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  • richardmitnick 9:49 am on May 8, 2019 Permalink | Reply
    Tags: , , , , Caltech/MIT Advanced aLigo, , , , , , Persistent gravitational wave observables, , When two massive objects such as neutron stars or black holes collide they send shockwaves through the Universe rippling the very fabric of space-time itself.   

    From Cornell University via Science Alert: “Gravitational Waves Could Be Leaving Some Weird Lasting Effects in Their Wake” 


    From Cornell University

    via

    ScienceAlert

    Science Alert

    8 MAY 2019
    MICHELLE STARR

    1
    (Henze/NASA)

    The faint, flickering distortions of space-time we call gravitational waves are tricky to detect, and we’ve only managed to do so in recent years. But now scientists have calculated that these waves may leave more persistent traces of their passing – traces we may also be able to detect.

    Such traces are called ‘persistent gravitational wave observables’, and in a new paper [Physical Review D], an international team of researchers [see paper for science team authors] has refined the mathematical framework for defining them. In the process, they give three examples of what these observables could be.

    Here’s the quick lowdown on gravitational waves: When two massive objects such as neutron stars or black holes collide, they send shockwaves through the Universe, rippling the very fabric of space-time itself. This effect was predicted by Einstein in his theory of general relativity in 1916, but it wasn’t until 2015 that we finally had equipment sensitive enough to detect the ripples.

    That equipment is an interferometer that shoots two or more laser beams down arms that are several kilometres in length. The wavelengths of these laser beams interfere to cancel each other out, so, normally, no light hits the instrument’s photodetectors.


    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)

    But when a gravitational wave hits, the warping of space-time causes these laser beams to oscillate, shrinking and stretching. This means that their interference pattern is disrupted, and they no longer cancel each other out – so the laser hits the photodetector. The pattern of the light that hits can tell scientists about the event that created the wave.

    But that shrinking and stretching and warping of space-time, according to astrophysicist Éanna Flanagan of Cornell University and colleagues, could be having a much longer-lasting effect.

    As the ripples in space-time propagate, they can change the velocity, acceleration, trajectories and relative positions of objects and particles in their way – and these features don’t immediately return to normal afterwards, making them potentially observable.

    Particles, for instance, disturbed by a burst of gravitational waves, could show changes. In their new framework, the research team mathematically detailed changes that could occur in the rotation rate of a spinning particle, as well as its acceleration and velocity.

    Another of these persistent gravitational wave observables involves a similar effect to time dilation, whereby a strong gravitational field slows time.

    Because gravitational waves warp both space and time, two extremely precise and synchronised clocks in different locations, such as atomic clocks, could be affected by gravitational waves, showing different times after the waves have passed.

    Finally, the gravitational waves could actually permanently shift the relative positions in the mirrors of a gravitational wave interferometer – not by much, but enough to be detectable.

    Between its first detection in 2015 and last year, the LIGO-Virgo gravitational wave collaboration detected a handful of events before LIGO was taken offline for upgrades.

    At the moment, there are not enough detections in the bank for a meaningful statistical database to test these observables.

    But LIGO-Virgo was switched back on on 1 April, and since then has been detecting at least one gravitational wave event per week.

    The field of gravitational wave astronomy is heating up, space scientists are itching to test new mathematical calculations and frameworks, and it won’t be long before we’re positively swimming in data.

    This is just such an incredibly exciting time for space science, it really is.

    See the full article here .

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    Once called “the first American university” by educational historian Frederick Rudolph, Cornell University represents a distinctive mix of eminent scholarship and democratic ideals. Adding practical subjects to the classics and admitting qualified students regardless of nationality, race, social circumstance, gender, or religion was quite a departure when Cornell was founded in 1865.

    Today’s Cornell reflects this heritage of egalitarian excellence. It is home to the nation’s first colleges devoted to hotel administration, industrial and labor relations, and veterinary medicine. Both a private university and the land-grant institution of New York State, Cornell University is the most educationally diverse member of the Ivy League.

    On the Ithaca campus alone nearly 20,000 students representing every state and 120 countries choose from among 4,000 courses in 11 undergraduate, graduate, and professional schools. Many undergraduates participate in a wide range of interdisciplinary programs, play meaningful roles in original research, and study in Cornell programs in Washington, New York City, and the world over.

     
  • richardmitnick 3:07 pm on May 6, 2019 Permalink | Reply
    Tags: "LIGO and Virgo Detect Neutron Star Smash-Ups", , Caltech/MIT Advanced aLigo, Gravitatonal wave astronomy,   

    From MIT Caltech Advanced aLIGO: “LIGO and Virgo Detect Neutron Star Smash-Ups” 

    MIT Caltech Caltech Advanced aLigo new bloc

    From MIT Caltech Advanced aLIGO

    May 2, 2019

    On April 25, 2019, the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European-based Virgo detector registered gravitational waves from what appears likely to be a crash between two neutron stars—the dense remnants of massive stars that previously exploded. One day later, on April 26, the LIGO-Virgo network spotted another candidate source with a potentially interesting twist: it may in fact have resulted from the collision of a neutron star and black hole, an event never before witnessed.

    “The universe is keeping us on our toes,” says Patrick Brady, spokesperson for the LIGO Scientific Collaboration and a professor of physics at the University of Wisconsin-Milwaukee. “We’re especially curious about the April 26 candidate. Unfortunately, the signal is rather weak. It’s like listening to somebody whisper a word in a busy café; it can be difficult to make out the word or even to be sure that the person whispered at all. It will take some time to reach a conclusion about this candidate.”

    “NSF’s LIGO, in collaboration with Virgo, has opened up the universe to future generations of scientists,” says NSF Director France Córdova. “Once again, we have witnessed the remarkable phenomenon of a neutron star merger, followed up closely by another possible merger of collapsed stars. With these new discoveries, we see the LIGO-Virgo collaborations realizing their potential of regularly producing discoveries that were once impossible. The data from these discoveries, and others sure to follow, will help the scientific community revolutionize our understanding of the invisible universe.”

    The discoveries come just weeks after LIGO and Virgo turned back on. The twin detectors of LIGO—one in Washington and one in Louisiana—along with Virgo, located at the European Gravitational Observatory (EGO) in Italy, resumed operations April 1, after undergoing a series of upgrades to increase their sensitivities to gravitational waves—ripples in space and time. Each detector now surveys larger volumes of the universe than before, searching for extreme events such as smash-ups between black holes and neutron stars.

    “Joining human forces and instruments across the LIGO and Virgo collaborations has been once again the recipe of an incomparable scientific month, and the current observing run will comprise 11 more months,” says Giovanni Prodi, the Virgo Data Analysis Coordinator, at the University of Trento and the Istituto Nazionale di Fisica Nucleare (INFN) in Italy. “The Virgo detector works with the highest stability, covering the sky 90 percent of the time with useful data. This is helping in pointing to the sources, both when the network is in full operation and at times when only one of the LIGO detectors is operating. We have a lot of groundbreaking research work ahead.”

    In addition to the two new candidates involving neutron stars, the LIGO-Virgo network has, in this latest run, spotted three likely black hole mergers. In total, since making history with the first-ever direct detection of gravitational waves in 2015, the network has spotted evidence for two neutron star mergers, 13 black hole mergers, and one possible black hole-neutron star merger.

    When two black holes collide, they warp the fabric of space and time, producing gravitational waves. When two neutron stars collide, they not only send out gravitational waves but also light. That means telescopes sensitive to light waves across the electromagnetic spectrum can witness these fiery impacts together with LIGO and Virgo. One such event occurred in August 2017: LIGO and Virgo initially spotted a neutron star merger in gravitational waves and then, in the days and months that followed, about 70 telescopes on the ground and in space witnessed the explosive aftermath in light waves, including everything from gamma rays to optical light to radio waves.

    In the case of the two recent neutron star candidates, telescopes around the world once again raced to track the sources and pick up the light expected to arise from these mergers. Hundreds of astronomers eagerly pointed telescopes at patches of sky suspected to house the signal sources. However, at this time, neither of the sources has been pinpointed.

    “The search for explosive counterparts of the gravitational-wave signal is challenging due to the amount of sky that must be covered and the rapid changes in brightness that are expected,” says Brady. “The rate of neutron star merger candidates being found with LIGO and Virgo will give more opportunities to search for the explosions over the next year.”

    The April 25 neutron star smash-up, dubbed S190425z, is estimated to have occurred about 500 million light-years away from Earth. Only one of the twin LIGO facilities picked up its signal along with Virgo (LIGO Livingston witnessed the event but LIGO Hanford was offline). Because only two of the three detectors registered the signal, estimates of the location in the sky from which it originated were not precise, leaving astronomers to survey nearly one-quarter of the sky for the source.

    The possible April 26 neutron star-black hole collision (referred to as S190426c) is estimated to have taken place roughly 1.2 billion light-years away. It was seen by all three LIGO-Virgo facilities, which helped better narrow its location to regions covering about 1,100 square degrees, or about 3 percent of the total sky.

    “The latest LIGO-Virgo observing run is proving to be the most exciting one so far,” says David H. Reitze of Caltech, Executive Director of LIGO. “We’re already seeing hints of the first observation of a black hole swallowing a neutron star. If it holds up, this would be a trifecta for LIGO and Virgo—in three years, we’ll have observed every type of black hole and neutron star collision. But we’ve learned that claims of detections require a tremendous amount of painstaking work—checking and rechecking—so we’ll have to see where the data takes us.”

    The Collaborations

    LIGO is funded by NSF and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects.

    Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project.

    More than 1,200 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. A list of additional partners is available at https://my.ligo.org/census.php.

    The Virgo collaboration consists of more than 300 physicists and engineers belonging to 28 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; 11 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with IFAE and the Universities of Valencia and Barcelona; two in Belgium with the Universities of Liege and Louvain; Jena University in Germany; and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN, and Nikhef. A list of the Virgo Collaboration can be found at http://public.virgo-gw.eu/the-virgo-collaboration/. More information is available on the Virgo website at http://www.virgo-gw.eu.

    European Gravitational Observatory

    See the full article here .

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    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

    1
    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)

     
  • richardmitnick 9:49 am on May 4, 2019 Permalink | Reply
    Tags: , , , , Caltech/MIT Advanced aLigo, , , ,   

    From MIT News: “3 Questions: Salvatore Vitale on LIGO’s latest detections” 

    MIT News
    MIT Widget

    From MIT News

    May 2, 2019
    Jennifer Chu

    1
    Salvatore Vitale, assistant professor of physics at MIT and member of the LIGO Scientific Collaboration. Courtesy of MIT Kavli Institute for Astrophysics and Space Research.

    Kavli MIT Institute of Astrophysics and Space Research

    “We will keep listening for these faint and remote cosmic whispers,” says the physics professor.

    It’s been just three weeks since LIGO resumed its hunt for cosmic ripples through space-time, and already the gravitational-wave hunter is off to a running start.

    One of the detections researchers are now poring over is a binary neutron star merger — a collision of two incredibly dense stars, nearly 500 million light years away. The power of this stellar impact set off gravitational waves across the cosmos, eventually reaching Earth as infinitely small ripples that were picked up by LIGO (the Laser Interferometer Gravitational-wave Observatory, operated jointly by Caltech and MIT), as well as by Virgo, LIGO’s counterpart in Italy, on April 25 at 4 a.m. ET.



    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

    Researchers have determined that the source of the gravitational wave signal is likely a binary neutron star merger, which they’ve dubbed #S190425z. This is the second time that LIGO has discovered such a source.

    The other neutron star merger, detected in 2017, was also the first event captured by LIGO that was also observed using optical telescopes. As astronomers around the world pointed telescopes at this first neutron star merger, they were able to see the brilliant “kilonova” explosion generated as the two stars merged. They also detected signatures of gold and platinum in the aftermath — direct evidence for how heavy elements are produced in the universe.

    With LIGO’s new detection, astronomers are again pointing telescopes to the skies and searching for optical traces of the stellar merger and any resulting cosmic goldmine.

    MIT News caught up with Salvatore Vitale, assistant professor of physics at MIT and a member of the LIGO Scientific Collaboration, about this newest stellar discovery and hints of even more “cosmic whispers” on the horizon — including the tantalizing possibility that LIGO has also captured the collision of a black hole and a neutron star.

    Q: Walk us through the moment of discovery. When did this signal come in, and what told you that it was likely a binary neutron star merger?

    A: The signal hit Earth at 4:18 a.m. EDT. Unfortunately, at that time the LIGO detector in Hanford, Washington, was not collecting data. The signal was thus detected by the LIGO instrument in Baton Rouge, Louisiana, and the Virgo detector in Italy.

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

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Having only two detectors online did not affect our confidence of it being real, since neutron star binaries spend more than one minute in our detectors and these kinds of very long chirps cannot easily be confused with instrumental artifacts or other sources of noise. Similarly, we were able to measure extremely well the mass of the source, which told us it was a binary neutron star, the second ever detected by LIGO and Virgo.

    The main consequence of only having two detectors online was that it hurt our ability to localize the source in the sky. The sky map we sent out had a very large uncertainty, over 10,000 square degrees, which is a huge area to follow up, if you are looking for an electromagnetic counterpart.

    Q: Since the notice from LIGO went out, astronomers have been training telescopes on the sky. What have they been able to find about this new merger, and how is it different from the one LIGO detected in 2017?

    A: When two neutron stars smash one against the other, they trigger a cataclysmic explosion that releases huge amounts of energy and creates some of the heaviest elements in the universe (gold, among others). Finding both gravitational and electromagnetic waves can tell us about the environment in which these systems form, how they shine, their role in enriching galaxies with metals, and about the universe. This is why we routinely and automatically send public alerts to astronomers, so that they can try to identify the sources of our gravitational-wave events.

    This is challenging for S190425z, since it has been localized poorly (compare 10,000 square degrees for S190425z with 30 square degrees for the first binary neutron star merger, GW170817). Another important difference is that S190425z was nearly four times further away. Both these factors make it harder to successfully find an electromagnetic counterpart to S190425z. You want to scan a much larger area, and you want to find a weaker and more distant source. This doesn’t mean that astronomers are not trying hard! In fact, in the last 36 hours there have been dozens of observations. So far nothing too convincing, but a lot of excitement! It is nice to see the broader community so engaged with the follow-up of LIGO and Virgo’s events.

    Q: Since it started its newest observing run, LIGO has been detecting at least one gravitational wave source per week. What does this say about what sort of extreme phenomena are happening in the universe, on a daily basis?

    A: The last few weeks have been incredibly exciting! So far we are making discoveries at roughly the rate we were expecting: one binary black hole a week and one binary neutron star a month. This confirms our expectations that gravitational waves can really play a major role in understanding the most extreme objects of the universe.

    It also says that it is not uncommon that two stellar-mass black holes merge, which was not obvious at all before LIGO and Virgo discovered them. We still don’t know if the black holes pairs we are seeing had been together their whole cosmic life, first as normal stars, then as black holes, or if instead they were born separately and then just happened to meet and form a binary system. Both avenues are possible, and with a few more tens of detections we should be able to tell which of these two scenarios happens more often.

    Then there is always the possibility of detecting something new and unexpected! As I started drafting these answers, we detected #S190426c, which, if of astrophysical origin, could be the first neutron star colliding into a black hole ever detected by humans. We will know more in the next few weeks, and we will keep listening for these faint and remote cosmic whispers.

    See the full article here .


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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 8:12 am on May 3, 2019 Permalink | Reply
    Tags: "Have scientists observed a black hole swallowing a neutron star?", , , , Caltech/MIT Advanced aLigo, , , , ,   

    From Cardiff University: “Have scientists observed a black hole swallowing a neutron star?” 

    Cardiff University

    From Cardiff University

    3 May 2019

    Professor Mark Hannam
    Head of Gravitational Physics Group
    Director of the Gravity Exploration Institute

    1
    Now iconic image NSF/LIGO/Sonoma State University/A. Simonnet

    Within weeks of switching their machines back on to scour the sky for more sources of gravitational waves, scientists are poring over data in an attempt to further understand an unprecedented cosmic event.

    Astronomers working at the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European-based Virgo detector have reported the possible detection of gravitational waves emanating from the collision of a neutron star and a black hole.


    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)

    The signal, detected on 26 April, came just weeks after the teams turned the updated detectors back on to start their third observation run, named “O3”.

    “The universe is keeping us on our toes,” says Patrick Brady, spokesperson for the LIGO Scientific Collaboration and a professor of physics at the University of Wisconsin-Milwaukee. “We’re especially curious about the April 26 candidate. Unfortunately, the signal is rather weak. It’s like listening to somebody whisper a word in a busy café; it can be difficult to make out the word or even to be sure that the person whispered at all. It will take some time to reach a conclusion about this candidate.”

    The possible detection not only throws light on an event that up until now has never been observed, but also confirms the unprecedented accuracy with which the gravitational wave detectors are now operating.

    Included in the latest batch of discoveries is another possible merger between two neutron stars – potentially the second time this has been observed by the LIGO and Virgo teams – as well as a further three interesting black hole mergers.

    Professor Mark Hannam, a member of the LIGO team and Director of Cardiff University’s Gravity Exploration Institute said: “Yet again the LIGO and Virgo detectors have surpassed expectations. Our most optimistic estimates were for a detection every week, and the first month of the run gave us five candidates.”

    Dr Vivien Raymond, from Cardiff University’s Gravity Exploration Institute, said: “LIGO-Virgo’s third observing run has already proven to be more interesting than we expected, barely a month after it started. It’s exciting to think about the next surprises in the Universe for us to discover.”

    Gravitational waves are ripples in space produced by massive cosmic events such as the collision of black holes or the explosion of supernovae.

    Research undertaken by Cardiff University’s Gravity Exploration Institute has laid the foundations for how we go about detecting gravitational waves with the development of novel algorithms and software that have now become standard tools for detecting the elusive signals.

    The Institute also includes world-leading experts in the collision of black holes, who have produced large-scale computer simulations of what is to be expected and observed when these violent events occur, as well as experts in the design of gravitational-wave detectors.

    The twin detectors of LIGO—one in Washington and one in Louisiana—along with Virgo, located at the European Gravitational Observatory (EGO) in Italy, resumed operations on 1 April , after undergoing a series of upgrades to increase their sensitivities to gravitational waves—ripples in space and time.

    Each detector now surveys larger volumes of the universe than before, searching for extreme events such as smash-ups between black holes and neutron stars.

    In total, since making history with the first-ever direct detection of gravitational waves in 2015, the network has spotted evidence for two neutron star mergers; 13 black hole mergers; and one possible black hole-neutron star merger.

    See the full article here .


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    Please help promote STEM in your local schools.

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    Cardiff Unversity is an ambitious and innovative university with a bold and strategic vision located in a beautiful and thriving capital city. Our research is world-leading and we provide an educationally outstanding experience for our students.

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  • richardmitnick 2:02 pm on May 1, 2019 Permalink | Reply
    Tags: , , , Caltech/MIT Advanced aLigo, , , , , QRPN-quantum radiation pressure noise   

    From MIT News: “Quantum measurement could improve gravitational wave detection sensitivity” 

    MIT News
    MIT Widget

    From MIT News

    May 1, 2019
    Brittany Flaherty | School of Science

    Research could enable a new suite of experiments to measure quantum activity at room temperature.

    1
    New technology allows LIGO researchers to model noise from quantum phenomena at room temperature. The green path shows the optical fiber that carries light into the chamber, and the red path shows where the light exits.

    Minutes before dawn on Sept. 14, 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO) became the first-ever instrument on Earth to directly detect a gravitational wave. This work, led by the LIGO Scientific Collaboration with prominent roles from MIT and Caltech, was the first confirmation of this consequence of Albert Einstein’s theory of general relativity — 100 years after he first predicted it. The groundbreaking detection represented an enormous step forward in the field of astrophysics. In the years since, scientists have striven to achieve even greater sensitivity in the LIGO detectors.

    New research has taken investigators one step closer to this goal. Nergis Mavalvala, the Curtis and Kathleen Marble Professor of Astrophysics at MIT, postdoc Robert Lanza, graduate student Nancy Aggarwal, and their collaborators at Louisiana State University (LSU) recently conducted experiments that could help overcome a future limitation in Advanced LIGO. In their laboratory study, the team successfully measured a type of noise that will soon hold the LIGO instruments back from detecting gravitational waves with greater sensitivity.

    Their study, reported recently in Nature, was the first to measure an important source of quantum noise at room temperature and at frequencies relevant to gravitational wave detectors. Funded by the National Science Foundation, this work could enable researchers to understand this limiting noise source and test ideas for circumventing it to further increase LIGO’s sensitivity to gravitational waves.

    In addition to future applications for improving LIGO’s detection abilities, Mavalvala says these observations of quantum effects at room temperature could help scientists learn more about how quantum mechanics can disturb the precision of measurements generally — and how best to get around these quantum noise limits.

    “This result was important for the gravitational wave community,” says Mavalvala. “But more broadly, this is essentially a room-temperature quantum resource, and that’s something that many communities should care about.”

    Sensitivity upgrade

    LIGO has undergone upgrades since its first gravitational wave searches in 2002; the currently operating version of the instrumentation is called Advanced LIGO following major upgrades in 2015. But to get LIGO to its maximum design sensitivity, Mavalvala says her team needs to be able to conduct experiments and test improvement strategies in the laboratory rather than on the LIGO instruments themselves. LIGO’s astrophysical detection work is too important to interfere with, so she and her collaborators have developed instruments in the lab that can mimic the sensitivity of the real thing. In this case, the team aimed to reproduce processes that occur in LIGO to measure a type of noise called quantum radiation pressure noise (QRPN).

    In LIGO, gravitational waves are detected by using lasers to probe the motion of mirrors. The mirrors are suspended as pendulums, allowing them to have periodic motion similar to a mass on a spring. When laser beams hit the movable mirrors, the momentum carried by the light applies pressure on the mirror and causes them to move slightly.

    “I like to think of it like a pool table,” says Aggarwal. “When your white cue ball strikes the ball in front of it, the cue ball comes back but it still moves the other ball. When a photon that was traveling forward then travels backwards, the momentum went somewhere; [in this case] that momentum went into the mirror.”

    The quantum nature of light, which is made up of photons, dictates that there are quantum fluctuations in the number of photons hitting the mirrors, creating an uncertain amount of force on the mirrors at any given moment. This uncertainty results in random perturbations of the mirror. When the laser power is high enough, this QRPN can interfere with gravitational wave detection. At Advanced LIGO’s full design sensitivity, with many hundreds of kilowatts of laser power hitting 40-kilogram mirrors, QRPN will become a dominant limitation.

    Minuscule mirrors

    To address this imminent issue, Mavalvala, Aggarwal, and their collaborators designed an experiment to recreate the effects of QRPN in a laboratory setting. One challenge was that the team could not use lasers as powerful as those in Advanced LIGO in their lab experiments. The greater the laser power and the lighter the mass of the mirror oscillator, the stronger the radiation pressure-driven motion. To be able to detect this motion with less laser power, they needed to create an extremely low-mass mirror oscillator. They scaled down the 40-kilogram mirrors of Advanced LIGO with a 100-nanogram mirror oscillator (less than the mass of a grain of salt).

    The team also faced the significant challenge of designing a mirror oscillator that could exhibit quantum behavior at room temperature. Previously, observing quantum effects like QRPN required cryogenic cooling so that the motion due to heat energy of the oscillator would not mask the QRPN. In addition to being challenging and impractical, vibrations associated with cryogenic cooling interferes with LIGO’s operation, so conducting experiments at room temperature would be more readily applicable to LIGO itself. After many iterations of design and testing, Mavalvala and her MIT colleagues designed a mirror oscillator that allowed the team to reach a low enough level of thermally driven fluctuations that the mirror motion was dominated by QRPN at room temperature — the first-ever study to do so.

    “It’s really pretty mind-boggling that we can observe this room-temperature, macroscopic object — you can see it with the naked eye if you squint enough — being pushed around by quantum fluctuations,” Mavalvala says. “Its thermal jitter is small enough that it’s being tickled ever-so-slightly by quantum fluctuations, and we can measure that.”

    This was also the first study to detect QRPN at frequencies relevant to gravitational wave detectors. Their success means that they can now design additional experiments that reflect the radiation pressure conditions in Advanced LIGO itself.

    “This experiment mimics an important noise source in Advanced LIGO,” says Mavalvala. “It’s now a test bed where we can try out new ideas for improving Advanced LIGO without impinging on the instrument’s own operating time.”

    Advanced LIGO does not yet run its lasers at strong enough power for QRPN to be a limiting factor in gravitational wave detections. But, as the instruments become more sensitive, this type of noise will soon become a problem and limit Advanced LIGO’s capabilities. When Mavalvala and her collaborators recognized QRPN as an imminent issue, they strove to recreate its effects in the laboratory so that they can start exploring ways to overcome this challenge.

    “We’ve known for a long time that this QRPN would be a limitation for Advanced LIGO,” says Mavalvala. “Now that we are able to reproduce that effect in a laboratory setting, we can start to test ideas for how to improve that limit.”

    Mavalvala’s primary collaborator at LSU was Thomas Corbitt, an associate professor of physics and astronomy. Corbitt was formerly a graduate student and post-doctoral scholar in Mavalvala’s lab at MIT. They have since collaborated for many years.

    “This is the first time this effect has been observed in a system similar to gravitational wave interferometers and in LIGO’s frequency band,” says Corbitt. “While this work was motivated by the imperative to make ever-more-sensitive gravitational wave detectors, it is of wide interest.”

    New directions

    Since the original detection of a binary black hole merger in 2015, LIGO has also captured signals from collisions of neutron stars, as well as additional black hole collisions. These waves ripple outward from interactions that can take place more than a billion light years away. While LIGO’s capabilities are impressive, Mavalvala and her team plan to continue finding ways to make LIGO even more powerful.

    Before they collide, black holes, for example, orbit each other slowly and at lower frequencies. As the two black holes get closer, their orbits speed up and they swirl around each other at high speeds and high frequencies. If Advanced LIGO becomes sensitive enough to pick up lower frequencies, Mavalvala says we may someday detect these systems earlier in the process, before the pair collides, allowing us to draw an ever-clearer picture of these distant spacetime phenomena. She and her team aim to make sure that factors such as QRPN don’t limit Advanced LIGO’s growing power.

    “At this moment in time, Advanced LIGO is the best it can be at its job: to look out at the sky and detect gravitational wave events,” says Mavalvala. “In parallel, we have all of these ideas for making it better, and we have to be able to try those out in laboratories. This measurement allows that to happen with QRPN for the first time.”

    See the full article here .


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    Please help promote STEM in your local schools.


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  • richardmitnick 11:26 am on April 26, 2019 Permalink | Reply
    Tags: , , , Caltech/MIT Advanced aLigo, , , , IPTA-International Pulsar Timing Array, , , ,   

    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.

    3
    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.

    4
    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 8:16 am on April 26, 2019 Permalink | Reply
    Tags: , , , Caltech/MIT Advanced aLigo, , , LIGO Detects Gravitational Waves From Another Neutron Star Merger,   

    From Discover Magazine: “Breaking: LIGO Detects Gravitational Waves From Another Neutron Star Merger” 

    DiscoverMag

    From Discover Magazine

    April 25, 2019

    1
    An artist’s illustration of two colliding neutron stars. (Credit: NASA/Swift/Dana Berry)

    For just the second time, physicists working on the Laser Interferometer Gravitational-Wave Observatory (LIGO) have caught the gravitational waves of two neutron stars colliding to form a black hole.

    The ripples in space time traveled some 500 million light-years and reached the detectors at LIGO, as well as its Italian sister observatory, Virgo, at around 4 a.m. E.T. on Thursday, April 25. Team members say there’s a more than 99 percent chance that the gravitational waves were created from a binary neutron star merger.


    Shot at a Kilonova

    In the moments after the event, a notice went out alerting astronomers around the world to turn their telescopes to the heavens in hopes of catching light from the explosion, which may have formed an extreme object called a kilonova. Kilonovas are 1,000 times brighter than normal novas, and they create huge amounts of heavy elements, like gold and platinum. That brightness makes it easy for astronomers to find these events in the night sky — provided they’ve been given a heads-up and location from LIGO first.

    LIGO’s twin L-shaped observatories — one in Washington state and one in Louisiana — work by shooting a laser beam down the long legs of their “L.”

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Their experimental setup is precise enough that even the minimal disturbance caused by a passing gravitational wave is enough to trigger a slight change in the laser’s appearance. It made the first ever detection of gravitational waves in 2016. Then it followed up by detecting merging neutron stars in 2017.

    Scientists use any slight delays between when signals reach the detectors to help them better triangulate where the waves originated in the sky. But one of LIGO’s twin detectors was offline Thursday when the gravitational wave reached Earth, making it hard for astronomers to triangulate exactly where the signal was coming from. That sent astronomers racing to image as many galaxies as they could across a region covering one-quarter of the sky.

    And instead of finding one potential binary neutron star merger, astronomers turned up at least two different candidates. Now the question is which, if any, are related to the gravitational wave that LIGO saw. Sorting that out will require more observations, which are already happening around the world as darkness falls.

    “I would assume that every observatory in the world is observing this now,” says astronomer Josh Simon of the Carnegie Observatories. “These two candidates (they’ve) found are relatively close to the equator, so they can be seen from both the Northern and Southern Hemisphere.”

    Simon also says that, as of Thursday afternoon in the United States, telescopes in Europe and elsewhere should be gathering spectra on these objects. His fellow astronomers at the Carnegie Observatories plan to turn their telescopes at Chile’s Las Campanas Observatory to the event as soon as darkness falls Thursday night.

    Carnegie 6.5 meter Magellan Baade and Clay Telescopes located at Carnegie’s Las Campanas Observatory, Chile. over 2,500 m (8,200 ft) high

    History-Making Merger

    LIGO’s first detection of a neutron star merger came in August of 2017, when scientists detected gravitational ripples from a collision that occurred about 130 million light years away. Astronomers around the world immediately turned their telescopes to the collision’s location in the sky, allowing them to gather a range of observations from across the electromagnetic spectrum.

    The 2017 detection was the first time an astronomical event had been observed with both light and gravitational waves, ushering in a new era of “multi-messenger astronomy.” The resulting information gave scientists invaluable data on how heavy elements are created, a direct measurement of the expansion of the universe and evidence that gravitational waves travel at the speed of light, among other things.

    This second observation appears to have been slightly too far away for astronomers to get some of of the data they had hoped for, such as how nuclear matter behaves during the intense explosions.

    2
    Researchers at the Laser Interferometer Gravitational-wave Observatory (LIGO) in Livingston, La., recently upgraded the massive instrument. (Ernie Mastroianni/Discover)

    And astronomers still aren’t sure whether the first detection they made came from a typical neutron star merger or whether it was more exotic. But to figure that out, they’d need observations as early as possible, and precious hours have already passed.

    “After the first event, it was clear that a lot of the action was going on immediately after the explosion, so we wanted to get observations as soon as possible,” Simon says. In this case, with one of LIGO’s detectors down, they couldn’t find the object as quickly as they did in 2017.

    So far, one difference is that, unlike last time, astronomers haven’t spotted any signs of gamma-ray bursts, says University of Wisconsin-Milwaukee physicist Jolien Creighton, a LIGO team member.

    But regardless, having additional observations should help us learn more about these extreme cosmic collisions.

    “It gives us a much better handle on the rate of such collisions,” says Stefan Ballmer, associate physics professor at Syracuse University and LIGO member. “The upshot: if we just observe a little longer we will get the strong signal we are hoping for.”

    LIGO just started its third observing run a few weeks ago. And, in the past, these detections were kept a closely guarded secret until they were confirmed, peer-reviewed and published. But with this latest round, LIGO and Virgo have opened their detections up to the public. In this latest run, LIGO has also already detected three potential black hole collisions, bringing its total lifetime haul to 13.

    See the full article here .

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  • richardmitnick 11:41 am on April 18, 2019 Permalink | Reply
    Tags: "What gravitational waves can say about dark matter", , , , , Caltech/MIT Advanced aLigo, , , , ,   

    From Symmetry: “What gravitational waves can say about dark matter” 

    Symmetry Mag
    From Symmetry

    04/18/19
    Caitlyn Buongiorno

    Scientists think that, under some circumstances, dark matter could generate powerful enough gravitational waves for equipment like LIGO to detect.

    1
    Artwork by Sandbox Studio, Chicago

    In 1916, Albert Einstein published his theory of general relativity, which established the modern view of gravity as a warping of the fabric of spacetime. The theory predicted that objects that interact with gravity could disturb that fabric, sending ripples across it.

    Any object that interacts with gravity can create gravitational waves. But only the most catastrophic cosmic events make gravitational waves powerful enough for us to detect. Now that observatories have begun to record gravitational waves on a regular basis, scientists are discussing how dark matter—only known so far to interact with other matter only through gravity—might create gravitational waves strong enough to be found.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster. But , Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    The spacetime blanket

    In the universe, space and time are invariably linked as four-dimensional spacetime. For simplicity, you can think of spacetime as a blanket suspended above the ground.

    Spacetime with Gravity Probe B. NASA

    Jupiter might be a single Cheerio on top of that blanket. The sun could be a tennis ball. R136a1—the most massive known star—might be a 40-pound medicine ball.

    Each of these objects weighs down the blanket where it sits: the heavier the object, the bigger the dip in the blanket. Like objects of different weights on a blanket, objects of different masses have different effects on the fabric of spacetime. A dip in spacetime is gravitational field.

    The gravitational field of one object can affect another object. The other object might fall into the first object’s gravitational field and orbit around it, like the moon around Earth, or Earth around the sun.

    Alternatively, two bodies with gravitational fields might spiral toward each other, getting closer and closer until they collide. As this happens, they create ripples in spacetime—gravitational waves.

    On September 14, 2015, scientists used the Laser Interferometer Gravitational-Wave Observatory, or LIGO, to make the first direct observation of gravitational waves, part of the buildup to the crash between two massive black holes.

    Since that first detection, the LIGO collaboration—together with the collaboration that runs a partner gravitational-wave observatory called Virgo—has detected gravitational waves from at least 10 more mergers of black holes and, in 2017, the first merger between two neutron stars.


    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)

    Dark matter is believed to be five times as prevalent as visible matter. Its gravitational effects are seen throughout the universe. Scientists think they have yet to definitively see gravitational waves caused by dark matter, but they can think of numerous ways this might happen.

    Primordial black holes

    Scientists have seen the gravitational effects of dark matter, so they know it must be there—or at least, something must be going on to cause those effects. But so far, they’ve never directly detected a dark matter particle, so they’re not sure exactly what dark matter is like.

    One idea is that some of the dark matter could actually be primordial black holes.

    Imagine the universe as an infinitely large petri dish. In this scenario, the Big Bang is the point where matter-bacteria begins to grow. That point quickly expands, moving outward to encompass more and more of the petri dish. If that growth is slightly uneven, certain areas will become more densely inhabited by matter than others.

    These pockets of dense matter—mostly photons at this point in the universe—might have collapsed under their own gravity and formed early black holes.

    “I think it’s an interesting theory, as interesting as a new kind of particle,” says Yacine Ali-Haimoud, an assistant professor of physics at New York University. “If primordial black holes do exist, it would have profound implications on the conditions in the very early universe.”

    By using gravitational waves to learn about the properties of black holes, LIGO might be able to prove or constrain this dark matter theory.

    Unlike normal black holes, primordial black holes don’t have a minimum mass threshold they need to reach in order to form. If LIGO were to see a black hole less massive than the sun, for example, it might be a primordial black hole.

    Even if primordial black holes do exist, it’s doubtful that they account for all of the dark matter in the universe. Still, finding proof of primordial black holes would expand our fundamental understanding of dark matter and how the universe began.

    Neutron star rattles

    Dark matter seems to interact with normal matter only through gravity, but, based on the way known particles interact, theorists think it’s possible that dark matter might also interact with itself.

    If that is the case, dark matter particles might bind together to form dark objects that are as compact as a neutron star.

    We know that stars drastically “weigh down” the fabric of spacetime around them. If the universe were populated with compact dark objects, there would be a chance that at least some of them would end up trapped inside of ordinary matter stars.

    A normal star and a dark object would interact only through gravity, allowing the two to co-exist without much of a fuss. But any disruption to the star—for example, a supernova explosion—could create a rattle-like disturbance between the resulting neutron star and the trapped dark object. If such an event occurred in our galaxy, it would create detectable gravitational waves

    “We understand neutron stars quite well,” says Sanjay Reddy, University of Washington physics professor and senior fellow with the Institute for Nuclear Theory. “If something ‘odd’ happens with gravitational waves, we would know there was potentially something new going on that might involve dark matter.”

    The likelihood that any exist in our solar system is limited. Chuck Horowitz, Maria Alessandra Papa and Reddy recently analyzed LIGO’s data and found no indication of compact dark objects of a specific mass range within Earth, Jupiter or the sun.

    Further gravitational-wave studies could place further constraints on compact dark objects. “Constraints are important,” says Ann Nelson, a physics professor at the University of Washington. “They allow us to improve existing theories and even formulate new ones.”

    Axion stars

    One light dark matter candidate is the axion, named by physicist Frank Wilczek after a brand of detergent, in reference to its ability to tidy up a problem in the theory of quantum chromodynamics.

    Scientists think it could be possible for axions to bind together into axion stars, similar to neutron stars but made up of extremely compact axion matter.

    “If axions exist, there are scenarios where they can cluster together and form stellar objects, like ordinary matter,” says Tim Dietrich, a LIGO-Virgo member and physicist. “We don’t know if axion stars exist, and we won’t know for sure until we find constraints for our models.”

    If an axion star merged with a neutron star, scientists might not be able to tell the difference between the two with their current instruments. Instead, scientists would need to rely on electromagnetic signals accompanying the gravitational wave to identify the anomaly.

    It’s also possible that axions could bunch around a binary black hole or neutron star system. If those stars then merged, the changes in the axion “cloud” would be visible in the gravitational wave signal. A third possibility is that axions could be created by the merger, an action that would be reflected in the signal.

    This month, the LIGO-Virgo collaborations began their third observing run and, with new upgrades, expect to detect a merger event every week.

    Gravitational-wave detectors have already proven their worth in confirming Einstein’s century-old prediction. But there is still plenty that studying gravitational waves can teach us. “Gravitational waves are like a completely new sense for science,” Ali-Haimoud says. “A new sense means new ways to look at all the big questions in physics.”

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 5:25 pm on April 1, 2019 Permalink | Reply
    Tags: , , , , Caltech/MIT Advanced aLigo, , , , Lisa Barsotti, , ,   

    From MIT News: Women in STEM “3 Questions: Lisa Barsotti on the new and improved LIGO” 

    MIT News
    MIT Widget

    From MIT News

    April 1, 2019
    Jennifer Chu

    1
    LIGO laboratory detection site near Hanford in eastern Washington. Image: Caltech/MIT/LIGO Laboratory

    “If we are very lucky, we might observe something new … or maybe even something totally unexpected.”

    The search for infinitely faint ripples in space-time is back in full swing. Today, LIGO, the Laser Interferometer Gravitational-wave Observatory, operated jointly by Caltech and MIT, resumes its hunt for gravitational waves and the immense cosmic phenomena from which they emanate.

    Over the past several months, LIGO’s twin detectors, in Washington and Lousiana, have been offline, undergoing upgrades to their lasers, mirrors, and other components, which will enable the detectors to listen for gravitational waves over a far greater range, out to about 550 million light-years away — around 190 million light-years farther out than before.

    As the LIGO detectors turn back on, they will be joined by Virgo, the European-based counterpart based in Italy, which also turns on today after undergoing upgrades that doubled its sensitivity. With both LIGO and Virgo back online, scientists anticipate that detections of gravitational waves from the farthest reaches of the universe may be a regular occurrence.

    MIT News spoke with LIGO member Lisa Barsotti, principal research scientist at MIT’s Kavli Institute for Astrophysics and Space Research, about the potential discoveries that lie ahead.

    Kavli MIT Institute For Astrophysics and Space Research

    Q: Give us a sense of the new capabilities that the LIGO detectors now have. What sort of upgrades were made?

    A: Both LIGO detectors are coming back online more sensitive than ever before, thanks to a wide range of improvements. In particular, we more than doubled the laser power in the interferometers to reduce one of the LIGO fundamental noise sources — quantum “shot noise,” caused by the uncertainty of the arrival time of photons onto the main photodetector. We also deployed a new technology, “squeezed” light, that uses quantum optics to further reduce shot noise.

    Combined with other upgrades to mitigate technical noises (for example noises introduced by the control scheme or from stray light) we improved the sensitivity to binary neutron stars by 40 percent in each detector, with respect to the past observing run.

    Q: What do these new capabilities mean for you, as a researcher who will be looking through the data from these upgraded detectors?

    A: I am personally very excited to see the LIGO detectors operating with squeezed light! This new technology has been developed here at MIT after many years of research to make it compatible with the very stringent LIGO requirements, and our graduate students have been leading the commissioning of this new system at the observatories. It is particularly rewarding to see that we succeeded in making LIGO better.

    Also, operation at high laser power has been enabled by another upgrade developed and built here at MIT — an “acoustic mode damper” glued to the main LIGO optics that mitigates instabilities originating with high laser power. We are looking forward to seeing many years of work in our labs pay off in this observing run!

    Q: What new phenomena are you hoping to detect, and how soon could you detect them, with these new capabilities?

    A: We hope to detect more binary neutron star systems (so far only one has been detected), and thanks to the improved LIGO sensitivity, we should be able to observe them with high signal-to-noise ratio. And more black holes, obviously! The more sources we detect, the more we can learn about the way these systems form and evolve.

    If we are very lucky, we might observe something new, like a neutron star-black hole system, or maybe even something totally unexpected. Not only are the LIGO detectors better than before — the Virgo detector in Italy more than doubled its sensitivity with respect to the last observing run, and this will improve our ability to localize sources in the sky, facilitating the follow-up of telescopes at multiple wavelengths.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    So, if the last observing run, “O2,” will be remembered as the one that started multimessenger astronomy, I hope the upcoming one, “O3,” will be the one in which multimessenger astronomy becomes the new normal!

    See the full article here .


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  • richardmitnick 9:21 am on March 31, 2019 Permalink | Reply
    Tags: "Here’s What Scientists Hope to Learn as LIGO Resumes Hunting Gravitational Waves", , Caltech/MIT Advanced aLigo, , , Kagra gravitational wave detector,   

    From Discover Magazine: “Here’s What Scientists Hope to Learn as LIGO Resumes Hunting Gravitational Waves” 

    DiscoverMag

    From Discover Magazine

    March 29, 2019
    Korey Haynes

    After a year of downtime to perform hardware upgrades, the Laser Interferometer Gravitational-Wave Observatory (LIGO) is ready for action and will turn on its twin detectors, one in Washington state and the other in Louisiana, on April 1. This time, it will also be joined by the Virgo collaboration based out of Italy, and possibly also by the KAGRA detector in Japan later in the year.


    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)

    Combined with the hardware upgrades, scientists expect these updates to allow LIGO to spot more observations and trace their origins more clearly. In 2016, LIGO made history with the first-ever direct detection of gravitational waves, produced in that case by colliding black holes.

    3
    A wrinkle in space-time confirms Einstein’s gravitation. Credit: Astronomy Magazine

    New Hardware

    “Most of the upgrades have been increasing the amount of laser power that’s used,” says Jolien Creighton, a University of Wisconsin Milwaukee professor and member of the LIGO collaboration. “That’s improved the sensitivity.” Each of LIGO’s detector is a giant L-shape, and instruments wait for passing gravitational waves to distort the length of each arm of the detector, measuring them by bouncing lasers across their lengths. Researchers are also pushing the physical limits of the detector, which Creighton says is limited by the quantum uncertainly principle. To increase sensitivity even more, the experiment will “quantum squeeze” the laser beam. “This puts it into an interesting quantum mechanical state that lets us detect the arm length of the detector,” to even greater precision than before.

    The additional detectors from Virgo and KAGRA will let researchers triangulate sources on the sky more accurately than the two LIGO detectors can manage alone. Virgo will be online throughout the whole next year of observing, while KAGRA is still being commissioned, but could join as early as fall of 2018 [? Don’t ask me, I did not write this].


    KAGRA gravitational wave detector, Kamioka mine in Kamioka-cho, Hida-city, Gifu-prefecture, Japan

    New Detections

    The upgraded LIGO will look for many of the same events it did before: collisions of two black holes, two neutron stars, or mixtures of both. Creighton says he’s personally excited about binary neutron stars, because those systems are the mostly likely to have counterparts that can be observed by traditional observatories at the same time, at wavelengths from radio waves to visible light to gamma rays. “Seeing more of those will give us more insight into the natures of gamma ray bursts and the formation of elements of the universe,” Creighton says. He points out the mergers can also teach astronomers how matter behaves when crunched down denser than an atom’s nucleus, a state that only exists in neutron stars. “The way we can probe that is by watching the interactions of neutron stars just before they merge. It’s a fundamental nuclear physics lab in space.”

    Creighton says he’s confident they’ll see many more events from colliding black holes, a phenomenon LIGO has already observed more than once. “We’re hoping to see a binary of a neutron star and a black hole,” Creighton says, but since no one has ever seen one, it’s hard to calculate how common or rare they are, and what the odds are of LIGO spotting one in the next year. But LIGO will be peering farther into the universe, “so even rare things should start to be observed,” Creighton says.

    Other possible objects LIGO might spy would be a supernova explosion, or an isolated neutron star spinning rapidly. “If it’s not perfectly symmetric, then that rotating distortion would produce gravitational waves,” Creighton says. The signal would be weak but constant, so the longer LIGO looks, the more likely finding a source like this becomes. Even more subtle would be a skywide, low-level reverberation from the Big Bang, similar to the microwave background that exists in radiation, and which researchers suspect might also exist in gravitational waves.

    “There’s always the hope that we’ll see something entirely unexpected,” Creighton adds. “Those are the things that you really can’t predict in any way.”

    LIGO’s upcoming run will last for roughly a year, at which point it will undergo more upgrades for a year, and then hopefully start the cycle over again, prepared to witness even more spectacular and invisible events.

    See the full article here .

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