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  • richardmitnick 8:33 am on May 25, 2019 Permalink | Reply
    Tags: , , , , , , , , Multimessenger astrophysics   

    From European Space Agency: “Two merging black holes” 

    ESA Space For Europe Banner

    From European Space Agency

    1

    20/05/2019

    Black holes are among the most fascinating objects in the Universe. Enclosing huge amounts of mass in relatively small regions, these compact objects have enormous densities that give rise to some of the strongest gravitational fields in the cosmos, so strong that nothing can escape – not even light.

    This artistic impression shows two black holes that are spiralling towards each other and will eventually coalesce. A black hole merger was first detected in 2015 by LIGO, the Laser Interferometer Gravitational-Wave Observatory, which detected the gravitational waves – fluctuations in the fabric of spacetime – created by the giant collision.

    Black holes and gravitational waves are both predictions of Albert Einstein’s general relativity, which was presented in 1915 and remains to date the best theory to describe gravity across the Universe.

    Karl Schwarzschild derived the equations for black holes in 1916, but they remained rather a theoretical curiosity for several decades, until X-ray observations performed with space telescopes could finally probe the highly energetic emission from matter in the vicinity of these extreme objects. The first ever image of a black hole’s dark silhouette, cast against the light from matter in its immediate surrounding, was only captured recently by the Event Horizon Telescope and published just last month.

    As for gravitational waves, it was Einstein himself who predicted their existence from his theory, also in 1916, but it would take another century to finally observe these fluctuations. Since 2015, the ground-based LIGO and Virgo observatories have assembled over a dozen detections, and gravitational-wave astronomy is a burgeoning new field of research.

    But another of Einstein’s predictions found observational proof much sooner: the gravitational bending of light, which was demonstrated only a few years after the theory had appeared, during a total eclipse of the Sun in 1919.

    In the framework of general relativity, any object with mass bends the fabric of spacetime, deflecting the path of anything that passes nearby – including light. An artistic view of this distortion, also known as gravitational lensing, is depicted in this representation of two merging black holes.

    One hundred years ago, astronomers set out to test general relativity, observing whether and by how much the mass of the Sun deflects the light of distant stars. This experiment could only be performed by obscuring the Sun’s light to reveal the stars around it, something that is possible during a total solar eclipse.

    On 29 May 1919, Sir Arthur Eddington observed the distant stars around the Sun during an eclipse from the island of Príncipe, in West Africa, while Andrew Crommelin performed similar observations in Sobral, in the north east of Brazil.

    Eddington/Einstein exibition of gravitational lensing solar eclipse of 29 May 1919

    The results, presented six months later, indicated that stars observed near the solar disc during the eclipse were slightly displaced, with respect to their normal position in the sky, roughly by the amount predicted by Einstein’s theory for the Sun’s mass to have deflected their light.

    “Lights All Askew in the Heavens,” headlined the New York Times in November 1919 to announce the triumph of Einstein’s new theory. This inaugurated a century of exciting experiments investigating gravity on Earth and in space, proving general relativity more and more precisely.

    We have made giant leaps over the past hundred years, but there is still much for us to discover. Athena, ESA’s future X-ray observatory, will investigate in unprecedented detail the supermassive black holes that sit at the centre of galaxies.


    LISA, another future ESA mission, will detect gravitational waves from orbit, looking for the low-frequency fluctuations that are released when two supermassive black holes merge and can only be detected from space.

    ESA/NASA eLISA

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

    Both missions are currently in the study phase, and are scheduled to launch in the early 2030s. If Athena and LISA could operate jointly for at least a few years, they could perform a unique experiment: observing the merger of supermassive black holes both in gravitational waves and X-rays, using an approach known as multi-messenger astronomy.

    We have never observed such a merger before: we need LISA to detect the gravitational waves and tell us where to look in the sky, then we need Athena to observe it with high precision in X-rays to see how the mighty collision affects the gas surrounding the black holes. We don’t know what happens during such a cosmic clash so this experiment, much like the eclipse of 1919 that first proved Einstein’s theory, is set to shake our understanding of gravity and the Universe.

    See the full article here .


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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 9:49 am on May 8, 2019 Permalink | Reply
    Tags: , , , , , , , , , Multimessenger astrophysics, 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 3:39 pm on May 6, 2019 Permalink | Reply
    Tags: , , , , , Multimessenger astrophysics,   

    From Science News: “LIGO [and VIRGO] on the lookout for these 8 sources of gravitational waves” 

    From Science News

    May 6, 2019
    Lisa Grossman

    Astronomers still hope to catch a star going supernova and a bumpy neutron star, among others.

    1
    BANG, CRASH Physicists using the LIGO and Virgo observatories are catching all sorts of cosmic collisions, including of pairs of neutron stars (illustrated). But scientists hope to bag even more exotic quarry. NASA’s Goddard Space Flight Center/CI Lab

    Seekers of gravitational waves are on a cosmic scavenger hunt.

    Since the Advanced Laser Interferometer Gravitational-wave Observatory turned on in 2015, physicists have caught these ripples in spacetime from several exotic gravitational beasts — and scientists want more.

    This week, LIGO and its partner observatory Virgo announced five new possible gravitational wave detections in a single month, making what was once a decades-long goal almost commonplace (SN Online: 5/2/19).

    _____________________________________________________
    Picking up

    In just one month, scientists have already spotted 5 possible gravitational wave events, plotted here as a function of their approximate distance from Earth. That’s compared to 11 events from all previous observations combined. Most detections are from merging black holes, but neutron star mergers (red) are also in the mix. And one event (yellow) might be a mash up between a black hole and a neutron star.

    Gravitational wave detections by LIGO and Virgo are becoming more frequent

    4
    E. Otwell, T. Tibbitts

    _____________________________________________________

    “We’re just beginning to see the field of gravitational wave astronomy open,” LIGO spokesperson Patrick Brady from the University of Wisconsin–Milwaukee said May 2 in a news conference. “Opening up a new window on the universe like this will hopefully bring us a whole new perspective on what’s out there.”

    The speed and pitch of gravitational wave signals allow astronomers to make out what’s stirring up the waves. Here are the sources of gravitational waves that scientists that already have in their nets, and what they’re still hoping to find.
    1. Pairs of colliding black holes

    Status: Found

    7
    SWEET SUCCESS For the first time, physicists have directly observed gravitational waves, caused by two black holes colliding (illustrated here). SXS collaboration.

    2. Pairs of colliding neutron stars

    Status: Found

    3. A neutron star crashing into a black hole

    Status: Maybe

    3
    TOUGH STUFF An exotic substance thought to exist within a type of collapsed star called a neutron star (illustrated) may be stronger than any other known material.
    Casey Reed/Penn State University, Wikimedia Commons

    4. A collision involving an intermediate-mass black hole

    Status: Not yet

    9
    HIDDEN FIGURE An intermediate-mass black hole about 2,200 times as heavy as the sun may lurk at the center of this dense ball of stars, a globular cluster called 47 Tucanae.
    NASA, ESA, Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, J. Mack/STScI, G. Piotto/University of Padua

    5. A bumpy neutron star

    Status: Not yet

    6. Supernova explosions

    Status: Not yet

    LIGO and Virgo might also be able to pick up gravitational waves from supernova explosions, the bright cataclysms at the end of massive stars’ lives.

    6
    SHINE BRIGHT Supernova 1987A shone as a brilliant point of light near the Tarantula Nebula (pink cloud) in the Large Magellanic Cloud, as pictured from an observatory in Chile.

    Supernovas emit many types of light and particles, including ghostly subatomic particles called neutrinos that are born deep in the heart of the explosions (SN: 2/18/17, p. 20). But scientists still don’t know exactly what makes a star explode as a supernova in the first place.

    What they do know is that during a supernova explosion, the central core of the star collapses, and the resulting proto-neutron star gathers material from the remainder of the collapsing core. The turbulence at the surface of the proto-neutron star makes it vibrate like a bell, sending off gravitational waves. That specific gravitational wave signal is strongly related to the strength of the turbulence and the structure of the nascent neutron star, astrophysicist David Radice of Princeton University and colleagues report April 29 in the Astrophysical Journal Letters.

    7. Waves triggered by the Big Bang

    Status: Not yet

    8. New sources?

    Status: Not yet

    LIGO Caltech. LIGO and Virgo detect neutron star smash-ups. May 2, 2019.
    See https://sciencesprings.wordpress.com/2019/05/06/from-mit-caltech-advanced-aligo-ligo-and-virgo-detect-neutron-star-smash-ups/

    See the full article here .


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

    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: , , , , , , , , Multimessenger astrophysics   

    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?", , , , , , , , Multimessenger astrophysics,   

    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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    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.

    Driven by creativity and curiosity, we strive to fulfil our social, cultural and economic obligations to Cardiff, Wales, and the world.

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

    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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    U Maryland Campus

    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: , , , , , , LIGO Detects Gravitational Waves From Another Neutron Star Merger, Multimessenger astrophysics   

    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 3:48 pm on April 16, 2019 Permalink | Reply
    Tags: A bright burst of X-rays has been discovered by NASA's Chandra X-ray Observatory in a galaxy 6.6 billion light years from Earth., , , , Chandra observed the source dubbed XT2 as it suddenly appeared and then faded away after about seven hours., , , , Multimessenger astrophysics, , The neutron star merger produced a new larger neutron star and not a black hole., This event likely signaled the merger of two neutron stars and could give astronomers fresh insight into how neutron stars — dense stellar objects packed mainly with neutrons — are built.   

    From NASA Chandra: “A New Signal for a Neutron Star Collision Discovered” 

    NASA Chandra Banner

    NASA/Chandra Telescope


    From NASA Chandra

    April 16, 2019

    Megan Watzke
    Chandra X-ray Center, Cambridge, Mass.
    617-496-7998
    mwatzke@cfa.harvard.edu

    1
    Credit: X-ray: NASA/CXC/Uni. of Science and Technology of China/Y. Xue et al; Optical: NASA/STScI

    A bright burst of X-rays has been discovered by NASA’s Chandra X-ray Observatory in a galaxy 6.6 billion light years from Earth. This event likely signaled the merger of two neutron stars and could give astronomers fresh insight into how neutron stars — dense stellar objects packed mainly with neutrons — are built.

    When two neutron stars merge they produce jets of high energy particles and radiation fired in opposite directions. If the jet is pointed along the line of sight to the Earth, a flash, or burst, of gamma rays can be detected. If the jet is not pointed in our direction, a different signal is needed to identify the merger.

    The detection of gravitational waves — ripples in spacetime — is one such signal. Now, with the observation of a bright flare of X-rays, astronomers have found another signal, and discovered that two neutron stars likely merged to form a new, heavier and fast-spinning neutron star with an extraordinarily strong magnetic field.

    “We’ve found a completely new way to spot a neutron star merger,” said Yongquan Xue of the University of Science and Technology of China and lead author of a paper appearing in Nature. “The behavior of this X-ray source matches what one of our team members predicted for these events.”

    Chandra observed the source, dubbed XT2, as it suddenly appeared and then faded away after about seven hours.The source is located in the Chandra Deep Field-South, the deepest X-ray image ever taken that contains almost 12 weeks of Chandra observing time, taken at various intervals over several years. The source appeared on March 22nd, 2015 and was discovered later in analysis of archival data.

    “The serendipitous discovery of XT2 makes another strong case that nature’s fecundity repeatedly transcends human imagination,”said co-author Niel Brandt of the Pennsylvania State University and principal investigator of the relevant Chandra Deep Field-South.

    The researchers identified the likely origin of XT2 by studying how its X-ray light varied with time, and comparing this behavior with predictions made in 2013 by Bing Zhang from the University of Nevada in Las Vegas, one of the corresponding authors of the paper. The X-rays showed a characteristic signature that matched those predicted for a newly-formed magnetar — a neutron star spinning around hundreds of times per second and possessing a tremendously strong magnetic field about a quadrillion times that of Earth’s.

    The team think that the magnetar lost energy in the form of an X-ray-emitting wind, slowing down its rate of spin as the source faded. The amount of X-ray emission stayed roughly constant in X-ray brightness for about 30 minutes, then decreased in brightness by more than a factor of 300 over 6.5 hours before becoming undetectable. This showed that the neutron star merger produced a new, larger neutron star and not a black hole.

    This result is important because it gives astronomers a chance to learn about the interior of neutron stars, objects that are so dense that their properties could never be replicated on Earth.

    “We can’t throw neutron stars together in a lab to see what happens, so we have to wait until the Universe does it for us,” said Zhang. “If two neutron stars can collide and a heavy neutron star survives, then this tells us that their structure is relatively stiff and resilient.”

    Neutron star mergers have been prominent in the news since the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves from one in 2017. That source, known as GW170817, produced a burst of gamma rays and an afterglow in light detected by many other telescopes, including Chandra. Xue’s team think that XT2 would also have been a source of gravitational waves, however it occurred before Advanced LIGO started its first observing run, and it was too distant to have been detected in any case.

    Xue’s team also considered whether the collapse of a massive star could have caused XT2, rather than a neutron star merger. The source is in the outskirts of its host galaxy, which aligns with the idea that supernova explosions that left behind the neutron stars kicked them out of the center a few billion years earlier. The galaxy itself also has certain properties — including a low rate of star formation compared to other galaxies of a similar mass — that are much more consistent with the type of galaxy where the merger of two neutron stars is expected to occur.Massive stars are young and are associated with high rates of star formation.

    “The host-galaxy properties of XT2 indeed boost our confidence in explaining its origin,”said co-author Ye Li from Peking University.

    The team estimated the rate at which events like XT2 should occur, and found that it agrees with the rate deduced from the detection of GW170817. However, both estimates are highly uncertain because they depend on the detection of just one object each, so more examples are needed.

    “We’ve started looking at other Chandra data to see if similar sources are present”, said co-author Xuechen Cheng, also of the University of Science and Technology of China. “Just as with this source, the data sitting in archives might contain some unexpected treasures.”

    A paper describing these results appeared in the April 11th issue of Nature.

    Other materials about the findings are available at:
    http://chandra.si.edu

    For more Chandra images, multimedia and related materials, visit:
    http://www.nasa.gov/chandra

    See the full article here.


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    NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.

     
  • richardmitnick 1:16 pm on April 4, 2019 Permalink | Reply
    Tags: , , , , , Multimessenger astrophysics, , The Hubble Constant discrepency, UC Banta Barbra   

    From UC Santa Barbara: “The Standard Siren” 

    UC Santa Barbara Name bloc
    From UC Santa Barbara

    Ten years before the detection of gravitational waves, two KITP postdocs at UC Santa Barbara had a novel idea.

    April 2, 2019
    Harrison Tasoff

    1
    Two neutron stars collide, sending out gravitational waves and electromagnetic radiation detected on Earth in 2017. Photo Credit: Fermilab

    2
    Scott Hughesz. Photo Credit: MIT

    The history of science is filled with stories of enthusiastic researchers slowly winning over skeptical colleagues to their point of view. Astrophysicist Scott Hughes can relate to these tales.

    “For the first 15 or 16 years of my career I was speaking to astronomers, and I always had the impression that they were politely interested in what I had to say, but regarded me as a little bit of a wild-eyed enthusiast who was telling them about a herd of unicorns that my friends and I were raising,” said Hughes.

    “Now,” he continued, “there are people who are going, ‘Ooh, all those unicorns you found, can I use them to solve my problem? Do your unicorns have wings? Are they sparkly?’”

    3
    Daniel Holz. Photo Credit: University of Chicago

    These unicorns are gravitational waves, an area of physics in which Hughes specializes. While working as postdoctoral researchers at UC Santa Barbara’s Kavli Institute for Theoretical Physics (KITP), Hughes and his colleague, Daniel Holz, were among the first to propose using the phenomena, in combination with telescope-based observations, to measure the Hubble constant, a fundamental quantity involved in describing the expansion of the universe.

    As the universe expands, it carries celestial objects away from us. This stretches out the wavelength of light we detect from these objects, causing it to drop in frequency just like a siren on a passing ambulance. The faster the object is receding, the more its light will shift toward the red end of the spectrum. The Hubble constant relates an object’s distance from Earth to this redshift, and thus the object’s speed as it’s carried away.

    One of an astronomer’s best tools for calculating this is a standard candle, any class of objects that always have the same, standard brightness.

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

    If scientists know the brightness of an object, they can determine its distance by measuring how dim it appears to us on Earth.

    For decades scientists have tried to get accurate measurements of the Hubble constant in order to investigate why the universe is expanding, and, in fact, accelerating. This ultimately resolves to measuring objects’ redshifts and matching them with independent measurements of the objects’ distances from us. However, these two most accurate measurements scientists currently have for the Hubble constant disagree — an endless source of frustration for cosmologists.

    A Proposal

    This was the cosmological landscape in the early 2000s when Holz and Hughes held positions as postdoctoral researchers at KITP. “Scott had been thinking about gravitational waves for a while,” said Holz. “He was the expert, and I was much more focused on cosmological questions.” But Hughes’ enthusiasm soon piqued Holz’s curiosity, and the two began to talk about gravitational wave cosmology in the office and on walks along the Santa Barbara bluffs.

    Holz and Hughes credit their close collaboration to the construction of the new wing of Kohn Hall in 2001. Initially, all postdocs at KITP had their own offices, explained Hughes, but the construction forced them to double-up. “Suddenly we were spending a lot more time with each other.”

    A 2002 KITP program on cosmological data fanned the flames of their interest in the topic. By the time Hughes left to join the faculty at MIT, they had finished the first draft of their paper detailing how to calculate the Hubble constant with gravitational waves. After two years gestating they finally published the study in The Astrophysical Journal.

    “I had a great time writing that paper with Scott,” said Holz. “I learned an incredible amount. So much that I was convinced that gravitational waves were the future, and that I should get involved.”

    The idea of using gravitational wave sources to measure the Hubble constant was not new. The concept was first proposed in a visionary paper back in 1986 by Bernard Schutz [Nature]. And a number of other notions regarding gravitational waves were also floating around the literature in the early 2000s. But what Holz and Hughes did was synthesize all these ideas and emphasize the feasibility of combining data from gravitational waves with follow-up observations using light.

    The study also was the first to use the term “standard siren [Nature].” Hughes recalled discussing the paper with Caltech astrophysicist Sterl Phinney, who remarked, “Hmm. Kind of like a standard candle, but you hear it. You should call it a standard siren.” Holz independently had an almost identical conversation with physicist Sean Carroll, a former KITP postdoc himself. Holz and Hughes included the term in their paper, and it stuck. The phrase has since become ubiquitous in cosmology.

    “The term ‘standard siren’ might be our most lasting contribution, Scott,” Holz remarked. “I’ll take it,” laughed Hughes.

    Using gravitational waves to measure the Hubble constant has many advantages over other methods. Certain supernovae provide decent standard candles, “but, as a standard candle, supernovae are not very well understood,” said Holz. “The main thing that makes standard sirens interesting is that they’re understood from first principles, directly from the theory of general relativity.”

    When using standard candles, scientists have to calibrate the distances of certain classes of objects using the information from other ones, effectively leapfrogging their way to a proper distance measurement. Astronomers call this method a “distance ladder,” and errors and uncertainty can creep in at many points in the calculations.

    3
    Getting accurate measurements of distance requires building up a distance ladder using a number of different techniques for various ranges. Photo Credit: MATT PERKO.

    In contrast, gravitational waves can provide a direct measurement of an object’s distance. “You just write down the equations and solve them, and then you’re done,” said Holz. “We’ve tested general relativity for a hundred years; it really works, and it says ‘here’s how far that source is.’ There’s no distance ladder, there’s none of that fiddling around.”

    All the early papers on measuring the Hubble constant using gravitational waves were somewhat speculative, according to Holz. They were proposals for the far future. “We hadn’t even detected gravitational waves yet, much less waves from two neutron stars, much less with an optical counterpart,” he said. But interest and enthusiasm for the technique were growing.

    Hughes remembers colleagues coming up to him after his talks and asking about the likelihood of observing a standard siren in the next decade. He didn’t know, but he did say that with a better understanding of the optical counterpart, they could probably localize an event to within 10-20 square degrees. “And I think if you have that, every piece of large glass on Earth is going to stare at that spot on the sky,” Hughes had said. “And, in the end, that is exactly what happened.”

    And Then It Happened

    On August 17, 2017, less than two years after detecting the first gravitational waves, the LIGO and Virgo observatories recorded a signal from merging neutron stars. Thanks to an alert system, which Holz helped establish, a flurry of activity followed as nearly every major ground and space-based observatory trained their sights on the event. Scientists collected data on the merger in every region of the electromagnetic spectrum.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    Gravity is talking. Lisa will listen. Dialogos of Eide

    ESA/eLISA the future of gravitational wave research

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


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

    “It really is one of those things where, if it had happened before I retired, I would have been happy,” said Hughes. “But it actually happened before I turned 50.”

    Suddenly, gravitational wave cosmology was a real field, and standard sirens were another part of the toolkit. “But for something to become part of the toolkit so quickly? That’s extraordinarily unusual,” said Holz.

    It turns out that cosmologists need another tool, because they currently have two different values for the Hubble constant. Methods using the cosmic microwave background [CMB] — faint light left over from the big bang — yields a value of around 68. Meanwhile, calculations that use Type Ia supernovae — a variety of standard candle [above] — yield a bit more than 73.

    CMB per ESA/Planck

    Although they appear close, the two values actually differ by three standard deviations, and both have fairly tight error bars. The disagreement has cosmologists increasingly concerned as the error bars on these two values only get tighter. It could signal a fundamental problem in our understanding of the universe, and is the subject of a KITP conference this July.

    There are a few intrinsic differences between the two techniques, though. The cosmic microwave background reflects the conditions of the early universe, while the supernovae paint a picture of the current universe. “There’s a chance that maybe something very strange and unexpected has happened between the early and late days of the universe, and that’s why these values don’t agree,” said Holz. But cosmologists simply don’t know for sure.

    Getting another, independent value for the Hubble constant will help clear up this conundrum. “Because it’s so clean and so direct, that measurement will be a very compelling number,” Holz explained. “At the very least, it’ll inform this discussion, if not just completely resolve it.”

    Holz and his colleagues, Hsin-Yu Chen and Maya Fishbach, have just published a paper in the journal Nature, finding that 20 to 30 observations would allow scientists to calculate the Hubble constant to within 2 percent accuracy, tight enough to begin comparing it to the two values from the cosmic microwave background and supernovae.

    This summer, Holz is co-organizing a KITP program on the new era of gravitational wave physics and astrophysics, and the new field of standard siren cosmology will be a major topic of discussion. In fact, Holz also helped organize the KITP rapid response program that brought researchers together shortly after LIGO’s first detection of gravitational waves.

    Holz and Hughes credit their success to their experiences at KITP. “While working together at the KITP the two of us got excited about measuring the Hubble constant using gravitational waves,” said Holz. “And that’s exactly what the KITP is about: bringing different people together with different backgrounds, stirring the pot and seeing what happens.”

    For the past decade Holz’s career has focused on standard siren cosmology. “And the amazing thing is we’ve actually done it,” he said. “I helped write the paper that did the first standard siren measurement ever. This was exactly what Scott and I had hypothesized about years before.”

    “If both of us hadn’t been at the KITP there’s no way I’d be spending a good fraction of my life on LIGO teleconferences right now,” said Holz. “But I wouldn’t have it any other way.”

    See the full article here .


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