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  • richardmitnick 11:26 am on April 26, 2019 Permalink | Reply
    Tags: , , , , , , , IPTA-International Pulsar Timing Array, , Neutron star mergers, ,   

    From University of Maryland CMNS: “The Past, Present and Future of Gravitational Wave Astronomy” 

    U Maryland bloc

    From University of Maryland


    CMNS

    Matthew Wright
    301-405-9267
    mewright@umd.edu

    UMD Astronomy Professor Coleman Miller co-authored wide-ranging review article for 150th anniversary of the journal Nature.

    1
    Coleman Miller, University of Maryland Astronomy Professor and Co-Director of the Joint Space-Science Institute. Miller co-authored a new review of the past, present, and future of gravitational wave astronomy for the journal Nature. Image credit: Coleman Miller.

    When Albert Einstein published his general theory of relativity in 1915, he gave the scientific community a wealth of theoretical predictions about the nature of space, time, matter and gravity. Unlike much of his prior work, however, general relativity wasn’t easily testable with experiments and direct observation.

    That all changed a century later, on September 14, 2015, when the twin Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors registered gravitational waves from the merger of two black holes.

    For the first time, the scientific community had definitive support for one of the greatest predictions arising from Einstein’s general theory of relativity—that the acceleration of massive objects can produce ripples in the fabric of spacetime.

    In just three short years since that initial observation, LIGO has made or contributed to a landslide of new discoveries, helping to usher in the age of gravitational wave astronomy. University of Maryland Astronomy Professor Coleman Miller, an expert in the theory and modeling of gravity, co-authored a review of the past, present, and future of gravitational wave astronomy for the journal Nature, published on April 25, 2019. The article is part of a series that celebrates the 150th anniversary of the journal, which was first published on November 4, 1869.

    “Direct observation of gravitational waves was an important test of general relativity that gave us access to information we simply didn’t have before,” said Miller, who is also a co-director of the Joint Space-Science Institute (JSI), a partnership between UMD and NASA’s Goddard Space Flight Center. “There is a very limited set of ways we can get information about the distant universe beyond our solar system. We were missing a lot of non-trivial events before we could detect gravitational waves. To offer some perspective: the final plunge of a black hole merger emits tens of times more energy in gravitational waves than all the stars in the visible universe radiate within the same period of time.”

    Miller is a co-author of more than 20 publications related to gravitational radiation. Although he served as the chair of the LIGO Program Advisory Committee for four years (2010-2014), Miller has not been directly involved in LIGO’s science operations. This provides him with a uniquely knowledgeable, yet scientifically objective, viewpoint on the topic.

    Co-authored with Nicolás Yunes of Montana State University, the review article traces the early history of attempts to investigate general relativity, including several indirect observations and theoretical work. Then, Miller and Yunes describe the contributions of UMD Physics Professor Joseph Weber (1919-2000), who was the first to suggest that it was physically possible to detect and measure gravitational waves.

    Beginning in the 1960s, Weber designed, built and operated a pair of solid aluminum bars—one near UMD’s campus and another just outside Chicago—which he suggested would resonate like a bell when struck by passing gravitational waves. Thus began a decades-long scientific quest that would involve hundreds of scientists the world over, including many UMD faculty and staff members and alumni. The physics community eventually settled on a completely different interferometer design that would become the basis for LIGO’s twin detector facilities in Livingston, Louisiana, and Hanford, Washington.

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    The collision of two black holes—a tremendously powerful event detected for the first time ever by the Laser Interferometer Gravitational-Wave Observatory, or LIGO on September 14, 2015—is seen in this still from a computer simulation. LIGO detected gravitational waves, or ripples in space and time generated as the black holes spiraled in toward each other, collided, and merged. This simulation shows how the merger would appear to human eyes. It was created by solving equations from Albert Einstein’s general theory of relativity using the LIGO data. Illustration: SXS.

    With the help of UMD Physics Professor and JSI Fellow Peter Shawhan and UMD College Park Professor of Physics Alessandra Buonanno—both principal investigators with the LIGO Scientific Collaboration—the construction and fine-tuning of the detectors resulted in LIGO’s historic first observation in 2015. Just two years later, in 2017, LIGO project leads Rainer Weiss of the Massachusetts Institute of Technology and Kip Thorne and Barry Barish of Caltech were recognized with the Nobel Prize in physics for the groundbreaking observation.

    LIGO followed the initial 2015 detection with several more observations of black hole mergers. But another major turning point came on August 17, 2017, when scientists across the world made the first direct observation of a merger between two neutron stars—the dense, collapsed cores that remain after large stars die in a supernova. The merger was the first cosmological event observed in both gravitational waves and—with the help of a large array of ground- and space-based telescopes—the entire spectrum of light, from gamma rays to radio waves.

    “This event gave us instant confirmation that gravitational waves travel at a speed that is indistinguishable from the speed of light,” Miller explained. “For years, there have been alternate theories of gravity that would explain what dark matter is thought to do. But many of these relied on gravitational waves reacting to the gravity of massive objects differently than light does. This was not found to be the case in the wake of a neutron star merger, so observing this event eliminated a wide swath of these theories immediately.”

    The neutron star merger also yielded the first direct observation of a kilonova—a massive explosion now believed to create most of the heavy elements in the universe. Led by UMD’s Eleonora Troja, an associate research scientist in the Department of Astronomy, an early analysis of the kilonova suggested that the explosion produced a staggering amount of platinum and gold, with a combined mass several hundred times that of Earth.

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    This iconc illustration depicts the merger of two neutron stars. The rippling spacetime grid represents gravitational waves that travel out from the collision, while the narrow beams show the burst of gamma rays launched just seconds after the gravitational waves. Swirling clouds of material ejected from the merging stars glow with visible and other wavelengths of light. Image credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet

    This finding alone strongly swung the needle toward a conclusion that all elements heavier than iron are all produced in neutron star mergers,” Miller explained. “That’s very exciting.”

    On April 1, 2019, LIGO began its third observing run, after a series of upgrades to its lasers, mirrors and other components. While Miller is hesitant to set his own expectations too high, he is hopeful that the latest round will yield some new surprises.

    “The universe will give us what it will give us. That said, it would be wonderful to see a merger between a black hole and a neutron star,” Miller said. “And a few extra double neutron star mergers certainly wouldn’t hurt.”

    Looking further down the line, Miller and Yunes also assessed the prospects for observing the gravitational wave background. This ever-present hum of gravitational waves is thought to contain the fingerprints of orbiting black holes, neutron stars and other massive objects. These pairs of objects may be tens, hundreds or even thousands of years away from merging—and thus are unable to produce a spike in gravitational waves detectable with current technology. Miller likens the effort to adjusting one’s ears to the din of conversation in a crowded room.

    “Imagine arriving at a party. At first, you can see that everyone is talking, but the sound registers quietly, if at all,” Miller said. “Then your hearing gets better. You’re not yet able to hear every individual, but you can hear the sum total. Then, as your hearing gets better, you can hear some nearby conversations and can distinguish between people who are near and far.”

    Within the next few years, the International Pulsar Timing Array (IPTA) collaboration could become the first to detect the subtle drone from thousands of pairs of supermassive black holes.

    4

    With the help of the world’s largest radio telescopes, IPTA will carefully track deviations in the precise, clock-like flashing of roughly 100 small, rotating neutron stars called millisecond pulsars. These deviations will help IPTA detect gravitational fluctuations from orbiting pairs of supermassive black holes, each of which contains billions of times the mass of the sun.

    The next big step in gravitational wave astronomy will be the launch of the Laser Interferometer Space Antenna (LISA) mission, led by the European Space Agency in partnership with NASA.


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

    This trio of satellites, currently slated for deployment by 2034, will be sensitive to a lower range of gravitational wave frequencies than LIGO. As such, LISA should be able to observe events that LIGO cannot detect, such as mergers that involve one or more supermassive black holes.

    “A lot can happen in 15 years. In the meantime, I plan to eat my vegetables so I can be around to appreciate LISA’s findings when the satellites are launched,” Miller said. “The excitement in the astrophysical community is only increasing. Expectation of new discovery has been one the enduring excitements of gravitational wave astronomy.”

    See the full article here .

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    About CMNS

    The thirst for new knowledge is a fundamental and defining characteristic of humankind. It is also at the heart of scientific endeavor and discovery. As we seek to understand our world, across a host of complexly interconnected phenomena and over scales of time and distance that were virtually inaccessible to us a generation ago, our discoveries shape that world. At the forefront of many of these discoveries is the College of Computer, Mathematical, and Natural Sciences (CMNS).

    CMNS is home to 12 major research institutes and centers and to 10 academic departments: astronomy, atmospheric and oceanic science, biology, cell biology and molecular genetics, chemistry and biochemistry, computer science, entomology, geology, mathematics, and physics.

    Our Faculty

    Our faculty are at the cutting edge over the full range of these disciplines. Our physicists fill in major gaps in our fundamental understanding of matter, participating in the recent Higgs boson discovery, and demonstrating the first-ever teleportation of information between atoms. Our astronomers probe the origin of the universe with one of the world’s premier radio observatories, and have just discovered water on the moon. Our computer scientists are developing the principles for guaranteed security and privacy in information systems.

    Our Research

    Driven by the pursuit of excellence, the University of Maryland has enjoyed a remarkable rise in accomplishment and reputation over the past two decades. By any measure, Maryland is now one of the nation’s preeminent public research universities and on a path to become one of the world’s best. To fulfill this promise, we must capitalize on our momentum, fully exploit our competitive advantages, and pursue ambitious goals with great discipline and entrepreneurial spirit. This promise is within reach. This strategic plan is our working agenda.

    The plan is comprehensive, bold, and action oriented. It sets forth a vision of the University as an institution unmatched in its capacity to attract talent, address the most important issues of our time, and produce the leaders of tomorrow. The plan will guide the investment of our human and material resources as we strengthen our undergraduate and graduate programs and expand research, outreach and partnerships, become a truly international center, and enhance our surrounding community.

    Our success will benefit Maryland in the near and long term, strengthen the State’s competitive capacity in a challenging and changing environment and enrich the economic, social and cultural life of the region. We will be a catalyst for progress, the State’s most valuable asset, and an indispensable contributor to the nation’s well-being. Achieving the goals of Transforming Maryland requires broad-based and sustained support from our extended community. We ask our stakeholders to join with us to make the University an institution of world-class quality with world-wide reach and unparalleled impact as it serves the people and the state of Maryland.

    Our researchers are also at the cusp of the new biology for the 21st century, with bioscience emerging as a key area in almost all CMNS disciplines. Entomologists are learning how climate change affects the behavior of insects, and earth science faculty are coupling physical and biosphere data to predict that change. Geochemists are discovering how our planet evolved to support life, and biologists and entomologists are discovering how evolutionary processes have operated in living organisms. Our biologists have learned how human generated sound affects aquatic organisms, and cell biologists and computer scientists use advanced genomics to study disease and host-pathogen interactions. Our mathematicians are modeling the spread of AIDS, while our astronomers are searching for habitable exoplanets.

    Our Education

    CMNS is also a national resource for educating and training the next generation of leaders. Many of our major programs are ranked among the top 10 of public research universities in the nation. CMNS offers every student a high-quality, innovative and cross-disciplinary educational experience that is also affordable. Strongly committed to making science and mathematics studies available to all, CMNS actively encourages and supports the recruitment and retention of women and minorities.

    Our Students

    Our students have the unique opportunity to work closely with first-class faculty in state-of-the-art labs both on and off campus, conducting real-world, high-impact research on some of the most exciting problems of modern science. 87% of our undergraduates conduct research and/or hold internships while earning their bachelor’s degree. CMNS degrees command respect around the world, and open doors to a wide variety of rewarding career options. Many students continue on to graduate school; others find challenging positions in high-tech industry or federal laboratories, and some join professions such as medicine, teaching, and law.

     
  • richardmitnick 1:26 pm on August 26, 2017 Permalink | Reply
    Tags: , , , , , , , Neutron star mergers, Rumours swell over new kind of gravitational-wave sighting,   

    From Nature: “Rumours swell over new kind of gravitational-wave sighting” 

    Nature Mag
    Nature

    24 August 2017
    Davide Castelvecchi

    Gossip over potential detection of colliding neutron stars has astronomers in a tizzy.

    1
    The galaxy NGC 4993 (fuzzy bright spot) in the constellation Hydra, where detectors are rumoured to have spotted gravitational waves from a neutron star merger. Digitized Sky Survey

    Astrophysicists may have detected gravitational waves last week from the collision of two neutron stars in a distant galaxy — and telescopes trained on the same region might also have spotted the event.

    Rumours to that effect are spreading fast online, much to researchers’ excitement. Such a detection could mark a new era of astronomy: one in which phenomena are both seen by conventional telescopes and ‘heard’ as vibrations in the fabric of space-time. “It would be an incredible advance in our understanding,” says Stuart Shapiro, an astrophysicist at the University of Illinois at Urbana–Champaign.

    Scientists who work with gravitational-wave detectors won’t comment on the gossip because the data is still under analysis. Public records show that telescopes around the world have been looking at the same galaxy since last week, but astronomers caution that they could have been picking up signals from an unrelated source.

    As researchers hunt for signals in their data, Nature explains what is known so far, and the possible implications of any discovery.

    What is the gossip?

    The Laser Interferometer Gravitational-Wave Observatory (LIGO) in Louisiana and Washington state has three times detected gravitational waves — ripples in the fabric of space-time — emerging from colliding black holes.


    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

    But scientists have been hoping to detect ripples from another cosmic cataclysm, such as the merger of neutron stars, remnants of large stars that exploded but were not massive enough to collapse into a black hole. Such an event should also emit radiation across the electromagnetic spectrum — from radio waves to γ-rays — which telescopes might be able to pick up.

    On 18 August, astronomer J. Craig Wheeler of the University of Texas at Austin began the public rumour mill when he tweeted, “New LIGO. Source with optical counterpart. Blow your sox off!” An hour later, astronomer Peter Yoachim of the University of Washington in Seattle tweeted that LIGO had seen a signal with an optical counterpart (that is, something that telescopes could see) from a galaxy called NGC 4993, which is around 40 million parsecs (130 million light years) away in the southern constellation Hydra. “Merging neutron-neutron star is the initial call”, he followed up. Some astronomers who do not want to be identified say that rumours had been privately circulating before Wheeler’s and Yoachim’s tweets.

    If gravitational-wave researchers saw a signal, it is plausible that they could know very quickly whether it emerged from colliding black holes or neutron stars, because each type of event has its own signature, even though data must be studied carefully to be more precise about an event’s origin.

    It’s also possible that LIGO’s sister observatory Virgo in Pisa, Italy, which has been helping LIGO to hunt for gravitational waves since August, after taking a break for an upgrade, might have spotted the event.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    That would give researchers more confidence about its source. (Virgo has an average sensitivity for neutron-star mergers of only 25 million to 27 million parsecs, but in some regions of the sky, it can see farther, up to 60 million parsecs away, says physicist Giovanni Losurdo, who led the detector’s upgrade work.)

    Both Wheeler and Yoachim declined to comment, and Wheeler later apologized on Twitter. “Right or wrong, I should not have sent that tweet. LIGO deserves to announce when they deem appropriate. Mea culpa,” he wrote.

    What about the telescope observations?

    Public records show that NASA’s Fermi Gamma-ray Space Telescope has spotted γ-rays emerging from the same region of sky as the potential gravitational-wave source.

    NASA/Fermi Telescope

    A senior Fermi member declined to comment on the observation, but it would be consistent with expectations that neutron-star collisions may be behind the enigmatic phenomena known as short γ-ray bursts (GRBs), which typically last a couple of seconds and are usually followed by an afterglow of visible light and sometimes, radio waves and x-rays, lasting up to a few days.

    But although the Fermi telescope has seen a GRB, it may not be able to pinpoint its origin with high precision, astronomers caution.

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    A simulation of the merger of a binary neutron star: magnetic field lines are in white. Simulations by M. Ruiz, R. N. Lang, V. Paschalidis and S. L.Shapiro at the University of Illinois at Urbana-Champaign, with visualization assistance from the Illinois Relativity REU team.

    Other telescopes were also turned to look at NGC 4993 after an alert about a potential gravitational wave sighting. On 22 August, a Twitter feed called Space Telescope Live, which provides live updates of what the Hubble Space Telescope is looking at, suggested that a team of astronomers was looking at a binary neutron-star merger using the probe’s on-board spectrograph, which is what astronomers would normally use to look at the afterglow of a short GRB. The Hubble tweet has since been deleted. Public records also confirm that multiple teams have used the Hubble Space Telescope over the last week to examine NGC 4993, and state as their reason that they are trying to follow up on a candidate observation of gravitational waves.

    On 23 August, a commenter on the blog of astrophysicist Peter Coles, of Cardiff University in the UK, noted that NASA’s Chandra X-ray observatory had jumped into the action, too.

    The Chandra website contains a public record of an observation made on 19 August.

    NASA/Chandra Telescope

    The telescope pointed at celestial coordinates in the galaxy NGC 4993 and observed an event called SGRB170817A — indicating ‘short GRB of 2017-August-17’. The most revealing part of the report is the “trigger criteria” section, which explains the reason for over-riding any previously scheduled observation to turn the telescope in that direction. It says: “Gravitational wave source detected by aLIGO, VIRGO, or both.”

    Publicly available records from other major astronomy facilities — including the European Southern Observatory’s Very Large Telescope and the world’s premiere radio observatory, the Atacama Large Millimeter/submillimeter Array (ALMA), both in Chile — show that those also targeted NGC 4993 on 18 and 19 August.

    ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    What could we learn from a neutron-star merger?

    Gravitational-wave signals from black-hole mergers are brief, typically lasting a second or less. But a neutron-star merger could yield a signal that lasts up to a minute: neutron stars are less massive than black holes and emit less-powerful gravitational waves, so it takes longer for their orbits to decay and for the stars to spiral into each other. Longer events enable much more precise tests of Albert Einstein’s general theory of relativity, which predicts gravitational waves — perhaps giving more clues to the origins of neutron stars.

    The short GRB that telescopes might have observed would be significant, too — not least because if it is associated with gravitational waves, it would validate decades of astrophysical theorizing that GRBs are associated with neutron-star collisions. “Only gravitational waves could give us the smoking gun,” says Eleonora Troja, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

    Still, a short GRB would be an important discovery on its own. Most such events are seen in the distant Universe, billions of parsecs away. NGC 4993, at 40 million parsecs away, would probably be the closest short GRB ever detected, says astrophysicist Derek Fox of Pennsylvania State University in University Park.

    Details of the gravitational waves at the time of the collision and in the following instances could also reveal information about the structure of neutron stars — which is largely unknown — and whether their merger resulted again in a neutron star or in the formation of a new black hole.

    When will we know?

    On 25 August, LIGO and Virgo will end their current data-collecting run. After that, researchers will post only a “top-level update”, meaning a brief note indicating whether the observatories have picked up potential ‘candidate events’ that need further analysis, says David Shoemaker, a physicist at the Massachusetts Institute of Technology who is LIGO’s spokesperson.

    “It will take time to do justice to the data, and ensure that we publish things in which we have very high confidence,” he says.

    Update 25 August: The LIGO–Virgo collaboration posted its top-level update, saying: “Some promising gravitational-wave candidates have been identified in data from both LIGO and Virgo during our preliminary analysis, and we have shared what we currently know with astronomical observing partners. We are working hard to assure that the candidates are valid gravitational-wave events, and it will require time to establish the level of confidence needed to bring any results to the scientific community and the greater public. We will let you know as soon we have information ready to share.”

    See the full article here .

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

     
    • Jose 5:40 am on October 29, 2017 Permalink | Reply

      The detection of the gravitational waves produced by the merger of two neutron stars –GW170817– has allowed scientists to fix at 70 km/s per megaparsec * the value of the increase in speed of the expansion of the universe in the 130 million light years that separate us from the origin of said merger.
      As these calculations approach the speed of light throughout the age of the universe, we can do the inverse calculation to determine the average increase in the velocity of expansion so that the observable universe is of the age stated by the Big Bang Theory.
      The result is 300.000 km/s /(13.799/3,26) Mpc =70,820 km/s Mpc. https://molwick.com/en/gravitation/072-gravitational-waves.html#big-bang

      Like

    • richardmitnick 7:09 am on October 29, 2017 Permalink | Reply

      Thanks for visiting sciencesprings. I went to your site. Beautiful and instructive.

      Like

    • Jose 12:34 pm on October 29, 2017 Permalink | Reply

      Thank you too. My pleasure!

      Like

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