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  • richardmitnick 12:44 pm on June 24, 2019 Permalink | Reply
    Tags: "NASA’s Fermi mission reveals record-setting gamma-ray bursts", Advanced Virgo, , , , , ,   

    From Stanford University: “NASA’s Fermi mission reveals record-setting gamma-ray bursts” 

    Stanford University Name
    From Stanford University

    June 13, 2019

    1
    NASA/DOE/FermiLAT Collaboration

    NASA/Fermi Gamma Ray Space Telescope

    NASA/Fermi LAT

    Stanford has played a leading role in compiling Fermi’s gamma-ray bursts catalogs ever since the space observatory launched nearly 11 years ago.

    For 10 years, NASA’s Fermi Gamma-ray Space Telescope has scanned the sky for gamma-ray bursts (GRBs), the universe’s most luminous explosions. A new catalog of the highest-energy blasts provides scientists with fresh insights into how they work.

    “Fermi is an ongoing experiment that keeps producing good science,” said Nicola Omodei, an astrophysicist at Stanford University’s School of Humanities and Sciences. “GRBs are really one of the most spectacular astronomical events that we witness.”

    The catalog was published in the June 13 edition of The Astrophysical Journal. More than 120 authors contributed to the paper, which was led by Omodei and Giacomo Vianello at Stanford, Magnus Axelsson at Stockholm University in Sweden, and Elisabetta Bissaldi at the National Institute of Nuclear Physics and Polytechnic University in Bari, Italy.

    Stanford has played a leading role in compiling Fermi’s GRB catalogs ever since the space observatory launched nearly 11 years ago. “All of the analysis tools and methods that led to the preperation of the catalogs were developed at Stanford and SLAC,” Omodei said. “We’ve continued to refine the analysis techniques and increase the sensitivity of the Fermi Large Area Telescope (LAT) to GRBs. For every GRB, we can characterize its duration, its temporal behavior, and its spectral properties.”

    GRBs emit gamma rays, the highest-energy form of light. Most GRBs occurs when some types of massive stars run out of fuel and collapse to create new black holes. Others happen when two neutron stars, superdense remnants of stellar explosions, merge. Both kinds of cataclysmic events create jetfers of particles that move near the speed of light. The gamma rays are produced in collisions of fast-moving material inside the jets and when the jets interact with the environment around the star.

    Astronomers can distinguish the two GRB classes by the duration of their lower-energy gamma rays. Short bursts from neutron star mergers last less than 2 seconds, while long bursts typically continue for a minute or more. The new catalog, which includes 17 short and 169 long bursts, describes 186 events seen by Fermi’s Large Area Telescope (LAT) LAT over the last 10 years.

    Fermi observes these powerful bursts using two instruments. The LAT sees about one-fifth of the sky at any time and records gamma rays with energies above 30 million electron volts (MeV) — millions of times the energy of visible light. The Gamma-ray Burst Monitor (GBM) sees the entire sky that isn’t blocked by Earth and detects lower-energy emission. All told, the GBM has detected more than 2,300 GRBs so far.

    Included in Fermi’s latest observation set are a number of record-setting and intriguing events, including the shortest burst ever recorded (GRB 081102B, which lasted just one-tenth of a second), the longest burst in the catalog (GRB 160623A, which remained illuminated for 10 hours), and the farthest known burst (GRB 080916C, located 12.2 billion light-years away in the constellation Carina).

    Also included in the new catalog is GRB 170817A, the first burst to have both its light and gravitational waves captured simultaneously. Light from the event — a product of two neutron stars crashing together — was recorded by Fermi’s GBM instrument, while the spacetime ripples it generated were detected by the Laser Interferometer Gravitational Wave Observatory (LIGO), the Virgo interferometer.


    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)

    “Now that LIGO and VIRGO have begun another observation period, the astrophysics community will be on the lookout for more joint GRB and gravitational wave events” said Judy Racusin, a co-author and Fermi deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This catalog was a monumental team effort, and the result helps us learn about the population of these events and prepares us for delving into future groundbreaking finds.”

    The Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Fermi was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

    See the full article here .


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    Please help promote STEM in your local schools.

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    Stanford University campus. No image credit

    Stanford University

    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

    Stanford University Seal

     
  • richardmitnick 9:49 am on May 8, 2019 Permalink | Reply
    Tags: Advanced Virgo, , , , , , , , , , 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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    Please help promote STEM in your local schools.

    Stem Education Coalition

    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", Advanced Virgo, , 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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    Please help promote STEM in your local schools.

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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: Advanced Virgo, , , , , , , ,   

    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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    Please help promote STEM in your local schools.


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    MIT Seal

    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 8:16 am on April 26, 2019 Permalink | Reply
    Tags: Advanced Virgo, , , , , , 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", Advanced Virgo, , , , , , , , ,   

    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 2:34 pm on April 2, 2019 Permalink | Reply
    Tags: Advanced Virgo, , , , , , , , , ,   

    From University of Chicago: “How to use gravitational waves to measure the expansion of the universe” 

    U Chicago bloc

    From University of Chicago

    Mar 28, 2019
    Louise Lerner


    Prof. Daniel Holz discusses a new way to calculate the Hubble constant, a crucial number that measures the expansion rate of the universe and holds answers to questions about the universe’s size, age and history. Video by UChicago Creative

    Ripples in spacetime lead to new way to determine size and age of universe.

    On the morning of Aug. 17, 2017, after traveling for more than a hundred million years, the aftershocks from a massive collision in a galaxy far, far away finally reached Earth.

    These ripples in the fabric of spacetime, called gravitational waves, tripped alarms at two ultra-sensitive detectors called LIGO, sending texts flying and scientists scrambling.


    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)

    One of the scientists was Prof. Daniel Holz at the University of Chicago. The discovery had provided him the information he needed to make a groundbreaking new measurement of one of the most important numbers in astrophysics: the Hubble constant, which is the rate at which the universe is expanding.

    The Hubble constant holds the answers to big questions about the universe, like its size, age and history, but the two main ways to determine its value have produced significantly different results. Now there was a third way, which could resolve one of the most pressing questions in astronomy—or it could solidify the creeping suspicion, held by many in the field, that there is something substantial missing from our model of the universe.

    “In a flash, we had a brand-new, completely independent way to make a measurement of one of the most profound quantities in physics,” said Holz. “That day I’ll remember all my life.”

    As LIGO and its European counterpart VIRGO turn back on on April 1, Holz and other scientists are preparing for more data that could shed light on some of the universe’s biggest questions.

    Universal questions

    We’ve known the universe is expanding for a long time (ever since eminent astronomer and UChicago alum Edwin Hubble made the first measurement of the expansion in 1929, in fact),

    Edwin Hubble looking through a 100-inch Hooker telescope at Mount Wilson in Southern California, 1929 discovers the Universe is Expanding

    but in 1998, scientists were stunned to discover that the rate of expansion is not slowing as the universe ages, but actually accelerating over time. In the following decades, as they tried to precisely determine the rate, it has become apparent that different methods for measuring the rate produce different answers.

    One of the two methods measures the brightness of supernovae–exploding stars– in distant galaxies;

    Standard Candles to measure age and distance of the universe from supernovae NASA

    the other looks at tiny fluctuations in the cosmic microwave background [CMB], the faint light left over from the Big Bang.

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    Scientists have been working for two decades to boost the accuracy and precision for each measurement, and to rule out any effects which might be compromising the results; but the two values still stubbornly disagree by almost 10 percent.

    2
    A neutron star collision causes detectable ripples in the fabric of spacetime, which are called gravitational waves. Photo courtesy of Aurore Simonnet

    Because the supernova method looks at relatively nearby objects, and the cosmic microwave background is much more ancient, it’s possible that both methods are right—and that something profound about the universe has changed since the beginning of time.

    “We don’t know if one or both of the other methods have some kind of systematic error, or if they actually reflect a fundamental truth about the universe that is missing from our current models,” said Holz. “Either is possible.”

    Holz saw the possibility for a third, completely independent way to measure the Hubble constant—but it would depend on a combination of luck and extreme feats of engineering.

    The ‘standard siren’

    In 2005, Holz wrote a paper [NJP] with Scott Hughes of Massachusetts Institute of Technology suggesting that it would be possible to calculate the Hubble constant through a combination of gravitational waves and light. They called these sources “standard sirens,” a nod to “standard candles”, which refers to the supernovae used to make the Hubble constant measurement.

    But first it would take years to develop technology that could pick up something as ephemeral as ripples in the fabric of spacetime. That’s LIGO: a set of enormous, extremely sensitive detectors that are tuned to pick up the gravitational waves that are emitted when something big happens somewhere in the universe.

    The Aug. 17, 2017 waves came from two neutron stars, which had spiraled around and around each other in a faraway galaxy before finally slamming together at close to the speed of light. The collision sent gravitational waves rippling across the universe and also released a burst of light, which was picked up by telescopes on and around Earth.

    Neutron star collision-Robin Dienel-The Carnegie Institution for Science

    3
    Prof. Daniel Holz writes out the formula for the Hubble constant, which measures the rate at which the universe is expanding.

    That burst of light was what sent the scientific world into a tizzy. LIGO had picked up gravitational wave readings before, but all the previous ones were from collisions of two black holes, which can’t be seen with conventional telescopes.

    But they could see the light from the colliding neutron stars, and the combination of waves and light unlocked a treasure trove of scientific riches. Among them were the two pieces of information Holz needed to make his calculation of the Hubble constant.

    How does the method work?

    To make this measurement of the Hubble constant, you need to know how fast an object—like a newly collided pair of neutron stars—is receding away from Earth, and how far away it was to begin with. The equation is surprisingly simple. It looks like this: The Hubble constant is the velocity of the object divided by the distance to the object, or H=v/d.

    Somewhat counterintuitively, the easiest part to calculate is how fast the object is moving. Thanks to the bright afterglow given off by the collision, astronomers could point telescopes at the sky and pinpoint the galaxy where the neutron stars collided. Then they can take advantage of a phenomenon called redshift: As a faraway object moves away from us, the color of the light it’s giving off shifts slightly towards the red end of the spectrum. By measuring the color of the galaxy’s light, they can use this reddening to estimate how fast the galaxy is moving away from us. This is a century-old trick for astronomers.

    The more difficult part is getting an accurate measure of the distance to the object. This is where gravitational waves come in. The signal the LIGO detectors pick up gets interpreted as a curve, like this:

    4
    The signal picked up by the LIGO detector in Louisiana, as it caught the waves from two neutron stars colliding far away in space, forms a distinctive curve. Courtesy of LIGO

    The shape of the signal tells scientists how big the two stars were and how much energy the collision gave off. By comparing that with how strong the waves were when they reached Earth, they could infer how far away the stars must have been.

    The initial value from just this one standard siren came out to be 70 kilometers per second per megaparsec. That’s right in between the other two methods, which find about 73 (from the supernova method) and 67 (from the cosmic microwave background).

    Of course, that initial standard siren measurement is only from one data point, and large uncertainties remain. But the LIGO detectors are turning back on after an upgrade to boost their sensitivity. Nobody knows how often neutron stars collide, but Holz (along with former student Hsin-Yu Chen and current student Maya Fishbach) wrote a paper estimating that the gravitational wave method may provide a revolutionary, extremely precise measurement of the Hubble constant within five years.

    “As time goes on, we’ll observe more and more of these binary neutron star mergers, and use them as standard sirens to steadily improve our estimate of the Hubble constant. Depending on where our value falls, we might confirm one method or the other. Or we might find an entirely different value,” Holz said. “No matter what we find, it’s gonna be interesting—and will be an important step in learning more about our universe.”

    See the full article here .

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    U Chicago Campus

    An intellectual destination

    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

    The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

    We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with UChicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

    UChicago research has led to such breakthroughs as discovering the link between cancer and genetics, establishing revolutionary theories of economics, and developing tools to produce reliably excellent urban schooling. We generate new insights for the benefit of present and future generations with our national and affiliated laboratories: Argonne National Laboratory, Fermi National Accelerator Laboratory, and the Marine Biological Laboratory in Woods Hole, Massachusetts.

    The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

    In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts.

     
  • richardmitnick 5:25 pm on April 1, 2019 Permalink | Reply
    Tags: Advanced Virgo, , , , , , , , 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", Advanced Virgo, , , , 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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  • richardmitnick 1:33 pm on March 30, 2019 Permalink | Reply
    Tags: Advanced Virgo, , , , , , , , ,   

    From Ethan Siegel: “Ask Ethan: Why Haven’t We Found Gravitational Waves In Our Own Galaxy?” 

    From Ethan Siegel
    Mar 30, 2019

    Artist’s iconic conception of two merging black holes similar to those detected by LIGO Credit LIGO-Caltech/MIT/Sonoma State /Aurore Simonnet

    LIGO and Virgo have now detected a total of 11 binary merger events.


    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 exactly 0 were in the Milky Way. Here’s why.

    One of the most spectacular recent advances in all of science has been our ability to directly detect gravitational waves. With the unprecedented power and sensitivity of the LIGO and Virgo gravitational waves observatories at our disposal, these powerful ripples in the fabric of spacetime are no longer passing by undetected. Instead, for the first time, we’re able to not only observe them, but to pinpoint the location of the sources that generate them and learn about their properties. As of today, 11 separate sources have been detected.

    But they’re all so far away! Why is that? That’s the question of Amitava Datta and Chayan Chatterjee, who ask:

    Why are all the known gravitational wave sources (coalescing binaries) in the distant universe? Why none has been detected in our neighborhood? […] My guess (which is most probably wrong) is that the detectors need to be precisely aligned for any detection. Hence all the detection until now are serendipitous.

    Let’s find out.

    The way observatories like LIGO and Virgo work is that they have two long, perpendicular arms that have the world’s most perfect vacuum inside of them. Laser light of the same frequency is broken up to travel down these two independent paths, reflected back and forth a number of times, and recombined together at the end.

    Light is just an electromagnetic wave, and when you combine multiple waves together, they generate an interference pattern. If the interference is constructive, you see one type of pattern; if it’s destructive, you see a different type. When LIGO and Virgo just hang out, normally, with no gravitational waves going through them, what you see is a relatively steady pattern, with only the random noise (mostly generated by the Earth itself) of the instruments to contend with.

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

    But if you were to change the length of one of these arms relative to the other, the amount of time the light spent traveling down that arm would also change. Because light is a wave, a small change in the time light travels means you’re at a different point in the wave’s crest/trough pattern, and therefore the interference pattern that gets created by combining it with another light wave will change.

    There could be many causes for a single arm to change: seismic noise, a jackhammer across the street, or even a passing truck miles away. But there’s an astrophysical source that could cause that change too: a passing gravitational wave.

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    When a gravitational wave passes through a location in space, it causes an expansion and a compression at alternate times in alternate directions, causing laser arm-lengths to change in mutually perpendicular orientations. Exploiting this physical change is how we developed successful gravitational wave detectors such as LIGO and Virgo. (ESA–C.CARREAU)

    There are two keys that enable us to determine what’s a gravitational wave from what’s mere terrestrial noise.

    Gravitational waves, when they pass through a detector, will cause both arms to change their distance together in opposite directions by a particular, in-phase amount. When you see a periodic pattern of arm lengths oscillating, you can place meaningful constraints on whether your signal was likely to be a gravitational wave or just an Earth-based source of noise.
    We build multiple detectors at different points on Earth. While each one will experience its own noise due to its local environment, a passing gravitational wave will have very similar effects on each of the detectors, separated by at most milliseconds in time.

    As you can see from the very first robust detection of these waves, dating back to observations taken on September 14, 2015, both effects are present.

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    The inspiral and merger of the first pair of black holes ever directly observed. The total signal, along with the noise (top) clearly matches the gravitational wave template from merging and inspiraling black holes of a particular mass (middle). Note how the frequency and amplitude change at the very end-stage of the merger. (B. P. ABBOTT ET AL. (LIGO SCIENTIFIC COLLABORATION AND VIRGO COLLABORATION))

    If we come forward to the present day, we’ve actually detected a large number of mergers: 11 separate ones thus far. Events seem to come in at random, as it’s only the very final stages of inspiral and merger — the final seconds or even milliseconds before two black holes or neutron stars collide — that have the right properties to be picked up by even our most sensitive detectors.

    If we look at the distances to these objects, though, we find something that might trouble us a little bit. Even though our gravitational wave detectors are more sensitive to objects the closer they are to us, the majority of objects we’ve found are many hundreds of millions or even billions of light-years away.

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    The 11 gravitational wave events detected by LIGO and Virgo, with their names, mass parameters, and other essential information encoded in Table form. Note how many events came in the last month of the second run: when LIGO and Virgo were operating simultaneously. The parameter dL is the luminosity distance; the closest object being the neutron star-neutron star merger of 2017, which corresponds to a distance of ~130 million light-years. (THE LIGO SCIENTIFIC COLLABORATION, THE VIRGO COLLABORATION; ARXIV:1811.12907)

    Why is this? If gravitational wave detectors are more sensitive to closer objects, shouldn’t we be detecting them more frequently, in defiance of what we’ve actually observed?

    There are a lot of potential explanations that could account for this mismatch between what you’d expect or not. As our questioners proposed, perhaps it’s due to orientation? After all, there are many phenomena in this Universe, such as pulsars or blazars, that only appear visible to us when the correct electromagnetic signal gets “beamed” directly to our line-of-sight.

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    Artist’s impression of an active galactic nucleus. The supermassive black hole at the center of the accretion disk sends a narrow high-energy jet of matter into space, perpendicular to the disc. A blazar about 4 billion light years away is the origin of many of the highest-energy cosmic rays and neutrinos. Only matter from outside the black hole can leave the black hole; matter from inside the event horizon can ever escape. (DESY, SCIENCE COMMUNICATION LAB)

    It’s a clever idea, but it misses a fundamental difference between the gravitational and electromagnetic forces. In electromagnetism, electromagnetic radiation gets generated by the acceleration of charged particles; in General Relativity, gravitational radiation (or gravitational waves) are generated by the acceleration of massive particles. So far, so good.

    But there are both electric and magnetic fields in electromagnetism, and electrically charged particles in motion generate magnetic fields. This allows you to create and accelerate particles and radiation in a collimated fashion; it doesn’t have to spread out in a spherical pattern. In gravitation, though, there are only gravitational sources (masses and energetic quanta) and the curvature of spacetime that results.

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    When you have two gravitational sources (i.e., masses) inspiraling and eventually merging, this motion causes the emission of gravitational waves. Although it might not be intuitive, a gravitational wave detector will be sensitive to these waves as a function of 1/r, not as 1/r², and will see those waves in all directions, regardless of whether they’re face-on or edge-on, or anywhere in between. (NASA, ESA, AND A. FEILD (STSCI))

    As it turns out, it doesn’t really matter whether we see an inspiraling and merging gravitational wave source face-on, edge-on, or at an angle; they still emit gravitational waves of a measurable and observable frequency and amplitude. There may be subtle differences in the magnitude and other properties of the signal that arrives at our eyes that are orientation-dependent, but gravitational waves propagate spherically outward from a source that generates them, and can literally be seen from anywhere in the Universe so long as your detector is sensitive enough.

    So why is it, then, that there aren’t gravitational waves from binary sources detected in our own galaxy?

    It might surprise you to learn that there are binary sources of mass, like black holes and neutron stars, orbiting and inspiraling right now.

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    From the very first binary neutron star system ever discovered, we knew that gravitational radiation was carrying energy away. It was only a matter of time before we found a system in the final stages of inspiral and merger. (NASA (L), MAX PLANCK INSTITUTE FOR RADIO ASTRONOMY / MICHAEL KRAMER)

    Long before gravitational waves were directly detected, we spotted what we thought was an ultra-rare configuration: two pulsars orbiting one another. We watched their pulse time vary in a way that showcased their orbital decay due to gravitational radiation. Many pulsars, including multiple binary pulsars, have since been observed. In every case where we’ve been able to measure them accurately enough, we see the orbital decay that shows yes, they are emitting gravitational waves.

    Women in STEM – Dame Susan Jocelyn Bell Burnell

    Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

    Dame Susan Jocelyn Bell Burnell at work on first plusar chart 1967 pictured working at the Four Acre Array in 1967. Image courtesy of Mullard Radio Astronomy Observatory.

    Dame Susan Jocelyn Bell Burnell 2009

    Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

    Similarly, we’ve observed X-ray emissions from systems that indicate there must be a black hole at the center. While binary black holes have only been discovered in two instances from electromagnetic observations, the stellar-mass black holes we know of have been discovered as they accrete or siphon matter from a companion star: the X-ray binary scenario.

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

    These systems are:

    abundant within the Milky Way,
    inspiraling and radiating gravitational waves away to conserve energy,
    which means there are gravitational waves of specific frequencies and amplitudes passing through our detectors,
    with the sources generating those signals destined to someday merge and complete their coalescence.

    But again, we have not observed them in our ground-based gravitational wave detectors. And there’s a simple, straightforward reason for that: our detectors are in the wrong frequency range!

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

    It’s only in the very, very last seconds of coalescence that gravitational waves from merging binaries fall into the LIGO/Virgo sensitivity range. For all the millions or even billions of years that neutron stars or black holes orbit one another and see their orbits decay, they do so at larger radial separations, which means they take longer to orbit each other, which means lower frequency gravitational waves.

    The reason we don’t see the binaries orbiting in our galaxy today is because LIGO’s and Virgo’s arms are too short! If they were millions of kilometers long instead of 3–4 km with many reflections, we’d have already seen them. As it stands right now, this will be a significant advance of LISA [above]: it can show us these binaries that are destined to merge in the future, even enabling us to predict where and when it will happen!

    It’s true: during the time that LIGO and Virgo have been operating, we haven’t seen any mergers of black holes or neutron stars in our own galaxy. This is no surprise; the results from our gravitational wave observations have taught us that there are somewhere around 800,000 merging black hole binaries throughout the Universe in any year. But there are two trillion galaxies in the Universe, meaning that we need to observe millions of galaxies in order to just get one event!

    This is why our gravitational wave observatories need to be sensitive to distances that go out billions of light-years in all directions; there simply won’t be enough statistics otherwise.

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    The range of Advanced LIGO and its capability of detecting merging black holes. Note that even though the amplitude of the waves will fall off as 1/r, the number of galaxies increases with volume: as r³. (LIGO COLLABORATION / AMBER STUVER / RICHARD POWELL / ATLAS OF THE UNIVERSE)

    There are plenty of neutron stars and black holes orbiting one another all throughout the Universe, including right here in our own Milky Way galaxy. When we look for these systems, with either radio pulses (for the neutron stars) or X-rays (for the black holes), we find them in great abundances. We can even see the evidence for the gravitational waves they emit, although the evidence we see is indirect.

    If we had more sensitive, lower-frequency gravitational wave observatories, we could potentially detect the waves generated by sources within our own galaxy directly. But if we want to get a true merger event, those are rare. They might be aeons in the making, but the actual events themselves take just a fraction of a second. It’s only by casting a very wide net that we can see them at all. Incredibly, the technology to do so is already here.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

     
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