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  • richardmitnick 12:57 pm on May 25, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT Advanced aLigo, , , N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey, , , NGC 6946 Fireworks Galaxy, SN 2017eaw   

    From Hubble: “Collapsing Star Gives Birth to a Black Hole” 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope

    NASA/ESA Hubble Telescope

    May 25, 2017
    Christopher Kochanek / Krzysztof Stanek
    Ohio State University, Columbus, Ohio
    614-292-5954 / 614-292-3433
    kochanek.1@osu.edu / stanek.32@osu.edu

    Scott Adams
    Caltech, Pasadena, California
    626-395-8676
    smadams@caltech.edu

    Pam Frost Gorder
    Ohio State University, Columbus, Ohio
    614-292-9475
    gorder.1@osu.edu

    Elizabeth Landau
    Jet Propulsion Laboratory, Pasadena, California
    818-354-6425
    elizabeth.r.landau@jpl.nasa.gov

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4514
    villard@stsci.edu

    1
    Massive Dying Star Goes Out With a Whimper Instead of a Bang

    Every second a star somewhere out in the universe explodes as a supernova. But some super-massive stars go out with a whimper instead of a bang. When they do, they can collapse under the crushing tug of gravity and vanish out of sight, only to leave behind a black hole. The doomed star, named N6946-BH1, was 25 times as massive as our sun. It began to brighten weakly in 2009. But, by 2015, it appeared to have winked out of existence. By a careful process of elimination, based on observations by the Large Binocular Telescope and the Hubble and Spitzer space telescopes, the researchers eventually concluded that the star must have become a black hole. This may be the fate for extremely massive stars in the universe.

    U Arizona Large Binocular Telescope, Mount Graham, Arizona, USA

    Astronomers have watched as a massive, dying star was likely reborn as a black hole. It took the combined power of the Large Binocular Telescope (LBT), and NASA’s Hubble and Spitzer space telescopes to go looking for remnants of the vanquished star, only to find that it disappeared out of sight.

    NASA/Spitzer Telescope

    It went out with a whimper instead of a bang.

    The star, which was 25 times as massive as our sun, should have exploded in a very bright supernova. Instead, it fizzled out—and then left behind a black hole.

    “Massive fails” like this one in a nearby galaxy could explain why astronomers rarely see supernovae from the most massive stars, said Christopher Kochanek, professor of astronomy at The Ohio State University and the Ohio Eminent Scholar in Observational Cosmology.

    As many as 30 percent of such stars, it seems, may quietly collapse into black holes — no supernova required.

    “The typical view is that a star can form a black hole only after it goes supernova,” Kochanek explained. “If a star can fall short of a supernova and still make a black hole, that would help to explain why we don’t see supernovae from the most massive stars.”

    He leads a team of astronomers who published their latest results in the Monthly Notices of the Royal Astronomical Society.

    Among the galaxies they’ve been watching is NGC 6946, a spiral galaxy 22 million light-years away that is nicknamed the “Fireworks Galaxy” because supernovae frequently happen there — indeed, SN 2017eaw, discovered on May 14th, is shining near maximum brightness now. Starting in 2009, one particular star, named N6946-BH1, began to brighten weakly. By 2015, it appeared to have winked out of existence.

    After the LBT survey for failed supernovas turned up the star, astronomers aimed the Hubble and Spitzer space telescopes to see if it was still there but merely dimmed. They also used Spitzer to search for any infrared radiation emanating from the spot. That would have been a sign that the star was still present, but perhaps just hidden behind a dust cloud.

    All the tests came up negative. The star was no longer there. By a careful process of elimination, the researchers eventually concluded that the star must have become a black hole.

    It’s too early in the project to know for sure how often stars experience massive fails, but Scott Adams, a former Ohio State student who recently earned his Ph.D. doing this work, was able to make a preliminary estimate.

    “N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we’ve been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae,” he said.

    “This is just the fraction that would explain the very problem that motivated us to start the survey, that is, that there are fewer observed supernovae than should be occurring if all massive stars die that way.”

    To study co-author Krzysztof Stanek, the really interesting part of the discovery is the implications it holds for the origins of very massive black holes — the kind that the LIGO experiment detected via gravitational waves. (LIGO is the Laser Interferometer Gravitational-Wave Observatory.)


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    It doesn’t necessarily make sense, said Stanek, professor of astronomy at Ohio State, that a massive star could undergo a supernova — a process which entails blowing off much of its outer layers — and still have enough mass left over to form a massive black hole on the scale of those that LIGO detected.

    “I suspect it’s much easier to make a very massive black hole if there is no supernova,” he concluded.

    Adams is now an astrophysicist at Caltech. Other co-authors were Ohio State doctoral student Jill Gerke and University of Oklahoma astronomer Xinyu Dai. Their research was supported by the National Science Foundation.

    NASA’s Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington, D.C. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena, California. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

    The Large Binocular Telescope is an international collaboration among institutions in the United Sates, Italy and Germany.

    See the full article here .
    See the JPL-Caltech full article here .

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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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    NASA image

     
  • richardmitnick 10:51 am on May 22, 2017 Permalink | Reply
    Tags: Caltech/MIT Advanced aLigo, Hubble detects a supermassive black hole ejected from the galactic core,   

    From Manu Garcia: “Hubble detects a supermassive black hole ejected from the galactic core” 


    Manu Garcia, a friend from IAC.

    The universe around us.
    Astronomy, everything you wanted to know about our local universe and never dared to ask.

    22/5/17
    Manu Garcia

    1
    The picture:
    The galaxy 3C186 , located about 8 billion light years from Earth is most likely the result of a merger of two galaxies. This is supported by the tidal tails arcuate generally produced by a gravitational pull between two colliding galaxies, identified by scientists. Merging galaxies also led to a fusion of the two supermassive black holes at their centers and the resulting black hole was expelled from its parent galaxy by gravitational waves created by the merger. The bright quasar, like a star, you can see in the center of the image. His previous host galaxy is the faint object, extended behind him. Photo credit: NASA, ESA, M. Chiaberge (STScI / ESA)

    An international team of astronomers using the Hubble Space Telescope has discovered a supermassive black hole that has been driven out of the center of the distant galaxy 3C186 .

    NASA/ESA Hubble Telescope

    The black hole was probably driven by the power of gravitational waves. This is the first time astronomers have found a supermassive black hole at such a great distance from its host galaxy ‘s center.

    Although other fugitives suspected black holes have been seen elsewhere, so far none has been confirmed. Now astronomers using the Hubble Space Telescope , NASA / ESA have detected a supermassive black hole with a mass a billion times the Sun, being expelled from its parent galaxy. ” We estimate that took the energy equivalent of 100 million supernovas exploding simultaneously to get rid of the black hole” describes Stefano Bianchi, co-author of the study, the Roma Tre University, Italy.

    Images taken by Hubble provided the first clue that the galaxy called 3C186 , was unusual. The images of the galaxy, located to 8 billion light years away, revealed a bright quasar, the energy signature of an active black hole located far from the galactic core. “Black holes reside at the centers of galaxies, so it is rare to see a quasar that is not in the center of the galaxy , ” says the team leader, Marco Chiaberge researcher ESA-AURA at the Institute of Sciences Space telescope, United States .

    The team calculated that the black hole has already traveled about 35,000 light years from the center of the host galaxy, it is more than the distance between the Sun and the center of the Milky Way. He continues his flight at a speed of 7.5 million kilometers per hour [1]. At this speed the black hole could travel from Earth to the moon in three minutes.

    Although we can not exclude other scenarios to explain the observations, the most plausible source of propulsive power is that this massive black hole was kicked gravity wave [2] triggered by the fusion of two massive black holes at the center of its host galaxy. This theory is supported by tidal tails arcuate identified by scientists, produced by a gravitational pull between two colliding galaxies.

    According to the theory presented by scientists, it is estimated that 2 billion years ago between 1 or two galaxies each with a central supermassive black hole merged. Black holes turned around each other in the center of the newly formed elliptical galaxy, creating gravitational waves that were dropped as water a lawn sprinkler [3]. As the two black holes did not have the same mass and rotational speed, gravitational waves emitted most strongly along one direction. When two black holes eventually merged, the anisotropic emission of gravitational waves generated kick that fired the resulting black hole outside the galactic center.

    “If our theory is correct, the observations provide strong evidence that supermassive black holes can merge,” says Stefano Bianchi on the importance of the discovery. “There is already evidence of black hole collisions for black holes of stellar mass, but the process that regulates supermassive black holes is more complex and still not fully understood.”

    Researchers are lucky enough to have captured this unique event because not all mergers of black holes produce gravitational waves unbalanced propelling a black hole outside the galaxy. The computer now want to secure a longer observation time with the Hubble , in combination with the Atacama Large Millimeter / submillimeter Array (ALMA) and other facilities, to more accurately measure the speed of the black hole and its disk surrounding gas within the nature of this rare object.

    notes:
    [1] As the black hole can not be observed directly, the mass and velocity of supermassive black holes were determined through spectroscopic analysis of its surrounding gas.

    [2] first predicted by Albert Einstein , gravitational waves are ripples in space which are created by the acceleration of massive objects. The corrugations are similar to concentric circles produced when a rock is thrown in a pond. In 2016, the Gravitational Wave Observatory ( LIGO ) helped astronomers to prove that there are detecting gravitational waves emanating from the merger of two black holes of stellar mass, which are several times more massive than the sun.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    [3] The black holes approach with time as radiating gravitational energy.

    See the full article here .

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  • richardmitnick 9:26 am on May 21, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT Advanced aLigo, , ,   

    From Manu Garcia: ” LIGO, Boxing Day” 


    Manu Garcia, a friend from IAC.

    The universe around us.
    Astronomy, everything you wanted to know about our local universe and never dared to ask.

    Author: Manu Astrologus – Update: 21/5/17
    Second detection of gravitational waves.

    1
    Artist illustration represents two binary black hole systems for molten GW150914 (left) and GW151226 (right). Pair of black holes are shown together in this illustration but actually detected at different times and in different parts of the sky. The images have been scaled to show the difference in the masses of black holes. In the event GW150914 , black holes were 29 and 36 times the mass of the sun, while GW151226 , the two black holes weighing between 14 and 8 solar masses. Image Credit: LIGO / A. Simonnet.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    The two gravitational wave detectors LIGO Hanford Washington and Livingston Louisiana have captured a second robust signal of two black holes in their final orbits then coalescence, fusion <>, in a single black hole. This event, called GW151226 , was seen on 26 December at 3:38:53 (coordinated universal time, also known as Greenwich Mean Time) near the end of the first LIGO observation period ( “O1”), and it was immediately nicknamed “the boxing day event”.

    As the first detection LIGO , this event was identified few minutes after passage of the gravitational wave. Subsequently, careful studies of tools and environments around the observatories showed that observed in the two detectors signal was truly distant black holes, about 1,400 million light years away, coinciding with the same distance as the first detected signal. However, the Boxing Day event differed from the first observation of gravitational waves LIGO in some important ways.

    The gravitational wave detectors came to the two almost simultaneously, indicating that the source is somewhere in heaven ring halfway between the two detectors. Knowing our pattern detector sensitivity, we can add that was a little more likely overhead or underfoot instead of west or east. With only two detectors, however, we can not reduce it much more than that. This differs from the first detected signal LIGO ( GW150914 , from 14 September 2015), which came from the southeast, hitting the detector Louisiana before Washington.
    The two black holes merged in the event of Boxing Day were less massive (14 and 8 times the mass of our sun) than those observed in the first detection GW150914 (36 and 29 times the mass of our sun). While this made the weakest signal that GW150914 , when these lighter black holes were combined, changed its signal at higher frequencies that bring in the sensitive band LIGO before the fusion event observed in September. This allowed us to observe more orbits that the first detection-orbits about 27 in about one second (this compares with only two tenths of observation in the first detection). Combined, these two factors (smaller and observed masses orbits) were keys to allow LIGO detect a weaker signal. They also allowed us to make more accurate comparisons with General Relativity. Note: the signal again coincides with Einstein’s theory.
    Last but not least, the event Boxing Day revealed that one of the first black holes was spinning like a top – and this is a first opportunity for LIGO can state this with confidence. A rotating black hole suggests that this object has a different story – p. Maybe “he sucked” the mass of a companion star before or after a star collapsing to form a black hole, achieving rotated in the process.

    With these two detections confirmed, along with a third probable detection made in October 2015 (believed to also could be caused by a pair of coalescing black holes) we can now begin to estimate the rate of coalescence of black hole in the universe based not in theory, but in actual observations. Of course, with only a few signs, our estimate is large uncertainties, but maybe now is between 9 and 240 binary coalescence of black hole Gigaparsec cubic per year, or about one every 10 years in a volume a trillion times the volume galaxy of the Milky Way. Happily, in its first months of operation, they advanced LIGO detectors were sensitive enough to dig deep enough into space to see about an event every two months.

    Our next observation interval – Watching Round # 2, or “O2” – will begin in the fall of 2016. With improved sensitivity, we expect to see more coalescence of black holes and possibly detect gravitational waves from other sources, such as mergers of binary star neutrons. We also expect the Virgo detector will join us later in the race O2. Virgo will be enormously useful for locating sources in the sky, collapsing the ring until a patch, but also helping us to understand the sources of gravitational waves.

    LIGO releases its data to the public. This policy of open data allows others to analyze our data, ensuring that LIGO and Virgo collaborations do not lose anything in their analyzes, and hoping that others might be even more interesting events. Our data are shared in the Open LIGO Science Center. GW151226 has its own page there.

    We invite you to stroll the LIGO Laboratory website where you will find charts to help you understand the observation of Boxing Day, links to the press release and suggestions for scientific papers if you want to deepen further. There you will also find links to the website of LIGO Scientific Collaboration, and our collaboration sister, Virgo, which are essential for these scientific results.

    Credit:
    LIGO.

    See the full article here .

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  • richardmitnick 12:49 pm on May 19, 2017 Permalink | Reply
    Tags: , , Caltech/MIT Advanced aLigo, , ESA/Lisa, GEO600, , ,   

    From Science Alert: “Einstein’s ‘Spooky’ Entanglement Is Guiding Next-Gen Gravitational Wave Detectors” 

    ScienceAlert

    Science Alert

    19 MAY 2017
    DAVID BLAIR

    1
    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    Breaking the standard quantum limit.

    The first direct detection of gravitational waves, a phenomenon predicted by Einstein’s 1915 general theory of relativity, was reported by scientists in 2016.

    Armed with this “discovery of the century”, physicists around the world have been planning new and better detectors of gravitational waves.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    Physicist Professor Chunnong Zhao and his recent PhD students Haixing Miao and Yiqiu Ma are members of an international team that has created a particularly exciting new design for gravitational wave detectors.

    The new design is a real breakthrough because it can measure signals below a limit that was previously believed to be an insurmountable barrier. Physicists call this limit the standard quantum limit. It is set by the quantum uncertainty principle.

    Proposal for gravitational-wave detection beyond the standard quantum limit through EPR entanglement
    Yiqiu Ma, Haixing Miao, Belinda Heyun Pang, Matthew Evans, Chunnong Zhao, Jan Harms, Roman Schnabel & Yanbei Chen

    The new design, published in Nature Physics this week, shows that this may not be a barrier any longer.

    Abstract

    In continuously monitored systems the standard quantum limit is given by the trade-off between shot noise and back-action noise. In gravitational-wave detectors, such as Advanced LIGO, both contributions can be simultaneously squeezed in a broad frequency band by injecting a spectrum of squeezed vacuum states with a frequency-dependent squeeze angle. This approach requires setting up an additional long baseline, low-loss filter cavity in a vacuum system at the detector’s site. Here, we show that the need for such a filter cavity can be eliminated, by exploiting Einstein–Podolsky–Rosen (EPR)-entangled signals and idler beams. By harnessing their mutual quantum correlations and the difference in the way each beam propagates in the interferometer, we can engineer the input signal beam to have the appropriate frequency-dependent conditional squeezing once the out-going idler beam is detected. Our proposal is appropriate for all future gravitational-wave detectors for achieving sensitivities beyond the standard quantum limit.
    6
    Figure 1
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    figure 2
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    Figure 3
    3
    Figure 4
    5
    Figure 5

    Using this and other new approaches may allow scientists to monitor black hole collisions and ‘spacequakes‘ across the whole of the visible Universe.

    4
    During a spacequake, Earth’s magnetic field shakes in a way that is analogous to the shaking of the ground during an earthquake. Image credit: Evgeny Panov, Space Research Institute of Austria.

    How gravitational wave detectors work

    Gravitational waves are not vibrations travelling through space, but rather vibrations of space itself.

    They have already told us about an unexpectedly large population of black holes. We hope that further study of gravitational waves will help us to better understand our Universe.

    But the technologies of gravitational wave detectors are likely to have enormous significance beyond this aspect of science, because in themselves they are teaching us how to measure unbelievably tiny amounts of energy.

    Gravitational wave detectors use laser light to pick up tiny vibrations of space created when black holes collide. The collisions create vast gravitational explosions.

    They are the biggest explosions known in the Universe, converting mass directly into vibrations of pure space.

    It takes huge amounts of energy to make space bend and ripple.

    Our detectors – exquisitely perfect devices that use big heavy mirrors with scarily powerful lasers – must measure space stretching by a mere billionth of a billionth of a metre over the four kilometre scale of our detectors. [LIGO, above.]

    These measurements already represent the smallest amount of energy ever measured.

    But for gravitational wave astronomers this is not good enough. They need even more sensitivity to be able to hear many more predicted gravitational ‘sounds’, including the sound of the moment the Universe was created in the big bang.

    This is where the new design comes in.

    A spooky idea from Einstein

    The novel concept is founded on original work from Albert Einstein.

    In 1935 Albert Einstein and co-workers Boris Podolsky and Nathan Rosen tried to depose the theory of quantum mechanics by showing that it predicted absurd correlations between widely spaced particles.

    Einstein proved that if quantum theory was correct, then pairs of widely spaced objects could be entangled like two flies tangled up in a spider’s web. Weirdly, the entanglement did not diminish, however far apart you allowed the objects to move.

    Einstein called entanglement “spooky action at a distance”. He was sure that his discovery would do away with the theory of quantum mechanics once and for all, but this was not to be.

    Since the 1980s physicists have demonstrated time and again that quantum entanglement is real. However much he hated it, Einstein’s prediction was right and to his chagrin, quantum theory was correct. Things at a distance could be entangled.

    Today physicists have got used to the ‘spookiness’, and the theory of entanglement has been harnessed for the sending of secret codes that cannot be intercepted.

    Around the world, organisations such as Google and IBM and academic laboratories are trying to create quantum computers that depend on entanglement.

    And now Zhao and colleagues want to use the concept of entanglement to create the new gravitational wave detector’s design.

    A new way to measure gravitational waves

    The exciting aspect of the new detector design is that it is actually just a new way of operating existing detectors. It simply uses the detector twice.

    One time, photons in the detector are altered by the gravitational wave so as to pick up the waves. The second time, the detector is used to change the quantum entanglement in such a way that the noise due to quantum uncertainty is not detected.

    The only thing that is detected is the motion of the distant mirrors caused by the gravitational wave. The quantum noise from the uncertainty principle does not appear in the measurement.

    To make it work, you have to start with entangled photons that are created by a device called a quantum squeezer. This technology was pioneered for gravitational wave astronomy at Australian National University, and is now an established technique.

    Like many of the best ideas, the new idea is a very simple one, but one that took enormous insight to recognise. You inject a minuscule amount of squeezed light from a quantum squeezer, and use it twice!

    Around the world physicists are getting ready to test the new theory and find the best way of implementing it in their detectors.

    One of these is the GEO gravitational wave detector at Hannover in Germany, which has been a test bed for many of the new technologies that allowed last year’s momentous discovery of gravitational waves.

    6
    http://www.geo600.org GEO600 aims at the direct detection of Einstein’s gravitational waves by means of a laser interferometer.

    See the full article here .

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  • richardmitnick 9:17 am on May 18, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT Advanced aLigo, , Things that go “chirp” in the night   

    From astrobites: “Things that go “chirp” in the night” 

    Astrobites bloc

    Astrobites

    May 18, 2017
    Kelly Malone

    Title: Electromagnetic Chirps from Neutron Star-Black Hole Mergers
    Authors: Jeremy Schnittman, Tito Dal Canton, Jordan Camp, David Tsang, and Bernard Kelly
    First Author’s Institution: NASA Goddard Space Flight Center and Joint Space-Science Institute

    2
    UMd JSI
    Status: Submitted to the Astrophysical Journal, open access

    One of the biggest scientific accomplishments of the last few years was the discovery of gravitational waves by the LIGO Collaboration, which you can read about on Astrobites here.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    There is, of course, still plenty of work to be done in this field. For example, no experiment has definitively detected an electromagnetic counterpart (which would give off radiation somewhere in the electromagnetic spectrum) to a gravitational wave, although the Fermi Gamma-ray Burst Monitor may have seen hints of one.

    NASA/Fermi LAT

    Detecting such a component would be scientifically interesting for many reasons. The authors of today’s paper give us two such reasons: first, LIGO currently only has a rudimentary ability to localize where in the sky gravitational waves are coming from. Identifying the specific galaxy that produced the gravitational wave would allow us to constrain certain astrophysical models. Second, we could possibly combine an electromagnetic (EM) counterpart with a sub-threshold gravitational wave signal (one that is not statistically significant on its own) to gleam more information about astrophysical events.

    Some models of blacks holes merging with neutron stars call for short gamma-ray bursts (the brightest EM explosions to be observed anywhere in the Universe) to be produced by the merger. This is the same process that produces some gravitational waves. For some of these GRBs, there is a “precursor” gamma-ray flare a few seconds before the peak of the GRB emission. This may seem like only a short amount of time, but since the black hole and neutron star are orbiting each other very rapidly, this event would occur hundreds of orbits before the merger actually occurs. The environment here includes some of the most extreme forces in the known universe, and all the particles involved are extremely relativistic (traveling close to the speed of light). Therefore, the light curve for the precursor flare that eventually reaches the observer on Earth will be affected by phenomena such as relativistic Doppler beaming and gravitational lensing.

    Gravitational Lensing NASA/ESA


    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

    The former makes the light appear at a different luminosity than it actually is and the latter causes the light to bend on its way to us. The authors explain that all the physics combines to give off an electromagnetic “chirp”, similar to the “chirps” that gravitational waves give off. Therefore, it is conceivable that algorithms similar to those used by the LIGO collaboration could be used to search for the electromagnetic chirps.

    The authors used a Monte Carlo radiation transport code to calculate the light curves and the resulting spectra on Earth. Free parameters included the masses of the neutron star and black hole, along with the separation between them. Figure 1 shows what the thermal emission coming from the surface of the neutron star would like like over time, from the point of view of an observer looking at it edge-on (see the caption for details). They note that the inclination angle of the observer does effect their results, with the Einstein ring, a signature of gravitational lensing, only being visible at high angles. However, at smaller angles a modulation from the relativistic beaming is still present.

    3
    Figure 1: An illustration showing what the neutron star/black hole system would look like to an edge-on observer at different times. In a) the ring is caused by gravitational lensing effects. b) is the point of maximum blueshift. c) shows a weaker gravitational lensing effect, and d) is the point of maximum redshift.

    As the system gives off gravitational radiation, the distance between the black hole and the neutron star decreases with the size of the orbit. This causes the frequency and amplitude of the light curve to describe above to increase, and a “chirp”, just like in the gravitational wave signal, is observed. See the figure below for an illustration of the inspiral. The different features of the light curve (from the gravitational lensing and the beaming) dominate at different times here, and from this the black hole mass can be determined. If the light curve is precise enough, the neutron star radius and equation of state could even be determined.

    4
    Figure 2: The electromagnetic modulation for the inspiral of a neutron star/black hole binary merger (initial separation 50 solar masses), with the zoomed in portions corresponding to the beginning and the end.

    The authors do note that the luminosity range where the EM “chirp” could be detected using satellites such as Fermi GBM is fairly small: if it is too bright, a fireball will occur that would mask the chirp. They end the paper by observing that there are still chirps that could be detected with current technologies, and that future gravitational wave observatories such as LISA could potentially work as a trigger for electromagnetic experiments to target their observations.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    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. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 3:50 pm on May 16, 2017 Permalink | Reply
    Tags: , Blind studies, Caltech/MIT Advanced aLigo, , , , , , ,   

    From Symmetry: “The facts and nothing but the facts” 

    Symmetry Mag

    Symmetry

    1
    Artwork by Corinne Mucha

    05/16/17
    Manuel Gnida

    At a recent workshop on blind analysis, researchers discussed how to keep their expectations out of their results.

    Scientific experiments are designed to determine facts about our world. But in complicated analyses, there’s a risk that researchers will unintentionally skew their results to match what they were expecting to find. To reduce or eliminate this potential bias, scientists apply a method known as “blind analysis.”

    Blind studies are probably best known from their use in clinical drug trials, in which patients are kept in the dark about—or blind to—whether they’re receiving an actual drug or a placebo. This approach helps researchers judge whether their results stem from the treatment itself or from the patients’ belief that they are receiving it.

    Particle physicists and astrophysicists do blind studies, too. The approach is particularly valuable when scientists search for extremely small effects hidden among background noise that point to the existence of something new, not accounted for in the current model. Examples include the much-publicized discoveries of the Higgs boson by experiments at CERN’s Large Hadron Collider and of gravitational waves by the Advanced LIGO detector.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    “Scientific analyses are iterative processes, in which we make a series of small adjustments to theoretical models until the models accurately describe the experimental data,” says Elisabeth Krause, a postdoc at the Kavli Institute for Particle Astrophysics and Cosmology, which is jointly operated by Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory. “At each step of an analysis, there is the danger that prior knowledge guides the way we make adjustments. Blind analyses help us make independent and better decisions.”

    Krause was the main organizer of a recent workshop at KIPAC that looked into how blind analyses could be incorporated into next-generation astronomical surveys that aim to determine more precisely than ever what the universe is made of and how its components have driven cosmic evolution.

    Black boxes and salt

    One outcome of the workshop was a finding that there is no one-size-fits-all approach, says KIPAC postdoc Kyle Story, one of the event organizers. “Blind analyses need to be designed individually for each experiment.”

    The way the blinding is done needs to leave researchers with enough information to allow a meaningful analysis, and it depends on the type of data coming out of a specific experiment.

    A common approach is to base the analysis on only some of the data, excluding the part in which an anomaly is thought to be hiding. The excluded data is said to be in a “black box” or “hidden signal box.”

    Take the search for the Higgs boson. Using data collected with the Large Hadron Collider until the end of 2011, researchers saw hints of a bump as a potential sign of a new particle with a mass of about 125 gigaelectronvolts. So when they looked at new data, they deliberately quarantined the mass range around this bump and focused on the remaining data instead.

    They used that data to make sure they were working with a sufficiently accurate model. Then they “opened the box” and applied that same model to the untouched region. The bump turned out to be the long-sought Higgs particle.

    That worked well for the Higgs researchers. However, as scientists involved with the Large Underground Xenon experiment reported at the workshop, the “black box” method of blind analysis can cause problems if the data you’re expressly not looking at contains rare events crucial to figuring out your model in the first place.

    LUX has recently completed one of the world’s most sensitive searches for WIMPs—hypothetical particles of dark matter, an invisible form of matter that is five times more prevalent than regular matter.

    LUX/Dark matter experiment at SURF

    LUX scientists have done a lot of work to guard LUX against background particles—building the detector in a cleanroom, filling it with thoroughly purified liquid, surrounding it with shielding and installing it under a mile of rock. But a few stray particles make it through nonetheless, and the scientists need to look at all of their data to find and eliminate them.

    For that reason, LUX researchers chose a different blinding approach for their analyses. Instead of using a “black box,” they use a process called “salting.”

    LUX scientists not involved in the most recent LUX analysis added fake events to the data—simulated signals that just look like real ones. Just like the patients in a blind drug trial, the LUX scientists didn’t know whether they were analyzing real or placebo data. Once they completed their analysis, the scientists that did the “salting” revealed which events were false.

    A similar technique was used by LIGO scientists, who eventually made the first detection of extremely tiny ripples in space-time called gravitational waves.

    High-stakes astronomical surveys

    The Blind Analysis workshop at KIPAC focused on future sky surveys that will make unprecedented measurements of dark energy and the Cosmic Microwave Background—observations that will help cosmologists better understand the evolution of our universe.

    CMB per ESA/Planck

    ESA/Planck

    Dark energy is thought to be a force that is causing the universe to expand faster and faster as time goes by. The CMB is a faint microwave glow spread out over the entire sky. It is the oldest light in the universe, left over from the time the cosmos was only 380,000 years old.

    To shed light on the mysterious properties of dark energy, the Dark Energy Science Collaboration is preparing to use data from the Large Synoptic Survey Telescope, which is under construction in Chile. With its unique 3.2-gigapixel camera, LSST will image billions of galaxies, the distribution of which is thought to be strongly influenced by dark energy.


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam


    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.

    “Blinding will help us look at the properties of galaxies picked for this analysis independent of the well-known cosmological implications of preceding studies,” DESC member Krause says. One way the collaboration plans on blinding its members to this prior knowledge is to distort the images of galaxies before they enter the analysis pipeline.

    Not everyone in the scientific community is convinced that blinding is necessary. Blind analyses are more complicated to design than non-blind analyses and take more time to complete. Some scientists participating in blind analyses inevitably spend time looking at fake data, which can feel like a waste.

    Yet others strongly advocate for going blind. KIPAC researcher Aaron Roodman, a particle-physicist-turned-astrophysicist, has been using blinding methods for the past 20 years.

    “Blind analyses have already become pretty standard in the particle physics world,” he says. “They’ll be also crucial for taking bias out of next-generation cosmological surveys, particularly when the stakes are high. We’ll only build one LSST, for example, to provide us with unprecedented views of the sky.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 9:40 am on May 16, 2017 Permalink | Reply
    Tags: , , , , Caltech/MIT Advanced aLigo, , , Hunting for ECOs: Gravitational Wave 'Smoking Guns'   

    From astrobites: “Hunting for ECOs: Gravitational Wave ‘Smoking Guns'” 

    Astrobites bloc

    Astrobites

    May 16, 2017
    Lisa Drummond

    Title: Gravitational-wave signatures of exotic compact objects and of quantum corrections at the horizon scale
    Authors: Vitor Cardoso, Seth Hopper, Caio F. B. Macedo, Carlos Palenzuela, Paolo Pani
    First Author’s Institution: Universidade de Lisboa
    1
    Status: Physical Review D, open access

    An exotic compact object (ECO) consists of matter that is not electrons, neutrons, protons or muons. There have been numerous “exotic” astronomical objects proposed (for example, quark stars, boson stars and preon stars) but none of these hypothetical stars have been detected. Up until recently, detecting objects that do not radiate electromagnetically has been challenging for astronomers and only accomplished indirectly. With the advent of the emerging field of gravitational wave astronomy, we have the ability to directly detect ECOs (if they exist) – we just need to know the gravitational wave “smoking gun” to look for!


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    But why study ECOs at all, given we don’t know if they exist? Even as purely hypothetical objects, they are useful as tractable toy models for testing consequences of general relativity. In addition, they could play a role in solving some of the biggest mysteries in the Universe – boson stars, for example, have been considered as potential dark matter candidates (see here). And if they do exist, we need to be able to know how to distinguish their gravitational wave signals from those of objects that have already been observed.

    This brings us to today’s astrobite. Firstly, the authors simulate bouncing a wave packet off the gravitational potential of several different models of ECOs and observe that, qualitatively, ultra-compact objects have a universal signature in their response. Secondly, the authors investigate the complementary problem of boson stars colliding. Boson stars are chosen because they are ECOs whose formation can potentially occur in dynamical scenarios and they are relatively simple to treat numerically.

    Echoes of ECOs

    2
    Figure 1: The spacetime around very massive objects like stars and black holes is distorted due to their gravitational field. If the same amount of mass is packed into a smaller region of space, there will be a more significant effect on the gravitational field and consequently a more distorted region of space time surrounding them. Image source: https://medium.com/starts-with-a-bang/astroquizzical-how-does-gravity-escape-from-a-black-hole-5ef156bf048d

    Figure 1 compares the distortion of spacetime due to the gravitational fields of the Sun, a neutron star and a black hole; what we see is that if the same mass is packed into a more compact region, the surrounding gravitational forces are more extreme. In some sense, ECOs are halfway between conventional compact objects that are made of matter (such as neutron stars) and black holes (where all the mass has been compacted into a singular point through gravitational collapse). ECOs are not point-like, but have the potential to be compact enough to exhibit some black-hole-like properties. For example, ECOs can have photon spheres, which only exist around ultra-compact objects.

    A photon sphere is a region of space around an object (typically a black hole, but potentially also ECOs) where photons travel in orbits (see Figure 2).

    3
    igure 2: Arrows depict possible orbits of photons around a black hole. The dotted circle is the photon sphere. Image source: http://www.realclearscience.com/blog/2015/07/can_light_orbit_massive_objects.html

    It is typically unstable for a black hole and small perturbations will push the photon out of orbit. However, ECOs do not have event horizons, which are boundaries around a black hole beyond which light cannot escape.

    When you hit a bell, it vibrates; the surface of the bell oscillates between different configurations until the vibration is damped and the ringing stops. Similarly if you “hit” a black hole by bouncing another mass off of it, it “rings” until it is stationary again (see Figure 3). A black hole is a cosmic bell that will “ring” by oscillating in shape between a elongated sphere and a flattened sphere. The damping of the ringing by the emission of gravitational waves is called ringdown. Orbits of a photon around a black hole spacetime can be understood in terms of an “effective potential” whose peaks (troughs) are locations of unstable (stable) photon spheres. There is a close correspondence between this potential and the potential felt by the vibrations of the black hole (discussed in detail here).

    4
    Figure 3: After a perturbation, the black hole “rings” by changing shape, oscillating between an elongated and flattened spheroid. It produces gravitational waves during this “ringdown” phase until it is stationary once more. Image source: http://slideplayer.com/slide/4179737/

    To study the ringdown signal, the authors simulate bouncing a wave packet off both a black hole and an ECO. The initial ringdown of the ECO is identical to the black hole [Physical Review Letters]. This initial signal corresponds to the “ringing” of the photon sphere and is rapidly damped. Crucially, ECOs have a stellar surface rather than an event horizon, meaning they can also have an inner photon sphere that is stable. The main burst of radiation can then reflect off the potential barrier at the inner photon sphere (the potential barrier shape is given in Figure 4) rather than getting absorbed at the event horizon.

    5
    Figure 4: Qualitative features of the potential felt by perturbations of a black hole (top) and ECOs (bottom). The wormhole (middle) is another exotic object which we do not discuss in this bite. The maximum and minimum of the potential correspond to the locations of the unstable outer photon sphere and the stable inner photon sphere respectively. Figure 1 in paper.

    Consquently, after the initial ringdown signal, there are “echoes” from the inner photon sphere. In summary, the signal gets “trapped” in the cavity between the outer and inner photon spheres and leaks out after a time delay \Delta t . Therefore, the characteristic signature of an ultra-compact object without an event horizon is a series of distorted echoes following well after the initial ringdown signal has died away. This is exactly the effect we see in Figure 5.

    6
    Figure 5: Gravitational waveform for the infall of a test particle into a black hole (dotted black line) and an ECO (red line). The initial ringdown caused by the ringing of the outer photon sphere are present for both the black hole and ECO signal. The pulse then travels inward and is either absorbed by the event horizon (in the black hole case) or bounces off the inner photon sphere in the ECO case, leading to subsequent echoes in the signal. Figure 3 in paper.

    Colliding Boson Stars

    Now, we are ready to tackle the next topic of the paper: colliding boson stars. This scenario is complementary to the echo signatures found in the ringdown of ECOs; here the purpose is to investigate gravitational waves produced by fairly viable ECOs (boson stars) rather than more contrived objects such as wormholes or gravastars.

    8
    A model of ‘folded’ space-time illustrates how a wormhole bridge might form with at least two mouths that are connected to a single throat or tube.
    Credit: edobric | Shutterstock

    7
    https://futurism.com/the-gravastar-an-alternative-to-black-holes/

    The authors answer the question of whether boson stars can mimic black holes in different scenarios.

    Boson stars are in general much less compact than black holes and therefore only very finely-tuned boson stars will actually have a photon sphere, so the echo effects discussed in the previous section are only marginally relevant here. Nonetheless, boson star collisions exhibit distinctive and sometimes quite exotic behaviour that is qualitatively different to black hole collisions with the same masses. In certain cases, the two stars actually annihilate during the merger, while in other scenarios there is a repulsive force between the stars so they bounce back and forth until they lose all their kinetic energy and settle back into a binary.

    The phenomena discussed in this paper are quite exotic. However, it is important to remember that gravitational wave astronomy gives us, more than ever before, the opportunity for exciting and unexpected discoveries which challenge known physics – and we need to be proactive in looking for them!

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    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. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 6:57 am on May 16, 2017 Permalink | Reply
    Tags: Caltech/MIT Advanced aLigo, , EPR paradox, , , , , Spooky action at a distance   

    From COSMOS: “Using Einstein’s ‘spooky action at a distance’ to hear ripples in spacetime” 

    Cosmos Magazine bloc

    COSMOS

    16 May 2017
    Cathal O’Connell

    1
    The new technique will aid in the detection of gravitational waves caused by colliding black holes. Henze / NASA

    In new work that connects two of Albert Einstein’s ideas in a way he could scarcely have imagined, physicists have proposed a way to improve gravitational wave detectors, using the weirdness of quantum physics.

    The new proposal, published in Nature Physics, could double the sensitivity of future detectors listening out for ripples in spacetime caused by catastrophic collisions across the universe.

    When the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves in late 2015 it was the first direct evidence of the gravitational waves Einstein had predicted a century before.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    Now it another of Einstein’s predictions – one he regarded as a failure – could potentially double the sensitivity of LIGOs successors.

    The story starts with his distaste for quantum theory – or at least for the fundamental fuzziness of all things it seemed to demand.

    Einstein thought the universe would ultimately prove predictable and exact, a clockwork universe rather than one where God “plays dice”. In 1935 he teamed up with Boris Podolsky and Nathan Rosen to publish a paper they thought would be a sort of reductio ad absurdum. They hoped to disprove quantum mechanics by following it to its logical, ridiculous conclusion. Their ‘EPR paradox’ (named for their initials) described the instantaneous influence of one particle on another, what Einstein called “spooky action at a distance” because it seemed at first to be impossible.

    Yet this sally on the root of quantum physics failed, as the EPR effect turned out not to be a paradox after all. Quantum entanglement, as it’s now known, has been repeatedly proven to exist, and features in several proposed quantum technologies, including quantum computation and quantum cryptography.

    2
    Artistic rendering of the generation of an entangled pair of photons by spontaneous parametric down-conversion as a laser beam passes through a nonlinear crystal. Inspired by an image in Dance of the Photons by Anton Zeilinger. However, this depiction is from a different angle, to better show the “figure 8” pattern typical of this process, clearly shows that the pump beam continues across the entire image, and better represents that the photons are entangled.
    Date 31 March 2011
    Source Entirely self-generated using computer graphics applications.
    Author J-Wiki at English Wikipedia

    Now we can add gravity wave detection to the list.

    LIGO works by measuring the minute wobbling of mirrors as a gravitational wave stretches and squashes spacetime around them. It is insanely sensitive – able to detect wobbling down to 10,000th the width of a single proton.

    At this level of sensitivity the quantum nature of light becomes a problem. This means the instrument is limited by the inherent fuzziness of the photons bouncing between its mirrors — this quantum noise washes out weak signals.

    To get around this, physicists plan to use so-called squeezed light to dial down the level of quantum noise near the detector (while increasing it elsewhere).

    The new scheme aids this by adding two new, entangled laser beams to the mix. Because of the ‘spooky’ connection between the two entangled beams, their quantum noise is correlated – detecting one allows the prediction of the other.

    This way, the two beams can be used to probe the main LIGO beam, helping nudge it into a squeezed light state. This reduces the noise to a level that standard quantum theory would deem impossible.

    The authors of the new proposal write that it is “appropriate for all future gravitational-wave detectors for achieving sensitivities beyond the standard quantum limit”.

    Indeed, the proposal could as much as double the sensitivity of future detectors.

    Over the next 30 years, astronomers aim to improve the sensitivity of the detectors, like LIGO, by 30-fold. At that level, we’d be able to hear all black hole mergers in the observable universe.

    ESA/eLISA, the future of gravitational wave research

    However, along with improved sensitivity, the proposed system would also increase the number of photons lost in the detector. Raffaele Flaminio, a physicist at the National Astronomical Observatory of Japan, points out in a perspective piece for Nature Physics [no link], Flaminio that the team need to do more work to understand how this will affect ultimate performance.

    “But the idea of using Einstein’s most famous (mistaken) paradox to improve the sensitivity of gravitational-wave detectors, enabling new tests of his general theory of relativity, is certainly intriguing,” Flaminio writes. “Einstein’s ideas – whether wrong or right – continue to have a strong influence on physics and astronomy.”

    See the full article here .

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  • richardmitnick 1:45 pm on March 29, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT Advanced aLigo, , ,   

    From aeon: “Echoes of a black hole” 

    1

    aeon

    1
    An infrared image from NASA’s Spitzer Space Telescope shows the centre of the Milky Way galaxy where the brightest white spot marks the site of a supermassive black hole
    http://www.spitzer.caltech.edu/images/1541-ssc2006-02a1-Spitzer-View-of-the-Center-of-the-Milky-Way

    3.29.17
    Sabine Hossenfelder

    A billion years ago, two dancing black holes make a final spin, merge, and – in a matter of seconds – release a cataclysmic amount of energy. Much as a falling pebble spreads waves on the surface of a still lake, the merger initiates gravitational waves in the space-time continuum. Fast-forward to planet Earth and the year 2015. After an immense journey, the gravitational waves from the black-hole merger pass through our solar system. On the morning of 14 September, they oh-so-slightly wiggle the arms of the twin Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in Louisiana and Washington state.



    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Niayesh Afshordi at the University of Waterloo in Canada first heard of LIGO’s seminal detection over lunch in a bistro. It was late 2015 and still weeks to go until the results were officially released. But rumours were buzzing, and a colleague who had seen the unpublished paper spilled the beans. Afshordi, an astrophysicist who also works at the Perimeter Institute in Waterloo, instantly appreciated the importance of the news – both for the physics community at large, and for his own unconventional theory about the construction of the Universe.

    ‘I had an existential crisis at some point. I thought all the problems in cosmology had been solved,’ Afshordi recalled. ‘But then I came up with this idea that dark energy is made by black holes.’ Studies of distant stellar explosions and other lines of evidence show that our universe grows at an accelerating pace, but nobody knows the cause. Matter alone cannot have this effect, so cosmologists blame the expansion on a peculiar type of energy, called dark energy. Its origin and nature were, and are, a mystery.

    In 2009, Afshordi, together with his colleagues Chanda Prescod-Weinstein and Michael Balogh, put forward a theory according to which black holes seed a long-range field that mimics dark energy. The field spills out from black holes and spans through the Universe. It’s an intriguing explanation for the origin of dark energy and, by Afshordi’s calculations, the number of black holes estimated to exist should create just about the right amount of field energy to fit the observations.

    But Afshordi’s idea overthrows what physicists believed they knew about black holes. In Albert Einstein’s theory of general relativity, the event horizon of a black hole – the surface beyond which there is no escape – is insubstantial. Nothing special happens upon crossing it, just that there is no turning around later. If Afshordi is right, however, the inside of the black hole past the event horizon no longer exists. Instead, a Planck-length away from where the horizon would have been, quantum gravitational effects become large, and space-time fluctuations go wild. (The Planck length is a minuscule distance: about 10-35 metres, or 10-20 times the diameter of a proton.) It’s a complete break with relativity.

    When he heard of the LIGO results, Afshordi realised that his so-far entirely theoretical idea could be observationally tested. If event horizons are different than expected, the gravitational-wave bursts from merging black holes should be different, too. Events picked up by LIGO should have echoes, a subtle but clear signal that would indicate a departure from standard physics. Such a discovery would be a breakthrough in the long search for a quantum theory of gravity. ‘If they confirm it, I should probably book a ticket to Stockholm,’ Afshordi said, laughing.

    Quantum gravity is the missing unification of general relativity with the quantum field theories of the standard model of particle physics. If just thrown together, the two theories lead to internal contradictions, and fail to make sense. Black holes are one of the most studied examples for such a contradiction. Use quantum field theory near the horizon and you find that the black hole emits particles, slowly evaporating. Those particles carry away mass but, as Stephen Hawking demonstrated in the 1970s, they cannot carry information about what formed the black hole. And so, if the black hole evaporates entirely, all the information about what fell in has been destroyed. In quantum field theory, however, information is always preserved. Something in the mathematics, therefore, doesn’t fit correctly.

    The culprit, most physicists think, is that the calculation doesn’t take into account the quantum behaviour of space and time because the theory for this – quantum gravity – is still unknown. For decades, physicists thought that the quantum gravitational effects necessary to solve the black-hole conundrum were hidden behind the event horizon. They thought that it is only near the singularity, at the centre of the black hole, that the effects of quantum gravity become relevant. But recently, they have had to rethink.

    In 2012, a group of researchers from the University of California, Santa Barbara, found an unexpected consequence of the currently favoured idea that information somehow escapes with the radiation from a black hole. To make the idea work, large deviations from general relativity are required, not only near the singularity but also at the event horizon. Those deviations would create what the researchers dubbed a ‘black hole firewall’, a barrier of high energy just outside the horizon.

    Such a firewall (if it exists) would become noticeable only for an infalling observer, and would not emit observable signatures that could show up in our telescopes. However, the firewalls lent support to Afshordi’s earlier idea that black holes create a field that acts as dark energy. If that was so, then the near-horizon region of black holes should be very different from what general relativity predicts; a firewall that solves the black hole information-loss problem could be one effect of that deviation. Afshordi’s proposal for how to modify general relativity might therefore hold the key to resolving the tension between quantum theory and general relativity. It was an idea that wouldn’t let him go.

    When he learned of LIGO’s first detection, Afshordi began to explore whether the gravitational waves emitted from a black-hole merger could reveal intimate details about what happens near the black-hole horizon. At first it seemed too much to hope for. ‘I didn’t really think we could see quantum gravity effects in the gravitational-wave signal because we had already looked in so many places,’ Afshordi said. ‘But I changed my mind about this.’

    What made Afshordi reconsider was work by Vítor Cardoso and colleagues at the Instituto Superior Técnico in Portugal on gravitational-wave echoes from black holes. Cardoso had laid out on general grounds that a merger of two objects that are compact but do not have an event horizon would produce gravitational waves very similar to those of black holes – similar, but not identical. The key feature indicating the horizon’s absence, Cardoso argued, would be a periodic recurrence in the signal from the merger. Instead of a single peak followed by a ringdown (think a big splash on a pond, and then rapidly dissipating ripples), the gravitational waves should come as a series of fading pulses – fainter echoes of the original event. Afshordi found that the near-horizon modification described by his theory would cause exactly such echoes. Moreover, he could calculate their recurrence time as a function of the final black hole’s mass, allowing a precise prediction.

    Nobody had ever sought such a signal before, and finding it would not be easy. So far there are only two public, well-defined gravitational-wave detections from LIGO. Together with a collaborator, Afshordi analysed the LIGO data for traces of echoes. By comparing the openly available recordings to random noise, they found an echo at the calculated recurrence time. The statistical significance is not high, however. In scientific terms, it has an estimated significance of 2.9 sigma. Such a signal can be caused by pure noise with a chance of about a one-in-200. In physics, an event of such low confidence is interesting but does not amount to a discovery.

    The LIGO experiment is really just getting started, however. The most remarkable thing about the first two gravitational wave events is that the facilities were able to record them at all. The technological challenges were tremendous. Each site, both in Louisiana and in Washington state, has an interferometer with two perpendicular arms about 4 kilometres long in which a laser beam bounces back and forth between mirrors; when recombined, the beams interfere with each other. Interference of the laser’s light-waves is sensitive to deformations in the arms’ relative length as little as a thousandth the diameter of a proton. That is the level of sensitivity required to pick up gravitational effects of colliding black holes.

    A gravitational wave passing through the interferometer deforms both arms at different times, thereby skewing the interference pattern. Requiring an event to be recorded at both sites provides protection against false alarms. By design, LIGO detects gravitational waves best at wavelengths of hundreds to thousands of kilometres, the range expected for black-hole mergers. Other gravitational-wave detectors are planned to cover different parts of the spectrum, each tuned to different types of phenomena.

    Gravitational waves are an unavoidable prediction of general relativity. Einstein recognised that space-time is dynamic – it stretches, it curves, and it wiggles in response to gravitational disturbances. When it wiggles, the waves can travel freely into the far distance, carrying away energy and manifesting themselves by a periodic expansion and contraction of space in orthogonal directions. We have long had indirect evidence for gravitational waves. Because they carry away energy, they cause a small but measurable decay in the mutual orbit of binary pulsars. This effect was first observed in the 1970s, and was awarded a Nobel Prize in 1993. But until LIGO’s detection, we had no direct evidence for the existence of gravitational waves.

    LIGO’s first event – the September 2015 detection that so excited Afshordi – was remarkable, and not only because it happened just a few days after a long-planned instrumental upgrade. It stood out also because the merging black holes were so heavy, with masses estimated at 29 and 36 times the Sun’s mass. ‘A lot of people expected the black hole events to have lower masses,’ said Ofek Birnholtz, a member of the LIGO collaboration’s group on compact binary coalescence and a physicist at the Max Planck Institute in Germany. The strikingly clean signal, together with the collaboration’s openness in sharing the data, has been an inspiration for physicists in other communities who, like Afshordi, are now exploring how to use the new observations for their own work.

    On 26 December 2015, LIGO recorded a second event. The age of gravitational-wave astronomy had officially begun, after many years of slow progress and false starts. ‘Some of my PhD colleagues had left the field of gravitational-wave astronomy,’ Birnholtz said and added, laughing, ‘but are returning because suddenly it’s hot again.’ This is uncharted territory, basic research at its finest. What kind of black hole and compact stellar systems are there? Where are they within the galaxies? What do the gravitational waves reveal about their origins? If a neutron star merges with a black hole, what can be learned about matter in such extreme conditions? Do black holes behave the way that our calculations predict?

    Afshordi’s theory of black holes and dark energy is just one example of the kinds of enquiries that are now possible. A wealth of information is waiting to be explored, openly, around the world.

    A few days after Afshordi’s result appears on the open-access server arXiv.org, members of the LIGO collaboration scrutinise the analysis. It takes only a few weeks until they publish a reply, criticise the methodology, and call for different statistical tools. Birnholtz is one of the authors of that criticism.

    ‘The claim is surprising,’ said Birnholtz. ‘I have no prior as to whether or not there should be echoes. That’s physics nobody can guess at. But I do have a strong intuition, working with LIGO data, that the amplitude is probably not large enough to claim such a significance at this stage.’ Birnholtz has suggestions for how to improve the analysis, but avoids making statements about the chances of confirming the result. Alex Nielsen, another member of the LIGO collaboration and one of Birnholtz’s co-authors, reiterates the need for caution: ‘As members of the LIGO collaboration, we have to be very careful about what statements we make in public, before we have full collaboration approval. But the data is public and people can do with it what they want.’

    The LIGO collaboration has an open science centre, where data recorded for one hour around the time of confirmed gravitational events is publicly available. ‘People are welcome to use it and contact us for any questions,’ Birnholtz said. ‘If they find anything interesting, they can share it with us, and we can work on it together. This is part of the scientific experience.’

    The collaboration has several thousand members worldwide, distributed at more than a hundred institutions. They meet twice a year; the most recent meeting was in March in Pasadena, California. Some members of the collaboration are now trying to reproduce Afshordi’s analysis. Birnholtz expects the effort to take several months. ‘The result might be disappointing,’ he warned. ‘Not in that it says there are no echoes, but that we can’t say whether there are echoes.’ Gravitational-wave astronomy is still a field in its infancy, though, and much more data are on the way. The collaboration estimates that by the completion of the third observing run in 2018, LIGO is likely to have made 40 high-quality detections of black-hole mergers. Each will offer another opportunity to test Afshordi’s theory.

    Because they interact so weakly and deposit so little energy as they pass by, gravitational waves are exceedingly difficult to measure. The deformation they cause is tiny, and enormous care is necessary to extract a clean signal. The discovery threshold used by the LIGO collaboration is 5 sigma, corresponding to a chance of less than one in 3 million that the signal was coincidence, which is far above the significance level of Afshordi’s signal. The weak interaction of gravitational waves, however, is also the reason why they are excellent messengers. Unlike particles or light, they are barely affected on their way to us, carrying with them pristine information about where and how they were generated. They allow entirely new precision tests of general relativity in a regime that has never before been explored.

    If black hole echoes should be confirmed, that would almost certainly indicate a stark deviation from general relativity. Finding echoes would not uniquely confirm Afshordi’s theory that black holes seed dark energy. But some truly novel idea would be needed to explain it. ‘I don’t know of such echoes in any simulation that we have done to date,’ Birnholtz said. ‘If we were to confirm that there was an echo, that would be very interesting. We would have to look into what could produce such an echo.’

    Afshordi has research plans in case the statistical significance of his signal increases. He wants to improve his model of black-hole mergers, and run a numerical simulation to support the analytical estimate of what the echoes should look like. The next step would then be to better understand the underlying theory of space-time that could give rise to such a behaviour of the black-hole horizon. Cosmologists would also want to look much more closely at the implications of this new explanation for dark energy.

    Afshordi is aware just how speculative it is to alter general relativity so drastically. But he’s a rebel with a mission: ‘I want to encourage people to keep an open mind and not to dismiss ideas because they don’t match their preconceived notions.’ With LIGO exposing the workings of the Universe in ways never before studied, a lot of preconceived notions may soon be set aside.

    See the full article here .

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  • richardmitnick 6:12 pm on March 7, 2017 Permalink | Reply
    Tags: , Caltech/MIT Advanced aLigo, , , ,   

    From APS: “Gravitational Waves: Hints, Allegations, and Things Left Unsaid” 

    AmericanPhysicalSociety

    American Physical Society

    APS April Meeting 2017

    If the APS April Meeting 2016 was a champagne-soaked celebration for gravitational wave scientists, the 2017 meeting was more like spring training — there was lots of potential, but the real action is yet to come.



    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    The Laser Interferometer Gravitational-Wave Observatory, or LIGO, launched the era of gravitational wave astronomy in February 2016 with the announcement of a collision between two black holes observed in September 2015. “I’m contractually obligated to show the slide [of the original detection] at any LIGO talk for at least another year,” joked Jocelyn Read, a physicist at California State University, Fullerton, during her presentation at this year’s meeting.

    The scientific collaboration that operates the two LIGO detectors netted a second merger between slightly smaller black holes on December 26, 2015. (A third “trigger” showed up in LIGO data on October 12, 2015, but ultimately did not meet the stringent “five-sigma” statistical significance standard that physicists generally insist on.)

    The detectors then went offline in January 2016 for repairs and upgrades. The second observing run began on November 30, but due to weather-related shutdowns and other logistical hurdles, the two detectors had operated simultaneously on only 12 days as of this year’s meeting, which limited the experiment’s statistical power. Collaboration members said they had no new detections to announce.

    Instead, scientists focused on sharpening theoretical estimates of how often various events occur. In particular, they are eager to see collisions involving neutron stars, which lack sufficient mass to collapse all the way to a black hole. Neutron star collisions are thought to be plentiful, but would emit weaker gravitational waves than do mergers of more massive black holes, so the volume of space the LIGO detectors can scan for such events is smaller.

    Even with recent upgrades, failure to detect a neutron star merger during the current observing run would not rule out existing models, said Read. But she added that with future improvements and the long-anticipated addition of Virgo, a LIGO-like detector based in Cascina, Italy, neutron stars should soon come out of hiding.



    VIRGO Gravitational Wave interferometer, near Pisa, Italy [Not yet operational]

    “We’re expecting that with a little more volume and a little more time, we’re going to be starting to make some astrophysically interesting statements.”

    LIGO scientists are also looking for signals from individual pulsars — rapidly rotating neutron stars that are observed on earth as pulses of radio waves. A bump on a pulsar’s surface should produce gravitational waves, but so far, no waves with the right shape have been picked up. This absence puts a limit on the size of any irregularities and on the emission power of gravitational waves from nearby pulsars such as the Crab and Vela pulsars, said Michael Landry, head of the Hanford LIGO observatory, and could soon start putting limits on more distant ones.

    Presenters dropped a few hints of possible excitement to come. LIGO data taken through the end of January produced two short signals that were unusual enough to exceed the experiment’s “false alarm” threshold — signals with shapes and strengths expected to show up once a month or less by chance alone. Both LIGO collaboration members and astronomers at conventional telescopes are investigating the data to determine whether they represent real events.

    For now, potential events will continue to be scrutinized by collaboration members, and released to the public via announcements coming months after initial detection. But LIGO leaders expect to shorten the lag time as detections become more frequent, perhaps eventually putting out monthly updates. “We hope to make it quicker,” said LIGO collaboration spokesperson Gabriela González, a physicist at Louisiana State University in Baton Rouge.

    LIGO is not the only means by which scientists are searching for gravitational waves. Some scientists are using powerful radio telescopes to track signals emanating from dozens of extremely fast-rotating pulsars. A specific pattern of correlations between tiny hiccups in the arrival times of these pulses would be a signature of long-wavelength gravitational waves expected from mergers of distant supermassive black holes.

    Teams in the U.S., Europe, and Australia have monitored pulsars for more than a decade, so far without positive results. But in an invited talk, Laura Sampson of Northwestern University in Evanston, Illinois, coyly announced “hints of some interesting signals.” With 11 years of timing data from 18 pulsars tracked by the Green Bank Telescope in West Virginia and the Arecibo Telescope in Puerto Rico, Sampson and other scientists affiliated with a collaboration called NANOGrav have eked out a result with a statistical significance of around 1.5 to 2 sigma.



    GBO radio telescope, Green Bank, West Virginia, USA


    NAIC/Arecibo Observatory, Puerto Rico, USA

    Data from the Green Bank Telescope in West Virginia and Arecibo Telescope in Puerto Rico help researchers use pulsars to study gravitational waves.

    “It’s the first hint we’ve ever had that there might be a signal in the data,” Sampson said. “Everything we’ve done before was straight-up limits.”

    As NANOGrav continues to gather data, their signal could grow toward the 5-sigma gold standard, or it could vanish. Sampson and her colleagues hope to have an answer in the next year or two. “This is of course very exciting news,” said Gonzalez.

    See the full article here .

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    American Physical Society
    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries.

     
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