said Drake.

    The only downside is that extraterrestrials would need to be transmitting their signals in our direction, Drake said, though he sees this as a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”

    Scientists have searched the skies for radio signals for more than 50 years and expanded their search into the optical realm more than a decade ago. The idea of searching in the infrared is not a new one, but instruments capable of capturing pulses of infrared light only recently became available.

    “We had to wait,” Wright said. “I spent eight years waiting and watching as new technology emerged.”

    Now that technology has caught up, the search will extend to stars thousands of light years away, rather than just hundreds. NIROSETI, or Near-Infrared Optical Search for Extraterrestrial Intelligence, could also uncover new information about the physical universe.

    “This is the first time Earthlings have looked at the universe at infrared wavelengths with nanosecond time scales,” said Dan Werthimer, UC Berkeley SETI Project Director. “The instrument could discover new astrophysical phenomena, or perhaps answer the question of whether we are alone.”

    NIROSETI will also gather more information than previous optical detectors by recording levels of light over time so that patterns can be analyzed for potential signs of other civilizations.

    “Searching for intelligent life in the universe is both thrilling and somewhat unorthodox,” said Claire Max, director of UC Observatories and professor of astronomy and astrophysics at UC Santa Cruz. “Lick Observatory has already been the site of several previous SETI searches, so this is a very exciting addition to the current research taking place.”

    NIROSETI will be fully operational by early summer and will scan the skies several times a week on the Nickel 1-meter telescope at Lick Observatory, located on Mt. Hamilton east of San Jose.

    The NIROSETI team also includes Geoffrey Marcy and Andrew Siemion from UC Berkeley; Patrick Dorval, a Dunlap undergraduate, and Elliot Meyer, a Dunlap graduate student; and Richard Treffers of Starman Systems. Funding for the project comes from the generous support of Bill and Susan Bloomfield.

    UCSC is the home base for the Lick Observatory.

    When two black holes or neutron stars collide, the event is so massive and disruptive that it sends gravitational waves rippling out across the fabric of space-time.

    Although predicted by Einstein’s theory of general relativity in 1915, it wasn’t until 100 years later that we were able to develop instrumentation sensitive enough to detect these ripples.

    The technology is still in its infancy and is being refined over time. This means, potentially, that there is a lot we still can’t detect.

    Every year, the researchers say, there are over 100,000 gravitational wave events that are too faint for the interferometers of the LIGO-Virgo collaboration to detect unambiguously.

    These are caused by smaller black hole collisions, and collisions much farther away. Rather than showing up as individual signal spikes, their signals resolve into a sort of “hum”.

    Researchers have been trying to find this hum for years – and now Thrane, Smith and their team believe they may have developed a method sensitive enough to detect it among the gravitational wave background static picked up by the interferometers.

    “Measuring the gravitational-wave background will allow us to study populations of black holes at vast distances,” Thrane said.

    “Someday, the technique may enable us to see gravitational waves from the Big Bang, hidden behind gravitational waves from black holes and neutron stars.”

    The team has developed an algorithm that can comb through the LIGO-Virgo static data and pick out the signals of the black hole collisions – when converted to audio, it’s an upsweep of sound that ends in a sort of loud “BLOOP.”

    “It’s the same thing your brain does when your car radio goes out of reception and goes to static,” Smith told the Sydney Morning Herald.

    “Little bits and pieces of radio stations still come through – but your brain is able to put them together and work out what song is playing.”

    To test it, they created simulations of black hole collisions, then had their algorithm try to pick them out of background static.

    They found that it wasn’t fooled by artefacts such as background glitches, and was reliably able to pick out unpredictable signals.

    It has yet to be applied to real data, but the researchers are confident it will work, especially run on a powerful new supercomputer at Swinburne University.

    OzSTAR, with a peak performance of 1.2 petaflops, will be used to sort through the vast amounts of data being generated by gravitational wave detectors, looking for black hole and neutron star mergers in real-time.

    “It gives us a taste of the universe at its most extreme,” Matthew Bailes, director of OzGrav, told the ABC.

    “It’s when you’ve sort of set the laws of physics to ‘stun’, and to a physicist that is an exciting place to probe.”

    The team’s research has been accepted into the journal Physical Review X.

    See the full article here .

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    Monash U campus

    Monash University (/ˈmɒnæʃ/) is an Australian public research university based in Melbourne, Australia. Founded in 1958, it is the second oldest university in the State of Victoria. Monash is a member of Australia’s Group of Eight and the ASAIHL, and is the only Australian member of the influential M8 Alliance of Academic Health Centers, Universities and National Academies. Monash is one of two Australian universities to be ranked in the The École des Mines de Paris (Mines ParisTech) ranking on the basis of the number of alumni listed among CEOs in the 500 largest worldwide companies.[6] Monash is in the top 20% in teaching, top 10% in international outlook, top 20% in industry income and top 10% in research in the world in 2016.[7]

    Monash enrolls approximately 47,000 undergraduate and 20,000 graduate students,[8] It also has more applicants than any university in the state of Victoria.

    Monash is home to major research facilities, including the Australian Synchrotron, the Monash Science Technology Research and Innovation Precinct (STRIP), the Australian Stem Cell Centre, 100 research centres[9] and 17 co-operative research centres. In 2011, its total revenue was over $2.1 billion, with external research income around $282 million.[10]

    The university has a number of centres, five of which are in Victoria (Clayton, Caulfield, Berwick, Peninsula, and Parkville), one in Malaysia.[11] Monash also has a research and teaching centre in Prato, Italy,[12] a graduate research school in Mumbai, India[13] and a graduate school in Jiangsu Province, China.[14] Since December 2011, Monash has had a global alliance with the University of Warwick in the United Kingdom.[15] Monash University courses are also delivered at other locations, including South Africa.

    The Clayton campus contains the Robert Blackwood Hall, named after the university’s founding Chancellor Sir Robert Blackwood and designed by Sir Roy Grounds.[16]

    In 2014, the University ceded its Gippsland campus to Federation University.[17] On 7 March 2016, Monash announced that it would be closing the Berwick campus by 2018.

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