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  • richardmitnick 4:03 pm on January 14, 2020 Permalink | Reply
    Tags: , , , Collisions of supermassive black holes may be simultaneously observable in both gravitational waves and X-rays at the beginning of the next decade., , , , Gravitational wave astronomy, ,   

    From University of Birmingham UK: “X-rays and gravitational waves will combine to illuminate massive black hole collisions” 

    From University of Birmingham UK

    14 Jan 2020
    Beck Lockwood, Press Office
    University of Birmingham UK
    tel: +44 (0)121 414 2772.
    r.lockwood@bham.ac.uk

    A new study by a group of researchers at the University of Birmingham has found that collisions of supermassive black holes may be simultaneously observable in both gravitational waves and X-rays at the beginning of the next decade.

    1
    An image of the use of Athena and LISA to observe the same source. Credits: R.Buscicchio (University of Birmingham), based on content from NASA, ESA, IFCA, the Athena Community Office, G. Alexandrov, A. Burrows

    ESA/Athena spacecraft depiction

    Gravity is talking. Lisa will listen. Dialogos of Eide


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

    The European Space Agency (ESA) has recently announced that its two major space observatories of the 2030s will have their launches timed for simultaneous use. These missions, Athena, the next generation X-ray space telescope and LISA, the first space-based gravitational wave observatory, will be coordinated to begin observing within a year of each other and are likely to have at least four years of overlapping science operations.

    According to the new study, published this week in Nature Astronomy, ESA’s decision will give astronomers an unprecedented opportunity to produce multi-messenger maps of some of the most violent cosmic events in the Universe, which have not been observed so far and which lie at the heart of long-standing mysteries surrounding the evolution of the Universe.

    They include the collision of supermassive black holes in the core of galaxies in the distant universe and the “swallowing up” of stellar compact objects such as neutron stars and black holes by massive black holes harboured in the centres of most galaxies.

    The gravitational waves measured by LISA will pinpoint the ripples of space time that the mergers cause while the X-rays observed with Athena reveal the hot and highly energetic physical processes in that environment. Combining these two messengers to observe the same phenomenon in these systems would bring a huge leap in our understanding of how massive black holes and galaxies co-evolve, how massive black holes grow their mass and accrete, and the role of gas around these black holes.

    These are some of the big unanswered questions in astrophysics that have puzzled scientists for decades.

    Dr Sean McGee, Lecturer in Astrophysics at the University of Birmingham and a member of both the Athena and LISA consortiums, led the study. He said, “The prospect of simultaneous observations of these events is uncharted territory, and could lead to huge advances. This promises to be a revolution in our understanding of supermassive black holes and how they growth within galaxies.”

    Professor Alberto Vecchio, Director of the Institute for Gravitational Wave Astronomy, University of Birmingham, and a co-author on the study, said: “I have worked on LISA for twenty years and the prospect of combining forces with the most powerful X-ray eyes ever designed to look right at the centre of galaxies promises to make this long haul even more rewarding. It is difficult to predict exactly what we’re going to discover: we should just buckle up, because it is going to be quite a ride”.

    During the life of the missions, there may be as many as 10 mergers of black holes with masses of 100,000 to 10,000,000 times the mass of the sun that have signals strong enough to be observed by both observatories. Although due to our current lack of understanding of the physics occurring during these mergers and how frequently they occur, the observatories could observe many more or many fewer of these events. Indeed, these are questions which will be answered by the observations.

    In addition, LISA will detect the early stages of stellar mass black holes mergers which will conclude with the detection in ground based gravitational wave observatories. This early detection will allow Athena to be observing the binary location at the precise moment the merger will occur.

    See the full article here .

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    Birmingham has been challenging and developing great minds for more than a century. Characterised by a tradition of innovation, research at the University has broken new ground, pushed forward the boundaries of knowledge and made an impact on people’s lives. We continue this tradition today and have ambitions for a future that will embed our work and recognition of the Birmingham name on the international stage.

     
  • richardmitnick 2:12 pm on January 7, 2020 Permalink | Reply
    Tags: "LIGO-Virgo Network Catches Another Neutron Star Collision", , , , , , Gravitational wave astronomy, ,   

    From MIT Caltech Advanced aLIGO and Advanced Virgo: “LIGO-Virgo Network Catches Another Neutron Star Collision” 

    MIT /Caltech Advanced aLigo


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    From MIT Caltech Advanced aLIGO and Advanced Virgo

    January 6, 2020

    Caltech
    Whitney Clavin
    wclavin@caltech.edu

    MIT
    Abigail Abazorius
    abbya@mit.edu
    617-253-2709

    Virgo
    Livia Conti
    livia.conti@pd.infn.it

    NSF
    Josh Chamot
    jchamot@nsf.gov
    703-292-4489

    1
    Artist’s rendition of two colliding neutron stars. Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet

    On April 25, 2019, the LIGO Livingston Observatory picked up what appeared to be gravitational ripples from a collision of two neutron stars. LIGO Livingston is part of a gravitational-wave network that includes LIGO (the Laser Interferometer Gravitational-wave Observatory), funded by the National Science Foundation (NSF), and the European Virgo detector. Now, a new study confirms that this event was indeed likely the result of a merger of two neutron stars. This would be only the second time this type of event has ever been observed in gravitational waves.

    The first such observation, which took place in August of 2017, made history for being the first time that both gravitational waves and light were detected from the same cosmic event. The April 25 merger, by contrast, did not result in any light being detected. However, through an analysis of the gravitational-wave data alone, researchers have learned that the collision produced an object with an unusually high mass.

    “From conventional observations with light, we already knew of 17 binary neutron star systems in our own galaxy and we have estimated the masses of these stars,” says Ben Farr, a LIGO team member based at the University of Oregon. “What’s surprising is that the combined mass of this binary is much higher than what was expected.”

    “We have detected a second event consistent with a binary neutron star system and this is an important confirmation of the August 2017 event that marked an exciting new beginning for multi-messenger astronomy two years ago,” says Jo van den Brand, Virgo Spokesperson and professor at Maastricht University, and Nikhef and VU University Amsterdam in the Netherlands. Multi-messenger astronomy occurs when different types of signals are witnessed simultaneously, such as those based on gravitational waves and light.

    The study, submitted to The Astrophysical Journal Letters, is authored by an international team comprised of the LIGO Scientific Collaboration and the Virgo Collaboration, the latter of which is associated with the Virgo gravitational-wave detector in Italy. The results were presented at a press briefing today, January 6, at the 235th meeting of the American Astronomical Society in Honolulu, Hawaii.

    One of two science papers:
    GW190425

    On January 6, 2020, the LIGO Scientific Collaboration and the Virgo Collaboration announced the discovery of a second binary neutron star merger, labeled GW190425. This is the first confirmed gravitational-wave detection based on data from a single observatory. No electromagnetic counterpart was found. This system is notable for having a total mass that exceeds that of known galactic neutron star binaries.
    Publications & Documents

    Publication: GW190425: Observation of a compact binary coalescence with total mass ∼3.4 Msun

    The other paper hasn’t been accepted or published yet and may be a while.

    Neutron stars are the remnants of dying stars that undergo catastrophic explosions as they collapse at the end of their lives. When two neutron stars spiral together, they undergo a violent merger that sends gravitational shudders through the fabric of space and time.

    LIGO became the first observatory to directly detect gravitational waves in 2015; in that instance, the waves were generated by the fierce collision of two black holes. Since then, LIGO and Virgo have registered dozens of additional candidate black hole mergers.

    The August 2017 neutron star merger was witnessed by both LIGO detectors, one in Livingston, Louisiana, and one in Hanford, Washington, together with a host of light-based telescopes around the world (neutron star collisions produce light, while black hole collisions are generally thought not to do so). This merger was not clearly visible in the Virgo data, but that fact provided key information that ultimately pinpointed the event’s location in the sky.

    The April 2019 event was first identified in data from the LIGO Livingston detector alone. The LIGO Hanford detector was temporarily offline at the time, and, at a distance of more than 500 million light-years, the event was too faint to be visible in Virgo’s data. Using the Livingston data, combined with information derived from Virgo’s data, the team narrowed the location of the event to a patch of sky more than 8,200 square degrees in size, or about 20 percent of the sky. For comparison, the August 2017 event was narrowed to a region of just 16 square degrees, or 0.04 percent of the sky.

    “This is our first published event for a single-observatory detection,” says Caltech’s Anamaria Effler, a scientist who works at LIGO Livingston. “But Virgo made a valuable contribution. We used information about its non-detection to tell us roughly where the signal must have originated from.”

    The LIGO data reveal that the combined mass of the merged bodies is about 3.4 times the mass of our sun. In our galaxy, known binary neutron star systems have combined masses up to only 2.9 times that of sun. One possibility for the unusually high mass is that the collision took place not between two neutron stars, but a neutron star and a black hole, since black holes are heavier than neutron stars. But if this were the case, the black hole would have to be exceptionally small for its class. Instead, the scientists believe it is much more likely that LIGO witnessed a shattering of two neutron stars.

    “What we know from the data are the masses, and the individual masses most likely correspond to neutron stars. However, as a binary neutron star system, the total mass is much higher than any of the other known galactic neutron star binaries,” says Surabhi Sachdev, a LIGO team member based at Penn State. “And this could have interesting implications for how the pair originally formed.”

    Neutron star pairs are thought to form in two possible ways. They might form from binary systems of massive stars that each end their lives as neutron stars, or they might arise when two separately formed neutron stars come together within a dense stellar environment. The LIGO data for the April 25 event do not indicate which of these scenarios is more likely, but they do suggest that more data and new models are needed to explain the merger’s unexpectedly high mass.

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    See the full article here .

    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.


    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 10:17 am on December 29, 2019 Permalink | Reply
    Tags: , , , , , Gravitational wave astronomy, , ,   

    From particlebites: “Dark Photons in Light Places” 

    particlebites bloc

    From particlebites

    December 29, 2019
    Amara McCune

    Title: “Searching for dark photon dark matter in LIGO O1 data”

    Author: Huai-Ke Guo, Keith Riles, Feng-Wei Yang, & Yue Zhao

    Reference: https://www.nature.com/articles/s42005-019-0255-0

    There is very little we know about dark matter save for its existence.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., 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 LSST, or Large Synoptic Survey Telescope is to be named the Vera C. Rubin Observatory by an act of the U.S. Congress.

    LSST telescope, The Vera Rubin Survey Telescope currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    Dark Matter Research

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Scientists studying the cosmic microwave background [CMB] hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

    CMB per ESA/Planck

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LBNL LZ Dark Matter project at SURF, Lead, SD, USA


    Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington. Axion Dark Matter Experiment

    Its mass(es), its interactions, even the proposition that it consists of particles at all is mostly up to the creativity of the theorist. For those who don’t turn to modified theories of gravity to explain the gravitational effects on galaxy rotation and clustering that suggest a massive concentration of unseen matter in the universe (among other compelling evidence), there are a few more widely accepted explanations for what dark matter might be. These include weakly-interacting massive particles (WIMPS), primordial black holes, or new particles altogether, such as axions or dark photons.

    In particle physics, this latter category is what’s known as the “hidden sector,” a hypothetical collection of quantum fields and their corresponding particles that are utilized in theorists’ toolboxes to help explain phenomena such as dark matter. In order to test the validity of the hidden sector, several experimental techniques have been concocted to narrow down the vast parameter space of possibilities, which generally consist of three strategies:

    1.Direct detection: Detector experiments look for low-energy recoils of dark matter particle collisions with nuclei, often involving emitted light or phonons.
    2.Indirect detection: These searches focus on potential decay products of dark matter particles, which depends on the theory in question.
    3.Collider production: As the name implies, colliders seek to produce dark matter in order to study its properties. This is reliant on the other two methods for verification.

    The first detection of gravitational waves from a black hole merger in 2015 ushered in a new era of physics, in which the cosmological range of theory-testing is no longer limited to the electromagnetic spectrum.

    MIT /Caltech Advanced aLigo


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

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

    Caltech/MIT Advanced aLigo detector installation Hanford, WA, USA

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Gravity is talking. Lisa will listen. Dialogos of Eide

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

    Bringing LIGO (the Laser Interferometer Gravitational-Wave Observatory) to the table, proposals for the indirect detection of dark matter via gravitational waves began to spring up in the literature, with implications for primordial black hole detection or dark matter ensconced in neutron stars. Yet a new proposal, in a paper by Guo et. al., [Scientific Reports-Communication Physics] suggests that direct dark matter detection with gravitational waves may be possible, specifically in the case of dark photons.

    Dark photons are hidden sector particles in the ultralight regime of dark matter candidates. Theorized as the gauge boson of a U(1) gauge group, meaning the particle is a force-carrier akin to the photon of quantum electrodynamics, dark photons either do not couple or very weakly couple to Standard Model particles in various formulations. Unlike a regular photon, dark photons can acquire a mass via the Higgs mechanism. Since dark photons need to be non-relativistic in order to meet cosmological dark matter constraints, we can model them as a coherently oscillating background field: a plane wave with amplitude determined by dark matter energy density and oscillation frequency determined by mass. In the case that dark photons weakly interact with ordinary matter, this means an oscillating force is imparted. This sets LIGO up as a means of direct detection due to the mirror displacement dark photons could induce in LIGO detectors.

    3
    Figure 1: The experimental setup of the Advanced LIGO interferometer. We can see that light leaves the laser and is reflected between a few power recycling mirrors (PR), split by a beam splitter (BS), and bounced between input and end test masses (ITM and ETM). The entire system is mounted on seismically-isolated platforms to reduce noise as much as possible. Source: https://arxiv.org/pdf/1411.4547.pdf

    LIGO consists of a Michelson interferometer, in which a laser shines upon a beam splitter which in turn creates two perpendicular beams. The light from each beam then hits a mirror, is reflected back, and the two beams combine, producing an interference pattern. In the actual LIGO detectors, the beams are reflected back some 280 times (down a 4 km arm length) and are split to be initially out of phase so that the photodiode detector should not detect any light in the absence of a gravitational wave. A key feature of gravitational waves is their polarization, which stretches spacetime in one direction and compresses it in the perpendicular direction in an alternating fashion. This means that when a gravitational wave passes through the detector, the effective length of one of the interferometer arms is reduced while the other is increased, and the photodiode will detect an interference pattern as a result.

    LIGO has been able to reach an incredible sensitivity of one part in 10^{23} in its detectors over a 100 Hz bandwidth, meaning that its instruments can detect mirror displacements up to 1/10,000th the size of a proton. Taking advantage of this number, Guo et. al. demonstrated that the differential strain (the ratio of the relative displacement of the mirrors to the interferometer’s arm length, or h = \Delta L/L) is also sensitive to ultralight dark matter via the modeling process described above. The acceleration induced by the dark photon dark matter on the LIGO mirrors is ultimately proportional to the dark electric field and charge-to-mass ratio of the mirrors themselves.

    Once this signal is approximated, next comes the task of estimating the background. Since the coherence length is of order 10^9 m for a dark photon field oscillating at order 100 Hz, a distance much larger than the separation between the LIGO detectors at Hanford and Livingston (in Washington and Louisiana, respectively), the signals from dark photons at both detectors should be highly correlated. This has the effect of reducing the noise in the overall signal, since the noise in each of the detectors should be statistically independent. The signal-to-noise ratio can then be computed directly using discrete Fourier transforms from segments of data along the total observation time. However, this process of breaking up the data, known as “binning,” means that some signal power is lost and must be corrected for.

    4
    Figure 2: The end result of the Guo et. al. analysis of dark photon-induced mirror displacement in LIGO. Above we can see a plot of the coupling of dark photons to baryons as a function of the dark photon oscillation frequency. We can see that over further Advanced LIGO runs, up to O4-O5, these limits are expected to improve by several orders of magnitude. Source: https://www.nature.com/articles/s42005-019-0255-0

    In applying this analysis to the strain data from the first run of Advanced LIGO, Guo et. al. generated a plot which sets new limits for the coupling of dark photons to baryons as a function of the dark photon oscillation frequency. There are a few key subtleties in this analysis, primarily that there are many potential dark photon models which rely on different gauge groups, yet this framework allows for similar analysis of other dark photon models. With plans for future iterations of gravitational wave detectors, further improved sensitivities, and many more data runs, there seems to be great potential to apply LIGO to direct dark matter detection. It’s exciting to see these instruments in action for discoveries that were not in mind when LIGO was first designed, and I’m looking forward to seeing what we can come up with next!

    Learn More:

    An overview of gravitational waves and dark matter: https://www.symmetrymagazine.org/article/what-gravitational-waves-can-say-about-dark-matter
    A summary of dark photon experiments and results: https://physics.aps.org/articles/v7/115
    Details on the hardware of Advanced LIGO: https://arxiv.org/pdf/1411.4547.pdf
    A similar analysis done by Pierce et. al.: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.121.061102

    See the full article here .

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    What is ParticleBites?

    ParticleBites is an online particle physics journal club written by graduate students and postdocs. Each post presents an interesting paper in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.

    The papers are accessible on the arXiv preprint server. Most of our posts are based on papers from hep-ph (high energy phenomenology) and hep-ex (high energy experiment).

    Why read ParticleBites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. With each brief ParticleBite, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in particle physics.

    Who writes ParticleBites?

    ParticleBites is written and edited by graduate students and postdocs working in high energy physics. Feel free to contact us if you’re interested in applying to write for ParticleBites.

    ParticleBites was founded in 2013 by Flip Tanedo following the Communicating Science (ComSciCon) 2013 workshop.

    2
    Flip Tanedo UCI Chancellor’s ADVANCE postdoctoral scholar in theoretical physics. As of July 2016, I will be an assistant professor of physics at the University of California, Riverside

    It is now organized and directed by Flip and Julia Gonski, with ongoing guidance from Nathan Sanders.

     
  • richardmitnick 3:45 pm on December 5, 2019 Permalink | Reply
    Tags: , , , , Gravitational wave astronomy, , , , , Quantum vacuum squeezer   

    From MIT News: “New instrument extends LIGO’s reach” 

    MIT News

    From MIT News

    December 5, 2019
    Jennifer Chu

    1
    Researchers install a new quantum squeezing device into one of LIGO’s gravitational wave detectors. Image: Lisa Barsotti

    2
    A close-up of the quantum squeezer which has expanded LIGO’s expected detection range by 50 percent. Image: Maggie Tse

    Just a year ago, the National Science Foundation-funded Laser Interferometer Gravitational-wave Observatory, or LIGO, was picking up whispers of gravitational waves every month or so. Now, a new addition to the system is enabling the instruments to detect these ripples in space-time nearly every week.

    Since the start of LIGO’s third operating run in April, a new instrument known as a quantum vacuum squeezer has helped scientists pick out dozens of gravitational wave signals, including one that appears to have been generated by a binary neutron star — the explosive merging of two neutron stars.

    The squeezer, as scientists call it, was designed, built, and integrated with LIGO’s detectors by MIT researchers, along with collaborators from Caltech and the Australian National University, who detail its workings in a paper published today in the journal Physical Review Letters.

    What the instrument “squeezes” is quantum noise — infinitesimally small fluctuations in the vacuum of space that make it into the detectors. The signals that LIGO detects are so tiny that these quantum, otherwise minor fluctuations can have a contaminating effect, potentially muddying or completely masking incoming signals of gravitational waves.

    “Where quantum mechanics comes in relates to the fact that LIGO’s laser is made of photons,” explains lead author Maggie Tse, a graduate student at MIT. “Instead of a continuous stream of laser light, if you look close enough it’s actually a noisy parade of individual photons, each under the influence of vacuum fluctuations. Whereas a continuous stream of light would create a constant hum in the detector, the individual photons each arrive at the detector with a little ‘pop.’”

    “This quantum noise is like a popcorn crackle in the background that creeps into our interferometer, and is very difficult to measure,” adds Nergis Mavalvala, the Marble Professor of Astrophysics and associate head of the Department of Physics at MIT.

    With the new squeezer technology, LIGO has shaved down this confounding quantum crackle, extending the detectors’ range by 15 percent. Combined with an increase in LIGO’s laser power, this means the detectors can pick out a gravitational wave generated by a source in the universe out to about 140 megaparsecs, or more than 400 million light years away. This extended range has enabled LIGO to detect gravitational waves on an almost weekly basis.

    “When the rate of detection goes up, not only do we understand more about the sources we know, because we have more to study, but our potential for discovering unknown things comes in,” says Mavalvala, a longtime member of the LIGO scientific team. “We’re casting a broader net.”

    The new paper’s lead authors are graduate students Maggie Tse and Haocun Yu, and Lisa Barsotti, a principal research scientist at MIT’s Kavli Institute for Astrophysics and Space Research, along with others in the LIGO Scientific Collaboration.

    Quantum limit

    LIGO comprises two identical detectors, one located at Hanford, Washington, and the other at Livingston, Louisiana. Each detector consists of two 4-kilometer-long tunnels, or arms, each extending out from the other in the shape of an “L.”

    MIT /Caltech Advanced aLigo

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    To detect a gravitational wave, scientists send a laser beam from the corner of the L-shaped detector, down each arm, at the end of which is suspended a mirror. Each laser bounces off its respective mirror and travels back down each arm to where it started. If a gravitational wave passes through the detector, it should shift one or both of the mirrors’ position, which would in turn affect the timing of each laser’s arrival back at its origin. This timing is something scientists can measure to identify a gravitational wave signal.

    The main source of uncertainty in LIGO’s measurements comes from quantum noise in a laser’s surrounding vacuum. While a vacuum is typically thought of as a nothingness, or emptiness in space, physicists understand it as a state in which subatomic particles (in this case, photons) are being constantly created and destroyed, appearing then disappearing so quickly they are extremely difficult to detect. Both the time of arrival (phase) and number (amplitude) of these photons are equally unknown, and equally uncertain, making it difficult for scientists to pick out gravitational-wave signals from the resulting background of quantum noise.

    And yet, this quantum crackle is constant, and as LIGO seeks to detect farther, fainter signals, this quantum noise has become more of a limiting factor.

    “The measurement we’re making is so sensitive that the quantum vacuum matters,” Barsotti notes.

    Putting the squeeze on “spooky” noise

    The research team at MIT began over 15 years ago to design a device to squeeze down the uncertainty in quantum noise, to reveal fainter and more distant gravitational wave signals that would otherwise be buried the quantum noise.

    Quantum squeezing was a theory that was first proposed in the 1980s, the general idea being that quantum vacuum noise can be represented as a sphere of uncertainty along two main axes: phase and amplitude. If this sphere were squeezed, like a stress ball, in a way that constricted the sphere along the amplitude axis, this would in effect shrink the uncertainty in the amplitude state of a vacuum (the squeezed part of the stress ball), while increasing the uncertainty in the phase state (stress ball’s displaced, distended portion). Since it is predominantly the phase uncertainty that contributes noise to LIGO, shrinking it could make the detector more sensitive to astrophysical signals.

    When the theory was first proposed nearly 40 years ago, a handful of research groups tried to build quantum squeezing instruments in the lab.

    “After these first demonstrations, it went quiet,” Mavalvala says.

    “The challenge with building squeezers is that the squeezed vacuum state is very fragile and delicate,” Tse adds. “Getting the squeezed ball, in one piece, from where it is generated to where it is measured is surprisingly hard. Any misstep, and the ball can bounce right back to its unsqueezed state.”

    Then, around 2002, just as LIGO’s detectors first started searching for gravitational waves, researchers at MIT began thinking about quantum squeezing as a way to reduce the noise that could possibly mask an incredibly faint gravitational wave signal. They developed a preliminary design for a vacuum squeezer, which they tested in 2010 at LIGO’s Hanford site. The result was encouraging: The instrument managed to boost LIGO’s signal-to-noise ratio — the strength of a promising signal versus the background noise.

    Since then, the team, led by Tse and Barsotti, has refined its design, and built and integrated squeezers into both LIGO detectors. The heart of the squeezer is an optical parametric oscillator, or OPO — a bowtie-shaped device that holds a small crystal within a configuration of mirrors. When the researchers direct a laser beam to the crystal, the crystal’s atoms facilitate interactions between the laser and the quantum vacuum in a way that rearranges their properties of phase versus amplitude, creating a new, “squeezed” vacuum that then continues down each of the detector’s arm as it normally would. This squeezed vacuum has smaller phase fluctuations than an ordinary vacuum, allowing scientists to better detect gravitational waves.

    In addition to increasing LIGO’s ability to detect gravitational waves, the new quantum squeezer may also help scientists better extract information about the sources that produce these waves.

    “We have this spooky quantum vacuum that we can manipulate without actually violating the laws of nature, and we can then make an improved measurement,” Mavalvala says. “It tells us that we can do an end-run around nature sometimes. Not always, but sometimes.”

    This research was supported, in part, by the National Science Foundation. LIGO was constructed by Caltech and MIT.

    See the full article here .


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  • richardmitnick 1:37 pm on October 4, 2019 Permalink | Reply
    Tags: , , , , , Gravitational wave astronomy, KAGRA joins the hunt,   

    From Caltech: “KAGRA to Join LIGO and Virgo in Hunt for Gravitational Waves” 

    Caltech Logo

    From Caltech

    October 04, 2019
    Whitney Clavin
    wclavin@caltech.edu

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

    Japan’s Kamioka Gravitational-wave Detector (KAGRA) will soon team up with the National Science Foundation’s Laser Interferometer Gravitational-wave Observatory (LIGO) and Europe’s Virgo in the search for subtle shakings of space and time known as gravitational waves. Representatives for the three observatories signed a memorandum of agreement (MOA) about their collaborative efforts today, October 4. The agreement includes plans for joint observations and data sharing.

    “This is a great example of international scientific cooperation,” says Caltech’s David Reitze, executive director of the LIGO Laboratory. “Having KAGRA join our network of gravitational-wave observatories will significantly enhance the science in the coming decade.”

    “At present, KAGRA is in the commissioning phase, after the completion of its detector construction this spring. We are looking forward to joining the network of gravitational-wave observations later this year,” says Takaaki Kajita, principal investigator of the KAGRA project and co-winner of the 2015 Nobel Prize in Physics.

    In 2015, the twin detectors of LIGO, one in Washington and the other in Louisiana, made history by making the first direct detection of gravitational waves, a discovery that earned three of the project’s founders—Caltech’s Barry Barish, Ronald and Maxine Linde Professor of Physics, Emeritus, and Kip Thorne, Richard P. Feynman Professor of Theoretical Physics, Emeritus; and MIT’s Rainer Weiss, professor of physics, emeritus—the 2017 Nobel Prize in Physics. Since then, LIGO and its partner Virgo have identified more than 30 likely detections of gravitational waves, mostly from colliding black holes.

    “The more detectors we have in the global gravitational-wave network, the more accurately we can localize the gravitational-wave signals on the sky, and the better we can determine the underlying nature of cataclysmic events that produced the signals.” says Reitze.

    For instance, in 2017, Virgo and the two LIGO detectors were able together to localize a merger of two neutron stars to a patch of sky about 30 square degrees in size, or less than 0.1 percent of the sky. This was a small enough patch to enable ground-based and space telescopes to pinpoint the galaxy that hosted the collision and observe its explosive aftermath in light.

    “These findings amounted to the first time a cosmic event had been observed in both gravitational waves and light and gave astronomers a first-of-its kind look at the spectacular smashup of neutron stars,” says Virgo Collaboration spokesperson Jo van den Brand of Nikhef (the Dutch National Institute for Subatomic Physics) and Maastricht University in the Netherlands.

    With KAGRA joining the network, these gravitational-wave events will eventually be narrowed down to patches of sky that are only about 10 square degrees, greatly enhancing the ability of light-based telescopes to carry out follow-up observations. For its initial run, KAGRA will operate at sensitivities that are likely too low to detect gravitational waves, but with time, as the performance of the instrumentation is improved, it will reach sensitivities high enough to join the hunt.

    Having a fourth detector will also increase the overall detection rate, helping scientists to probe and understand some of the most energetic events in the universe.

    KAGRA is expected to come online for the first time in December of this year, joining the third observing run of LIGO and Virgo, which began on April 1, 2019.

    MIT /Caltech Advanced aLigo


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    The Japanese detector will pioneer two new approaches to gravitational-wave searches. It will be the first kilometer-scale gravitational-wave observatory to operate underground, which will dampen unwanted noise from winds and seismic activity; and it will be the first to use cryogenically chilled mirrors, a technique that cuts down on thermal noise.

    “These features could supply a very important direction for the futureof gravitational-wave detectors with much higher sensitivities. Therefore, we should make every effort, for the global gravitational-wave community, to prove that the underground site and the cryogenic mirrors are useful,” says Kajita.

    The new MOA also includes the German-British GEO600 detector. Although GEO600 is not sensitive enough to detect gravitational-wave signals from distant black hole and neutron star collisions, it has been important for testing new technologies that will be key for improving future detectors. In addition, LIGO India is expected to join the network of observatories in 2025, signifying the beginning of a truly global effort to catch ripples in the fabric of space and time.

    Additional information about the gravitational-wave observatories:

    LIGO is funded by NSF and operated by Caltech and MIT, which conceived of LIGO and lead the project. 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. Approximately 1,300 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 is currently composed of approximately 480 scientists, engineers, and technicians from about 96 institutes from Belgium, France, Germany, Hungary, Italy, the Netherlands, Poland, and Spain. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy, and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and Nikhef in the Netherlands. A list of the Virgo Collaboration members 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.

    The KAGRA project is supported by MEXT (Ministry of Education, Culture, Sports, Science, and Technology-Japan). KAGRA is hosted by the Institute for Cosmic Ray Research (ICRR), the University of Tokyo, and co-hosted by High Energy Accelerator Research Organization (KEK) and the National Astronomical Observatory of Japan (NAOJ). The KAGRA collaboration is composed of more than 360 individuals from more than 100 institutions from 15 countries/regions. The list of collaborators’ affiliations is available at http://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA/KSC#KAGRAcollaborators. More information is available on the KAGRA website at https://gwcenter.icrr.u-tokyo.ac.jp/en/.

    See the full article here .


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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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  • richardmitnick 9:49 am on October 2, 2019 Permalink | Reply
    Tags: , , , Collision between a black hole and a neutron star?, , Gravitational wave astronomy, ,   

    From Symmetry: “Chasing gravitational waves” 

    Symmetry Mag
    From Symmetry<

    10/01/19
    Diana Kwon

    1
    A. Tonita, L. Rezzolla/Goethe University of Frankfurt​, &​ F. Pannarale/Sapienza University of Rome

    When LIGO and Virgo detected the echoes that likely came from a collision between a black hole and a neutron star, dozens of physicists began a hunt for the signal’s electromagnetic counterpart.

    Around mid-afternoon on August 14, a pulse passed simultaneously through the laser beams of three enormous gravitational-wave detectors, the twin locations of the Laser Interferometer Gravitational-Wave Observatory, or LIGO, in Louisiana and Washington, and the Virgo detector in Italy.

    MIT /Caltech Advanced aLigo


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Almost immediately, alerts beeped smartphones, tablets and laptops to life around the globe. Many of the physicists who saw this notification immediately dropped what they were doing and dashed to their computers to investigate.

    What they soon hoped to find was the first optical evidence that they were detecting a collision between a black hole and a neutron star.

    Scientists may have detected violent collision between neutron star, black hole

    An ear on the universe

    All objects with mass—including stars, planets and even humans—emit gravitational waves when they change speed or direction. But most gravitational waves are much too weak to detect. Even highly sensitive instruments like LIGO and Virgo, which are akin to microphones that hear signals from all directions, can only identify very “loud” gravitational waves caused by exceptionally massive objects that are accelerating rapidly.

    So far, the gravitational waves detected have all come from compact binaries, or two massive objects spiraling around and smashing into one another. There are three different types of pairings in a compact binary—two black holes, two neutron stars, or a neutron star and a black hole.

    Since black holes are more massive than neutron stars, their clashes generate the loudest gravitational waves. Because of this, they are the easiest to find. After their first two observing runs, the LIGO-Virgo collaboration announced official detections of 10 colliding black hole pairs.

    Neutron star-neutron star mergers, called kilonovae, are the quietest of the three. In October 2017, scientists announced the first observation of such a collision.

    It was the first successful use of LIGO-Virgo in multi-messenger astronomy, in which cosmological phenomena are examined through multiple types of signals, such as gravitational waves and electromagnetic sources like X-rays, radio waves and light.

    LIGO and Virgo send out an alert each time they hear an interesting signal to allow scientists at other observatories to immediately point their instruments at the spot in the sky where the signal most likely originated to collect as much data as possible about the source.

    The alert that went out after the neutron star merger mobilized scientists at telescopes around the world, including the DECam, a US Department of Energy-funded instrument mounted onto the National Science Foundation-funded 4-meter Blanco Telescope in Chile; the Very Large Array in New Mexico; and the Fermi Gamma-Ray Space Telescope orbiting our planet. Together, their observations helped provide evidence for a long-standing hypothesis that heavy elements such as gold and uranium were formed in the cosmic explosions that occur when two neutron stars crash.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


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

    Timeline of the Inflationary Universe WMAP

    The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

    According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

    DES is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

    Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

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

    NASA/Fermi LAT


    NASA/Fermi Gamma Ray Space Telescope

    “That event was unbelievably exciting and scientifically rich,” says Daniel Holz, an astrophysicist at the University of Chicago and a member of both LIGO and DES-GW. “The thrill of being part of that was incredible.”

    LIGO and Virgo have released dozens of public alerts about potential detections since the beginning of their third observing run this April. To date, these include potential observations of 20 binary black holes, 4 binary neutron stars, and 2 neutron star-black holes—but none of the these has been seen with a separate electromagnetic signal.

    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

    Masses in the Stellar Graveyard LIGO Virgo| Frank Elavsky | Northwestern

    The alerts are sent out almost immediately after the detectors pick up on a promising signal. In addition to identifying the potential candidate and its location on the sky, the notifications include a false alarm rate that portrays the likelihood that the proposed event was real. As researchers conduct further analyses on the data, the collaboration publishes updated estimates. If the signal turns out to be mere noise, they release a retraction.

    A needle in a haystack

    After the alert this August, the Slack channel for DES-GW, a group of scientists who use DECam to search for the optical counterparts of gravitational waves, was abuzz with chatter.

    At first, the gravitational wave was only classified as a “mass gap” detection, a signal from a pair of objects that was between the mass of the lightest black hole and the heaviest neutron star. This suggested the gravitational wave came from a new type of source, says Antonella Palmese, a postdoc at Fermilab and a member of DES-GW. But it could have been a merger between two unusually small black holes, in which case, it would be invisible to an instrument like DECam.

    After further analysis of the gravitational wave data, LIGO and Virgo scientists were able to categorize the signal as most likely a clash between a black hole and a neutron star. Although the collaboration hasn’t yet announced an official detection, their alert classified the event with greater than 99% confidence. It was their clearest gravitational-wave signal from a black hole-neutron star merger yet.

    “The moment when we got really excited and were all over our laptops was when we received the classification that it was a black hole-neutron star merger,” Palmese says. “In that case, you might expect the material from the neutron star to emit some electromagnetic counterpart that we can observe from our telescopes.”

    Once they received the classification, the group immediately got to work analyzing the information provided from the gravitational wave observatories and making plans to take data of their own with DECam as soon as possible. “We had to jump into action right away to try to do the observation,” says Marcelle Soares-Santos, an astrophysicist at Brandeis University who was at home when she received the first LIGO-Virgo message on her phone. “We managed to be on the sky in less than 24 hours.”

    According to the alert, the slice of sky that the signal could have originated from was tiny, providing astronomers with a clear target at which to point their instruments.

    “It was clear from the beginning that this event was special,” Soares-Santos says. “Several of us ended up staying up multiple nights because we were observing the same area of the sky multiple times.”

    Continuing the chase

    To identify optical counterparts of the source, DES-GW scientists look for transients: short-lived bursts of electromagnetic energy. Over the course of seven observing nights, DES-GW identified approximately 23 potential sources for the gravitational waves. Over the last few weeks, the group has been examining each of these to try to rule out the possibility that they are other celestial objects.

    One of the most common contaminants in these candidates are supernovae. Physicists can identify whether an object is a supernova by observing how long it takes to disappear. Unlike a black hole-neutron star merger, which would fade quickly, the aftermath of these stellar explosions usually remains in the sky for around a month or more.

    Finding the optical counterpart of the black hole-neutron star collision would be exciting for several reasons. First of all, this would be the first detection of such an event, so it could help reveal how such a process happens—whether the neutron star is ripped apart by a black hole or swallowed in one fell swoop. By observing this process, physicists could learn about the material that neutron stars are made of, which is the densest matter in the universe. These mergers may also help researchers better understand which elements are generated during this process.

    At this point, enough time has passed that it’s unlikely that DES-GW will identify the optical counterpart to the gravitational waves produced from this likely neutron star-black hole collision. Still, even without the detection, the data gathered at electromagnetic instruments can be helpful. For example, it suggests that instead of colliding, the neutron star may simply have been swallowed by the black hole instead, leaving no visible signs.

    More observations of neutron star-black hole mergers will be necessary to determine how, exactly, this process is happening. Scientists don’t yet know for sure when LIGO-Virgo will hear another gravitational wave coming from this type of event. But there are still several months to go during the current observing run, so physicists are anticipating another detection that will be worth pursuing.

    “This was the most exciting event this season so far,” Soares-Santos says. “But I wouldn’t bet it’s the last.”

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 9:24 am on September 17, 2019 Permalink | Reply
    Tags: , , , , , Gravitational wave astronomy, , Ringing black holes,   

    From Science News: “Gravitational waves from a ringing black hole support the no-hair theorem” 

    From Science News

    September 16, 2019
    Emily Conover

    General relativity suggests the spacetime oddities can be fully described by their mass and spin.

    1

    After two black holes collide and meld into one, the new black hole “rings” (illustrated), emitting gravitational waves before settling down into a quiet state. M. Isi/MIT, NASA

    For black holes, it’s tough to stand out from the crowd: Donning a mohawk is a no-no.

    Ripples in spacetime produced as two black holes merged into one suggest that the behemoths have no “hair,” scientists report in the Sept. 13 Physical Review Letters. That’s another way of saying that, as predicted by Einstein’s general theory of relativity, black holes have no distinguishing characteristics aside from mass and the rate at which they spin (SN: 9/24/10).

    “Black holes are very simple objects, in some sense,” says physicist Maximiliano Isi of MIT.

    Detected by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, in 2015, the spacetime ripples resulted from a fateful encounter between two black holes, which spiraled around each other before crashing together to form one big black hole (SN: 2/11/16).

    MIT /Caltech Advanced aLigo

    In the aftermath of that coalescence, the newly formed big black hole went through a period of “ringdown.” It oscillated over several milliseconds as it emitted gravitational waves, similar to the way a struck bell vibrates and makes sound waves before eventually quieting down.

    Reverberating black holes emit gravitational waves not at a single frequency, but with additional, short-lived frequencies known as overtones — much like a bell rings with multiple tones in addition to its main pitch.

    Measuring the ringing black hole’s main frequency as well as one overtone allowed the researchers to compare those waves with the prediction for a hairless black hole. The results agreed within 20 percent.

    That result still leaves some wiggle room for the no-hair theorem to be proved wrong. But, “It’s a clear demonstration that the method works,” says physicist Leo Stein of the University of Mississippi in Oxford, who was not involved with the research. “And hopefully the precision will increase as LIGO improves.”

    The researchers also calculated the mass and spin of the black hole, using only waves from the ringdown period. The figures agreed with the values estimated from the entire event — including the spiraling and merging of the original two black holes — and so reinforced the idea that the resulting black hole’s behavior was determined entirely by its mass and spin.

    But just as a mostly bald man may sport a few strands, black holes could reveal some hair on closer inspection. If they do, that might lead to a solution to the information paradox, a puzzle about what happens to information that falls into a black hole (SN: 5/16/14). For example, in a 2016 attempt to resolve the paradox, physicist Stephen Hawking and colleagues suggested that black holes might have “soft hair” (SN: 4/3/18).

    “It could still be that these objects have more mysteries to them that will only be revealed by future, more sensitive measurements,” Isi says.

    See the full article here .


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  • richardmitnick 9:40 am on August 31, 2019 Permalink | Reply
    Tags: "Scientists Detected 2 Black Hole Mergers Just 21 Mins Apart But It's Not What We Hoped", , , Gravitational wave astronomy, ,   

    From Science Alert and LIGO: “Scientists Detected 2 Black Hole Mergers Just 21 Mins Apart, But It’s Not What We Hoped” 

    ScienceAlert

    From Science Alert

    MIT /Caltech Advanced aLigo

    31 AUG 2019
    MIKE MCRAE

    1
    (Des Green/iStock)

    Last Wednesday, a gravitational wave detection gave astronomers quite the surprise. As researchers were going about their work at the Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of gravitational waves rolled in just minutes apart.

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    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

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

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    The first, labelled S190828j, was picked up by all three of LIGO’s gravitational wave detectors at 06:34 am, coordinated universal time.

    MIT /Caltech Advanced aLigo


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    The second, S190828l, was measured at 06:55 – a mere 21 minutes later.

    Both seemed to be the run-of-the-mill dying screams of black holes as they squish together. But here’s why it’s so surprising: astronomers wouldn’t expect to see a pair of signals in such quick succession.

    In fact, this is only the second time two detections have rolled in on the same day. What’s more, at first glance they also seemed to echo from more or less the same patch of sky.

    “This is a genuine “Uh, wait, what?; We’ve never seen that before…” moment in gravitational wave astronomy,” astrophysicist Robert Routledge from McGill University later tweeted, after openly speculating that it mightn’t be a mere coincidence.

    Non-scientists — this is a genuine “Uh, wait, what? We’ve never seen that before…….” moment in gravitational wave astronomy. If you’d like to see how double-checks and confirmations and conclusions occur – pay attention, in real time. Happening now.
    — Robert Rutledge (@rerutled) August 28, 2019

    Nobody can blame Routledge for getting excited. Unexpected events like this are what discoveries are made of, after all. As he said, this is science in real time.

    One possibility briefly kicked around was that S190828j and S190828l were actually the same wave, divided by some sort of distortion in space before being roughly thrown together again. This would have been huge.

    Gravitational lensing – the warping effect an intervening mass has on space, as described by general relativity – can divide and duplicate the rays of light from far-off objects. It has become a useful tool for astronomers in the measurement of distances.

    Gravitational Lensing NASA/ESA

    If this had indeed been a two-for-one deal, it would be the first time a gravitational wave had been observed through a gravitational lens.

    Alas, it’s now looking pretty unlikely. As the hours passed, new details emerged indicating the two signals don’t overlap enough to be originating from the same source.

    If this were a lensing event, you’d expect the two localizations to sit more or less right on top of each other. They have similar shapes and appear in the same part of the sky, but they don’t really overlap: pic.twitter.com/lqvigNhyBl
    — Robert McNees (@mcnees) August 28, 2019

    So close, and yet so far. Right now, this twin event is looking more like a coincidence.

    To look on the bright side, we now live in an age where the detection of the crash-boom of galactic giants isn’t a rare event, but rather an endless peel of thunder we can record and measure with an insane level of accuracy. It’s hard to believe the first collision was detected only a few years ago.

    Scientists face a problem in the wake of freaky events like this one. On the one hand, wild speculations have a habit of taking on a life of their own when discussed so frankly in a public space, transforming into an established fact while barely half baked.

    But time can be of the essence when we’re scanning a near-infinite amount of sky for clues, too. By throwing ideas out broadly, different groups of researchers can turn their attention to a phenomenon and collect data while it’s still hot.

    This is what scientists do best – stumble across odd events, throw out ideas, and debate which ones deserve to be inspected and which should be abandoned.

    If there’s more to S190828j and S190828l than meets the eye, we’ll let you know. For now, we can be disappointed that there was no Earth-shaking discovery, while still being amazed that we have the technology to discover it at all.

    We really ought to celebrate the ‘disappointments’ a little more often.

    See the full article here .


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  • richardmitnick 8:44 am on August 16, 2019 Permalink | Reply
    Tags: "Early Reports Indicate We May Have Detected a Black Hole And Neutron Star Collision", , , , , Gravitational wave astronomy, If it really is a collision between a neutron star and a black hole it will be the first time such a binary system has ever been seen., , Merger event S190814bv,   

    From Science Alert: “Early Reports Indicate We May Have Detected a Black Hole And Neutron Star Collision” 

    ScienceAlert

    From Science Alert

    1
    This distant galaxy is the target of our telescopes. (UCSC Transients)

    It looks like we’ve bagged another win for gravitational wave astronomy. A new gravitational wave detection is the best candidate yet for a type of cosmic collision never seen – the elusive merger between a black hole and a neutron star.

    The event, called S190814bv, was detected by the LIGO and Virgo interferometers at 11 minutes past 9 pm UTC on 14 August. And, based on initial analysis, there’s a 99 percent chance that it’s a neutron star-black hole kaboom.

    MIT /Caltech Advanced aLigo


    Advanced Virgo

    Even as you read this, scientists are poring over data and staring hard at the sky, looking for the light that may have been left behind by the neutron star as it is absorbed into the black hole.

    “It’s like the night before Christmas,” astronomer Ryan Foley of the University of California, Santa Cruz told ScienceAlert. “I’m just waiting to see what’s under the tree.”

    Since that amazing first gravitational wave detection – a collision between two stellar mass black holes – was announced in February 2016, the field has been only growing stronger. The technology is so sophisticated it can detect collisions between two neutron stars – objects much less massive than black holes.

    Both neutron stars and black holes are the ultradense remains of a dead star, but we’ve never seen a black hole smaller than 5 times the mass of the Sun, or a neutron star larger than around 2.5 times the mass of the Sun.

    But a collision between a black hole and a neutron star has evaded us. One detection looked like it might have been such an event, earlier this year, but the odds were just 13 percent. And the signal to noise ratio was so low, astronomers didn’t follow it up.

    That’s not the case with S190814bv. The signal is really strong, and astronomers are excited – if it really is a collision between a neutron star and a black hole, it will be the first time such a binary system has ever been seen.

    This would mean that such binary systems, hypothetical until now, are indeed possible. We could even get clues as to their formation – did they form as a binary, living, growing and dying together? Or did the black hole capture a passing neutron star into its orbit?

    Believe it or not, we can learn that from the gravitational wave signal – ripples in spacetime caused by a massive collision, like a rock dropped in a pond – if it’s strong enough. Clues to the formation of the binary are encoded in the waveform, along with the masses of the individual objects, their velocity and acceleration.

    “From the gravitational wave signal, one can get information about the spins of the individual objects and their orientation compared with the axis to the orbit,” physicist Peter Veitch from the University of Adelaide in Australia and OzGrav (the Australian branch of the LIGO Scientific Collaboration) told ScienceAlert.

    “[We’re] looking to see whether the rotational spin of the individual objects are aligned with each other, which might suggest that they were initially in a binary system. Whereas if one compact object was captured by another as galaxies merged, for example, then you might expect these objects have different spins pointing in different directions.”

    Foley and his colleagues are currently using the Keck Observatory to study a galaxy around 900 million light-years away.

    Keck Observatory, operated by Caltech and the University of California, Maunakea Hawaii USA, 4,207 m (13,802 ft)

    That’s where they think the signal might have originated. They’re looking for electromagnetic radiation that might result from the collision involving a neutron star.

    And, of course, there’s the burning question: what do neutron star guts look like?

    “We would love to observe a black hole ripping a neutron star apart as they come together,” says theoretical physicist Susan Scott of the Australian National University and OzGrav.

    “This would give us vital information about the material which makes up the densest stars in the Universe – neutron stars – which remains a very big open question in the field.”

    If there’s no electromagnetic radiation detected, that could mean astronomers are simply looking in the wrong place. Or it could mean that the electromagnetic radiation is too weak to be detected.

    It could also mean a neutron star isn’t involved – which would be very interesting, because the signal suggests that the smaller object is less than three times the mass of the Sun. If it’s not a neutron star, it might instead be the smallest black hole we’ve ever detected.

    Or it could mean that the dynamics between a neutron star and a black hole as they smoosh together into a slightly bigger black hole are even weirder than we knew.

    “My favourite way to think about it (for the moment) is that if a black hole is much more massive than a neutron star, then when they merge, the neutron star will be torn apart inside the event horizon of the black hole! In that case, even if there’s plenty of light generated, none will escape the black hole for us to see,” Foley told ScienceAlert.

    “That is about as close to science fiction as you get.”

    See the full article here .


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  • richardmitnick 7:13 am on July 21, 2019 Permalink | Reply
    Tags: "Where Do Supermassive Black Holes Come From?", , , , , , Gravitational wave astronomy, , , ,   

    From Western University, CA and WIRED: “Where Do Supermassive Black Holes Come From?” 

    From Western University Canada

    2
    Scott Woods, Western University, Illustration of supermassive black hole
    via

    WIRED

    Wired logo
    NASA

    June 28, 2019

    Researchers decipher the history of supermassive black holes in the early universe.

    At Western University
    MEDIA CONTACT:
    Jeff Renaud, Senior Media Relations Officer,
    519-661-2111, ext. 85165,
    519-520-7281 (mobile),
    jrenaud9@uwo.ca, @jeffrenaud99

    07.18.19
    From Wired
    Meredith Fore

    1
    NASA

    A pair of researchers at Western University in Ontario, Canada, developed their model by looking at quasars, which are supermassive black holes.

    Astronomers have a pretty good idea of how most black holes form: A massive star dies, and after it goes supernova, the remaining mass (if there’s enough of it) collapses under the force of its own gravity, leaving behind a black hole that’s between five and 50 times the mass of our Sun. What this tidy origin story fails to explain is where supermassive black holes, which range from 100,000 to tens of billions of times the mass of the Sun, come from. These monsters exist at the center of almost all galaxies in the universe, and some emerged only 690 million years after the Big Bang. In cosmic terms, that’s practically the blink of an eye—not nearly long enough for a star to be born, collapse into a black hole, and eat enough mass to become supermassive.

    One long-standing explanation for this mystery, known as the direct-collapse theory, hypothesizes that ancient black holes somehow got big without the benefit of a supernova stage. Now a pair of researchers at Western University in Ontario, Canada—Shantanu Basu and Arpan Das—have found some of the first solid observational evidence for the theory. As they described late last month in The Astrophysical Journal Letters, they did it by looking at quasars.

    Quasars are supermassive black holes that continuously suck in, or accrete, large amounts of matter; they get a special name because the stuff falling into them emits bright radiation, making them easier to observe than many other kinds of black holes. The distribution of their masses—how many are bigger, how many are smaller, and how many are in between—is the main indicator of how they formed.

    Astrophysicists at Western University have found evidence for the direct formation of black holes that do not need to emerge from a star remnant. The production of black holes in the early universe, formed in this manner, may provide scientists with an explanation for the presence of extremely massive black holes at a very early stage in the history of our universe.

    After analyzing that information, Basu and Das proposed that the supermassive black holes might have arisen from a chain reaction. They can’t say exactly where the seeds of the black holes came from in the first place, but they think they know what happened next. Each time one of the nascent black holes accreted matter, it would radiate energy, which would heat up neighboring gas clouds. A hot gas cloud collapses more easily than a cold one; with each big meal, the black hole would emit more energy, heating up other gas clouds, and so on. This fits the conclusions of several other astronomers, who believe that the population of supermassive black holes increased at an exponential rate in the universe’s infancy.

    “This is indirect observational evidence that black holes originate from direct-collapses and not from stellar remnants,” says Basu, an astronomy professor at Western who is internationally recognized as an expert in the early stages of star formation and protoplanetary disk evolution.

    Basu and Das developed the new mathematical model by calculating the mass function of supermassive black holes that form over a limited time period and undergo a rapid exponential growth of mass. The mass growth can be regulated by the Eddington limit that is set by a balance of radiation and gravitation forces or can even exceed it by a modest factor.

    “Supermassive black holes only had a short time period where they were able to grow fast and then at some point, because of all the radiation in the universe created by other black holes and stars, their production came to a halt,” explains Basu. “That’s the direct-collapse scenario.”

    But at some point, the chain reaction stopped. As more and more black holes—and stars and galaxies—were born and started radiating energy and light, the gas clouds evaporated. “The overall radiation field in the universe becomes too strong to allow such large amounts of gas to collapse directly,” Basu says. “And so the whole process comes to an end.” He and Das estimate that the chain reaction lasted about 150 million years.

    The generally accepted speed limit for black hole growth is called the Eddington rate, a balance between the outward force of radiation and the inward force of gravity. This speed limit can theoretically be exceeded if the matter is collapsing fast enough; the Basu and Das model suggests black holes were accreting matter at three times the Eddington rate for as long as the chain reaction was happening. For astronomers regularly dealing with numbers in the millions, billions, and trillions, three is quite modest.

    “If the numbers had turned out crazy, like you need 100 times the Eddington accretion rate, or the production period is 2 billion years, or 10 years,” Basu says, “then we’d probably have to conclude that the model is wrong.”

    There are many other theories for how direct-collapse black holes could be created: Perhaps halos of dark matter formed ultramassive quasi-stars that then collapsed, or dense clusters of regular mass stars merged and then collapsed.

    For Basu and Das, one strength of their model is that it doesn’t depend on how the giant seeds were created. “It’s not dependent on some person’s very specific scenario, specific chain of events happening in a certain way,” Basu says. “All this requires is that some very massive black holes did form in the early universe, and they formed in a chain reaction process, and it only lasted a brief time.”

    The ability to see a supermassive black hole forming is still out of reach; existing telescopes can’t look that far back yet. But that may change in the next decade as powerful new tools come online, including the James Webb Space Telescope, the Wide Field Infrared Survey Telescope, and the Laser Interferometer Space Antenna—all of which will hover in low Earth orbit—as well as the Large Synoptic Survey Telescope, based in Chile.

    NASA/ESA/CSA Webb Telescope annotated

    NASA/WFIRST

    Gravity is talking. Lisa will listen. Dialogos of Eide

    ESA/LISA Pathfinder

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

    LSST Camera, built at SLAC

    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    In the next five or 10 years, Basu adds, as the “mountain of data” comes in, models like his and his colleague’s will help astronomers interpret what they see.

    Avi Loeb, one of the pioneers of direct-collapse black hole theory and the director of the Black Hole Initiative at Harvard, is especially excited for the Laser Interferometer Space Antenna. Set to launch in the 2030s, it will allow scientists to measure gravitational waves—fine ripples in the fabric of space-time—more accurately than ever before.

    “We have already started the era of gravitational wave astronomy with stellar-mass black holes,” he says, referring to the black hole mergers detected by the ground-based Laser Interferometer Gravitational-Wave Observatory.

    Its space-based counterpart, Loeb anticipates, could provide a better “census” of the supermassive black hole population.

    For Basu, the question of how supermassive black holes are created is “one of the big chinks in the armor” of our current understanding of the universe. The new model “is a way of making everything work according to current observations,” he says. But Das remains open to any surprises delivered by the spate of new detectors—since surprises, after all, are often how science progresses.

    MIT /Caltech Advanced aLigo



    VIRGO Gravitational Wave interferometer, near Pisa, Italy


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    LSC LIGO Scientific Collaboration


    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)

    See the full WIRED article here .
    See the full Western University article here .

    The University of Western Ontario (UWO), corporately branded as Western University as of 2012 and commonly shortened to Western, is a public research university in London, Ontario, Canada. The main campus is on 455 hectares (1,120 acres) of land, surrounded by residential neighbourhoods and the Thames River bisecting the campus’s eastern portion. The university operates twelve academic faculties and schools. It is a member of the U15, a group of research-intensive universities in Canada.

    The university was founded on 7 March 1878 by Bishop Isaac Hellmuth of the Anglican Diocese of Huron as the Western University of London, Ontario. It incorporated Huron University College, which had been founded in 1863. The first four faculties were Arts, Divinity, Law and Medicine. The Western University of London became non-denominational in 1908. Beginning in 1919, the university has affiliated with several denominational colleges. The university grew substantially in the post-World War II era, as a number of faculties and schools were added to university.

    Western is a co-educational university, with more than 24,000 students, and with over 306,000 living alumni worldwide. Notable alumni include government officials, academics, business leaders, Nobel Laureates, Rhodes Scholars, and distinguished fellows. Western’s varsity teams, known as the Western Mustangs, compete in the Ontario University Athletics conference of U Sports.

    Wired logo

    WIRED

    See the full article here .

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