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  • richardmitnick 3:34 pm on December 11, 2018 Permalink | Reply
    Tags: , , , , , Five Surprising Truths About Black Holes From LIGO, MIT Caltech Advanced aLIGO,   

    From Ethan Siegel: “Five Surprising Truths About Black Holes From LIGO” 

    From Ethan Siegel
    Dec 11, 2018

    1
    A still image of a visualization of the merging black holes that LIGO and Virgo have observed so far. As the horizons of the black holes spiral together and merge, the emitted gravitational waves become louder (larger amplitude) and higher pitched (higher in frequency). The black holes that merge range from 7.6 solar masses up to 50.6 solar masses, with about 5% of the total mass lost during each merger. (TERESITA RAMIREZ/GEOFFREY LOVELACE/SXS COLLABORATION/LIGO-VIRGO COLLABORATION)

    With a total of 10 black holes detected, what we’ve learned about the Universe is truly amazing.

    On September 14th, 2015, just days after LIGO first turned on at its new-and-improved sensitivity, a gravitational wave passed through Earth. Like the billions of similar waves that had passed through Earth over the course of its history, this one was generated by an inspiral, merger, and collision of two massive, ultra-distant objects from far beyond our own galaxy. From over a billion light years away, two massive black holes had coalesced, and the signal — moving at the speed of light — finally reached Earth.

    But this time, we were ready. The twin LIGO detectors saw their arms expand-and-contract by a subatomic amount, but that was enough for the laser light to shift and produce a telltale change in an interference pattern. For the first time, we had detected a gravitational wave. Three years later, we’ve detected 11 of them, with 10 coming from black holes. Here’s what we’ve learned.

    2
    The 30-ish solar mass binary black holes first observed by LIGO are very difficult to form without direct collapse. Now that it’s been observed twice, these black hole pairs are thought to be quite common. But the question of whether black hole mergers emit electromagnetic emission is not yet settled. (LIGO, NSF, A. SIMONNET (SSU))

    There have been two “runs” of LIGO data: a first one from September 12, 2015 to January 19, 2016 and then a second one, at somewhat improved sensitivity, from November 30, 2016 to August 25, 2017. That latter run was, partway through, joined by the VIRGO detector in Italy, which added not only a third detector, but significantly improved our ability to pinpoint the location of where these gravitational waves occurred. LIGO is currently shut down right now, as it’s undergoing upgrades that will make it even more sensitive, as it prepares to begin a new data-taking observing run in the spring of 2019.

    On November 30th, the LIGO scientific collaboration released the results of their improved analysis, which is sensitive to the final stages of mergers between objects between about 1 and 100 solar masses.

    3
    The 11 gravitational wave events detected by LIGO and Virgo, with their names, mass parameters, and other essential information encoded in Table form. Note how many events came in the last month of the second run: when LIGO and Virgo were operating simultaneously. (THE LIGO SCIENTIFIC COLLABORATION, THE VIRGO COLLABORATION; ARXIV:1811.12907)

    The 11 detections that have been made so far are shown above, with 10 of them representing black hole-black hole mergers, and only GW170817 representing a neutron star-neutron star merger. Those merging neutron stars was the closest event at a mere 130–140 million light years away. The most massive merger seen — GW170729 — comes to us from a location that, with the expansion of the Universe, is now 9 billion light years away.

    These two detections are also the lightest and heaviest gravitational wave mergers ever detected, with GW170817 colliding a 1.46 and a 1.27 solar mass neutron star, and GW170729 colliding a 50.6 and a 34.3 solar mass black hole together.

    Here are the five surprising truths that we’ve learned from all of these detections combined.

    4
    LIGO, as designed, should be sensitive to black holes of a particular mass range that inspiral and merge: from 1 up to a few hundred solar masses. The fact that what we observe appears to be capped at 50 solar masses places severe constraints on black hole merger rates above that figure. (NASA / DANA BERRY (SKYWORKS DIGITAL))

    1.) The largest merging black holes are the easiest to see, and they don’t appear to get larger than about 50 solar masses. One of the best things about looking for gravitational waves is that it’s easier to see them from farther away than it is for a light source. Stars appear dimmer in proportion to their distance squared: a star 10 times the distance is just one-hundredth as bright. But gravitational waves are dimmer in direct proportion to distance: merging black holes 10 times as far away produce 10% the signal.

    As a result, we can see very massive objects to very great distances, and yet we don’t see black holes merging with 75, 100, 150, or 200+ solar masses. 20-to-50 solar masses are common, but we haven’t seen anything above that yet. Perhaps the black holes arising from ultra-massive stars truly are rare.

    6
    Aerial view of the Virgo gravitational-wave detector, situated at Cascina, near Pisa (Italy). Virgo is a giant Michelson laser interferometer with arms that are 3 km long, and complements the twin 4 km LIGO detectors. (NICOLA BALDOCCHI / VIRGO COLLABORATION)

    2.) Adding in a third detector both improves our ability to pinpoint their positions and increases the detection rate significantly. LIGO ran for about 4 months during its first run and 9 months during its second. Yet, fully half of their detections came in the final month: when VIRGO was running alongside it, too. In 2017, gravitational wave events were detected on:

    July 29th (50.6 and 34.3 solar mass black holes),
    August 9th (35.2 and 23.8 solar mass black holes),
    August 14th (30.7 and 25.3 solar mass black holes),
    August 17th (1.46 and 1.27 solar mass neutron stars),
    August 18th (35.5 and 26.8 solar mass black holes), and
    August 23rd (39.6 and 29.4 solar mass black holes).

    During this final month of observing, we were detecting more than one event per week. It’s possible that, as we becomes sensitive to greater distances and smaller-amplitude, lower-mass signals, we may begin seeing as many as one event per day in 2019.

    4
    Cataclysmic events occur throughout the galaxy and across the Universe, from supernovae to active black holes to merging neutron stars and more. When two black holes merge, their peak brightness is enough, for a few short milliseconds, to outshine all the stars in the observable Universe combined. (J. WISE/GEORGIA INSTITUTE OF TECHNOLOGY AND J. REGAN/DUBLIN CITY UNIVERSITY)

    3.) When the black holes we’ve detected collide, they release more energy at their peak than all the stars in the Universe combined. Our Sun is the standard by which we came to understand all other stars. It shines so brightly that its total energy energy output — 4 × 10²⁶ W — is equivalent to converting four million tons of matter into pure energy with every second that goes by.

    With an estimated ~10²³ stars in the observable Universe, the total power output of all the stars shining throughout the sky is greater than 10⁴⁹ W at any given time: a tremendous amount of energy spread out over all of space. But for a brief few milliseconds during the peak of a binary black hole merger, every one of the observed 10 events outshone, in terms of energy, all the stars in the Universe combined. (Although it’s by a relatively small amount.) Unsurprisingly, the most massive merger tops the charts.

    5
    Even though black holes should have accretion disks, there aren’t any significant electromagnetic signals expected to be generated by a black hole-black hole merger. Their energy instead gets converted into gravitational radiation: ripples in the fabric of space itself. We see this radiation, and it’s the most energetic event to occur in the Universe when it happens. (AEI POTSDAM-GOLM)

    4.) About 5% of the total mass of both black holes gets converted into pure energy, via Einstein’s E = mc², during these mergers. The ripples in space that these black hole mergers produce need to get their energy from somewhere, and realistically, that has to come out of the mass of the merging black holes themselves. On average, based on the magnitude of the gravitational wave signals we’ve seen and the reconstructed distances to them, black holes lose about 5% of their total mass — having it converted into gravitational wave energy — when they merge.

    GW170608, the lowest mass black hole merger (of 10.9 and 7.6 solar masses), converted 0.9 solar masses into energy.
    GW150914, the first black hole merger (of 35.6 and 30.6 solar masses), converted 3.1 solar masses into energy.
    And GW170729, the most massive black hole merger (at 50.6 and 34.3 solar masses), converted 4.8 solar masses into energy.

    These events, creating ripples in spacetime, are the most energetic events we know of since the Big Bang. They produce more energy than any neutron star merger, gamma-ray burst, or supernova ever created.

    6
    Illustrated here is the range of Advanced LIGO and its capability of detecting merging black holes. Merging neutron stars may have only one-tenth the range and 0.1% the volume, but we caught one, last year, just 130 million light years away. Additional black holes are likely present and merging, and perhaps run III of LIGO will find them.(LIGO COLLABORATION / AMBER STUVER / RICHARD POWELL / ATLAS OF THE UNIVERSE)

    5.) With everything we’ve seen so far, we fully expect there are lower-mass, more frequent black hole mergers just waiting to be seen. The most massive black hole mergers produce the largest-amplitude signals, and so are the easiest to spot. But with the way volume and distance are related, going twice as distant means encompassing eight times the volume. As LIGO gets more sensitive, it’s easier to spot massive objects at greater distances than low-mass objects that are close by.

    We know there are black holes of 7, 10, 15, and 20 solar masses out there, but it’s easier for LIGO to spot a more massive one farther away. We expect there are black hole binaries with mismatched masses: where one is much more massive than the other. As our sensitivities improve, we expect there are more of these out there to find, but the most massive ones are easier to find. We expect the most massive ones to dominate the early searches, just as “hot Jupiters” dominated early exoplanet searches. As we get better at finding them, expect there to be greater numbers of lower-mass black holes out there.

    7
    LIGO and Virgo have discovered a new population of black holes with masses that are larger than what had been seen before with X-ray studies alone (purple). This plot shows the masses of all ten confident binary black hole mergers detected by LIGO/Virgo (blue). Also shown are neutron stars with known masses (yellow), and the component masses of the binary neutron star merger GW170817 (orange).(LIGO/VIRGO/NORTHWESTERN UNIV./FRANK ELAVSKY)

    When the first gravitational wave detection was announced, it was heralded as the birth of gravitational wave astronomy. People likened it to when Galileo first pointed his telescope at the skies, but it was so much more than that. It was as though our view of the gravitational wave sky had always been shrouded in clouds, and for the first time, we had developed a device to see through them if we got a bright enough gravitational source: merging black holes or neutron stars. The future of gravitational wave astronomy promises to revolutionize our Universe by letting us see it in a whole new way. And that future has already arrived; we are seeing the first fruits of our labor.

    8
    This visualization shows the coalescence of two orbiting neutron stars. The right panel contains a visualization of the matter of the neutron stars. The left panel shows how space-time is distorted near the collisions. For black holes, there is no matter-generated signal expected, but thanks to LIGO and Virgo, we can still see the gravitational waves. (KARAN JANI/GEORGIA TECH)

    As our technology improves, we gain an ever-improved ability to see through those clouds: to see fainter, lower-mass, and more distant gravitational sources. When LIGO starts taking data again in 2019, we fully expect greater rates of ~30 solar mass black holes merging, but we hope to finally know what the lower-mass black holes are doing. We hope to see neutron star-black hole mergers. And we hope to go even farther out into the distant reaches of the Universe.

    Now that we’ve made it into the double digits for the number of detected events, it’s time to go even farther. With LIGO and VIRGO fully operational, and at better sensitivities than ever, we’re ready to go one step deeper in our exploration of the gravitational wave Universe. These merging, massive stellar remnants were just the start. It’s time to visit the stellar graveyard, and find out what the skeletons are truly like.

    See the full article here .

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  • richardmitnick 5:18 pm on December 1, 2016 Permalink | Reply
    Tags: , , MIT Caltech Advanced aLIGO   

    From MIT: “LIGO back online, ready for more discoveries” 

    MIT News

    MIT Widget
    MIT News

    November 30, 2016
    Jennifer Chu

    Upgrades make detectors more sensitive to gravitational waves.

    1
    After making several upgrades, scientists have restarted the twin detectors of LIGO, the Laser Interferometer Gravitational-wave Observatory. The Livingston detector site, located near Livingston, Louisiana, is pictured here. Photo: Caltech/MIT/LIGO Lab

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

    LSC LIGO Scientific Collaboration

    Today, scientists restarted the twin detectors of LIGO, the Laser Interferometer Gravitational-wave Observatory, after making several improvements to the system. Over the last year, they have made enhancements to LIGO’s lasers, electronics, and optics that have increased the observatory’s sensitivity by 10 to 25 percent. The detectors, scientists hope, will now be able to tune in to gravitational waves — and the extreme events from which they arise — that emanate from farther out in the universe.

    On Sept. 14, 2015, LIGO’s detectors made the very first direct detection of gravitational waves, just two days after scientists restarted the observatory as Advanced LIGO — an upgraded version of LIGO’s two large interferometers, one located at Hanford, Washington, and the other 3,000 kilometers away in Livingston, Lousiana. After analyzing the signal, scientists determined that it was indeed a gravitational wave, which arose from the merger of two massive black holes 1.3 billion light years away.

    Three months later, on Dec. 26, 2015, the detectors picked up another signal, which scientists decoded as a second gravitational wave, rippling out from yet another black hole merger, slightly farther out in the universe, 1.4 billion light years away.

    Now with LIGO’s latest upgrades, members of the LIGO Scientific Collaboration are hoping to detect more frequent signals of gravitational waves, arising from colliding black holes and other extreme cosmic phenomena. MIT News spoke with Peter Fritschel, the associate director for LIGO at MIT, and LIGO’s chief detector scientist, about LIGO’s new view.

    Q: What sort of changes have been made to the detectors since they went offline?

    A: There were different sorts of activities at the two observatories. With the detector in Livingston, Louisiana, we did a lot of work inside the vacuum system, replacing or adding new components. As an example, each detector contains four test masses that respond to a passing gravitational wave. These test masses are mounted in complex suspension systems that isolate them from the local environment. Previous testing had shown that two of the vibrational modes of these suspensions could oscillate to a degree that would prevent the detector from operating with its best sensitivity. So, we designed and installed some tuned, passive dampers to reduce the oscillation amplitude of these modes. This will help the Livingston detector operate at its peak sensitivity for a greater fraction of the data run duration.

    On the Hanford, Washington, detector, most of the effort was geared toward increasing the laser power stored in the interferometer. During the first observing run, we had about 100 kilowatts of laser power in each long arm of the interferometer. Since then we worked on increasing this by a factor of two, to achieve 200 kilowatts of power in each arm. This can be quite difficult because there are thermal effects and optical-mechanical interactions that occur as the power is increased, and some of these can produce instabilities that must be tamed. We actually succeeded in solving these types of problems and were able to operate the detector with 200 kilowatts in the arms. However, there were other problems that cost sensitivity, and we didn’t have time to solve these, so we are now operating with 20 to 30 percent higher power than we had in the first observing run. This modest power increase gives a small but noticeable increase in sensitivity to gravitational wave frequencies higher than about 100 hertz.

    We also gathered a lot of important information that will be used to plan out the next detector commissioning period, which will commence at the end of this six-month observation period. We still have a lot of challenging work ahead of us to get to our final design sensitivity.

    Q: How sensitive is LIGO with these new improvements?

    A: The metric we most commonly use is the sensitivity to gravitational waves produced by the merger of two neutron stars, because we can easily calculate what we should see from such a system — but note we have not yet detected gravitational waves from a neutron star-neutron star merger. The Livingston detector is now sensitive enough to detect a merger from as far away as 200 million parsecs (660 million light years). This is about 25 percent farther than it could “see” in the first observing run. For the Hanford detector the corresponding sensitivity range is pretty much on par with what it was during the first run and is about 15 percent lower than these figures.

    Of course in the first observing run we detected the merger of two black holes, not neutron stars. The sensitivity comparison for black hole mergers is nonetheless about the same: Compared to last year’s observing run, the Livingston detector is around 25 percent more sensitive and the Hanford detector is about the same. But even small improvements in sensitivity can help, since the volume of space being probed, and thus the rate of gravitational-wave detections, grows as the cube of these distances.

    Q: What do you hope to “hear” and detect, now that LIGO is back online?

    A: We definitely expect to detect more black hole mergers, which is still a very exciting prospect. Recall that in the first run we detected two such black hole binary mergers and saw strong evidence for a third merger. With the modest improvement in sensitivity and the plan to collect more data than we did before, we should add to our knowledge of the black hole population in the universe.

    We would also love to detect gravitational waves from the merger of two neutron stars. We know these systems exist, but we don’t know how prevalent they are, so we can’t be sure how sensitivity we need to start seeing them. Binary neutron star mergers are interesting because (among other things) they are thought to be the producers and distributers of the heavy elements, such as the precious metals, that exist in our galaxy.

    See the full article here .

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  • richardmitnick 6:38 am on February 20, 2016 Permalink | Reply
    Tags: , , , MIT Caltech Advanced aLIGO,   

    From Space.com: “Here’s How It Felt to Discover Gravitational Waves (Kavli Hangout)” 

    space-dot-com logo

    SPACE.com

    February 19, 2016
    Adam Hadhazy

    Gravitational wave Henze NASA
    Depiction of gravitational waves. NASA Henze

    When Rainer “Rai” Weiss and colleagues first proposed an audacious experiment to detect ripples in [spacetime], called gravitational waves, in the late 1970s, they knew the whole endeavor was a long shot. The waves the researchers sought would pull and stretch their detector by mere billionths of a billionth of a meter — a scarcely believable signal to try to extract from nature.

    Now, four decades later, millions of people worldwide have read about the historic detection of gravitational waves as the result of Weiss and his fellow scientists’ efforts: the Laser Interferometer Gravitational-Wave Observatory (LIGO).

    Caltech Ligo
    MIT/Caltech Advanced aLIGO, Hanford, WA, USA

    The revolutionary gravitational wave findings have thrown open the door to a whole new way of studying the universe’s most extreme events and its most massive objects.

    At the U.S. National Science Foundation’s LIGO announcement in Washington, D.C. last week, Weiss called it “a miracle” that the equations first predicting gravitational waves — which Albert Einstein wrote a century ago — work so well in describing the black hole system LIGO found. “It is just amazing,” he said, adding that he’d “love to be able to see Einstein’s face right now” when the physicist’s name came up in a recent Kavli Foundation roundtable.

    Below is a complete transcript of that roundtable, with Weiss joined by two other LIGO researchers, all members of MIT’s Kavli Institute for Astrophysics and Space Research. Nergis Mavalvala has focused on developing LIGO’s precision instruments (and has become a celebrity scientist in her birthplace of Pakistan since the discovery was announced). Matthew Evans has worked on the modeling and control of large interferometers including LIGO.

    Below, read their far-ranging conversation about the ramifications of LIGO’s discovery and what more is in store in the dawning era of gravitational wave astronomy. The following is an edited transcript of the roundtable discussion. The participants have been provided the opportunity to amend or edit their remarks.

    The Kavli Foundation: What does it feel like to have made this discovery? Rai, because you’re one of LIGO’s creators and someone who has pondered how to detect theses waves since the 1970s, let’s start with you.

    Rai Weiss: You’re not going to like my answer — I feel like a monkey just jumped off my back! But the monkey’s not gone yet, he’s still walking along here on the sidewalk. We’ve got more to do. At least some of the guilty feelings that might have come from having dragged all these people along for decades hunting gravitational waves and maybe ruined their careers isn’t happening. So I am very pleased.

    Matthew Evans: If Rai had dragged us all toward our doom, it certainly would have been his fault. [Laughter] I hope he recognizes that he didn’t.

    Nergis Mavalvala: It’s been a real joyride for decades and this is the pinnacle. It’s been amazing to be involved in the science and technology of this effort regardless, and this discovery just makes it all really worthwhile. I don’t think any of us ever feared we were being dragged to our doom. [Laughter] We were just on this great joyride where we didn’t know where we might end up.

    TKF: This discovery of gravitational waves has been a long time in the making and required a lot of patience. Were you all actually surprised, then, at how quickly the detection was made after Advanced LIGO began operating back in September?

    Mavalvala: Yes.

    Evans: Very pleasantly surprised.

    Weiss: It’s amazing. The signal is bigger than we ever imagined it would be.

    Mavalvala: We had thought the first signal would be some little small thing poking up out of the noise and we’d have to work really hard to understand what it was. But in fact, the signal we got is a very clean and beautiful event. It tells us that the binary black holes were located about 1.5 billion light years away. They whirled around each other at nearly the speed of light before a collision that was so powerful, it converted approximately three times the mass of the Sun into gravitational wave energy — in just a few tenths of a second!

    TKF: Two years ago, the BICEP2 Antarctic telescope project announced evidence for the signature of gravitational waves in light from 380,000 years after the Big Bang.

    BICEP 2
    BICEP 2 interior
    BICEP2

    Gravitational Wave Background
    What BICEP2 saw, which was thought to be evidence of gravitational waves, but which was discredited.

    But that major result came into question in early 2015 when other data suggested cosmic dust is a likelier source of the signature. Do you have any concerns about these LIGO findings?

    Evans: I don’t have any concerns about that. I’ve gone through the instruments from one end to the other and I couldn’t find anything that might have gone wrong. But the LIGO Scientific Collaboration, which is the umbrella organization for all the international institutions and scientists involved in this, is very well aware of the history. So the collaboration as a whole has been extremely careful to make sure this discovery is solid.

    Weiss: The signal is so pretty, many of us worried at the time that it was something done maliciously. Matt and others crucially established that the signal is unlikely to have been generated by a hacker and much more likely by nature.

    Mavalvala: The other possibility was that the instruments were misbehaving, but we’ve gone through a very, very detailed study and eliminated that as a possibility.

    Weiss: There’s one other piece of evidence — LIGO has detected more than one of these gravitational wave signals. That to me is a very important piece of the whole thing. Nature seems to behave as we would have expected, which is that it has produced not only a very powerful gravitational wave source like what we have detected and are talking about now, but also a not-so-powerful one of the same kind.

    Evans: Another thing really important to say in contrast to previously declared discoveries of gravitational waves is that we have multiple detectors running simultaneously which detected the same signal. At each site, we have literally thousands of auxiliary channels and sensors looking for any sort of external disturbance and everything checks out.

    TKF: What do you think are the biggest ramifications of this discovery?

    Weiss: For many of us, this is the signal that we wanted to see from the beginning of this whole quest. We wanted to see gravitation à la Einstein and his theory of general relativity and which cannot be explained by any Newtonian mechanisms. The history of general relativity as a science is actually rather dismal. It was mostly theoretical work for many, many years. Then there was a renaissance in the 1960s when people began to realize that maybe the technology had changed enough that you could start doing experiments to test Einstein’s theories. But then physicists ran into this really horrible problem that all the things that they could test were these infinitesimal effects. The bending of light, for example, is a pipsqueak effect. Or the slowing down of clocks in the gravitational field.

    Now all of sudden with LIGO, we’re dealing with a regime where Einstein’s equations had never been applied before. With these colliding black holes , general relativity gives you the right answer, which is miraculous. That is the reason why this is such a big deal. Einstein never expected this kind of test of his theories to happen this way because the effects we’re looking for are so vanishingly small. I keep telling people I’d love to be able to see Einstein’s face right now!

    Mavalvala: Another thing that’s really remarkable is our ability to observe a binary black hole system with LIGO that we could not have observed with light. We could point the best telescopes, sensitive to more or less any electromagnetic wavelength of light, at this system and probably see nothing. We cannot observe this system with any of the other fundamental forces of nature. It has to be gravity.

    If the signal LIGO had detected had been, say, neutron stars colliding and not black holes, we would have had no complaints, but there’s probably a very good chance you could see neutron star mergers with other, conventional observational tools relying on light. In fact, we believe that certain classes of gamma ray bursts are just that. So what we have here in the findings we’re announcing today is very important, in my opinion, because it’s a completely dark-to-light system.

    Evans: To me, this detection means that the stars are no longer silent. The frequencies of gravitational waves that LIGO is designed to detect are actually in the human audible range. So when we’re working on LIGO, we often take its output and put it on a speaker and just listen to it. For this binary black hole system, it made a distinctive, rising “whoooop!” sound. It’s not that we just look up and see anymore, like we always have — we actually can listen to the universe now. It’s a whole new sense, and humanity did not have this sense until LIGO was built.

    Weiss: We often whistled to demonstrate what we thought these smashing black holes might sound like, and it turns out if you play the piano or a keyboard, you can also make a similar sound. Do you know what a glissando is? It’s when you run your fingers very quickly across the keys. If you started at the bottom of a keyboard and went all the way to the middle C and then hold that note for a little bit — that’s what this black hole signal happened to be.

    TKF: It’s remarkable that the pattern or “sound” of gravitational waves detected by LIGO can reveal intricate details about the waves’ sources. For instance, LIGO’s data indicate that each black hole in this collapsing binary system had a mass of about 30 Suns. Until now, we’ve only known about much smaller black holes or supermassive black holes with masses of millions or billions of Suns. How will LIGO help us understand the origin of these never-before-seen, mid-size black holes?

    Evans: Presumably, the existence of these 30 solar-mass black holes — and now after their collision, a nearly 60-solar mass black hole — will tell us something about what we call Population III stars. These are the earliest stars in the universe and are made almost entirely out of hydrogen. They are very massive and one of the plausible sources we’ve suspected for collapsing into these kinds of black holes.

    Weiss: Another idea is that these black holes are made in places where there is a high density of many millions of stars, for example in globular clusters. You can maybe get stars to stick together there and collect and ultimately make a big black hole. There were papers even before our discovery that were beginning to hint that this is the more likely way to get these objects. Now that our findings are out, you watch — in the next year or two, there are going to be probably hundreds of papers about the origin of the black holes we’re talking about. It’s going to be the wave of the future.

    Evans: The amazing thing at LIGO is that gravitational waves carry a tremendous amount of information about their source. As we get more and more of these detections, we’ll even be able to tell how fast the black holes in these binary systems are spinning and if they are spinning in a way that’s aligned. That data will let us decide whether these black holes came from a globular cluster or as a result of primeval Population III stars.

    Cornell SXS teamTwo merging black holes simulation
    Merging black holes, Cornell

    TKF: Turning our conversation to the LIGO observatories themselves — what technological advances did the black hole binary system discovery hinge on? Nergis, you were very involved in this aspect of the work, so please explain.

    Mavalvala: To build one of these gravitational wave detectors — these laser interferometers — you really only need two ingredients. One, you need mirrors that are very, very still. Then two, you need a way of measuring any very small motions. So the name of the game is having ways to shield mirrors from external, non-gravitational wave forces and having laser lights precise enough that you can probe the tiny motions that are induced by gravitational waves. Once you have those two things, you have yourself a detector.

    The changes that granted us more sensitivity during Advanced LIGO were vibration isolation systems that were better than in the previous generation. In a slightly jargon-y way, we don’t use just passive isolation; we’re also using active vibration isolation. The other thing we had to do was reduce the vibrations of the mirrors due to thermally driven fluctuations. Then finally, we put in a more powerful laser so that our signal-to-noise ratio improved. The list of technologies involved in these improvement is very long, but those are the broad-brush strokes.

    TKF: Matt, part of your work involves figuring out the fundamental limits for LIGO and for future gravitational wave detectors. How much more sensitivity to gravitational waves can we achieve and why do we want to?

    Evans: Putting first things first, we haven’t really gotten the Advanced LIGO detectors working as well as they can be. We will in some time. We think we can get a factor of three times as much sensitivity as we have currently, which could bring ten times as many gravitational wave-producing events into LIGO’s range. So we can expect a lot just from the Advanced LIGO detectors as we improve their function.

    The next step we’re looking at is actually something that Nergis has pioneered, and that’s to use quantum optics in our detectors to reduce the quantum noise of the lights. Nergis talked about having lasers that were very precise and high-powered. But you can actually import techniques from a research field called quantum optics to try to reduce some of the randomness that’s inherent to light. Then, we’re looking farther into the future as to whether or not we can build detectors that are still another ten times more sensitive. That will probably involve a new facility and longer interferometers.

    If you ask why we would want to do that, I think that we’ve just started this business. It looks like we have a lot of great physics and astrophysics we can do with these detectors. If we can make something ten times more sensitive, we’ll be able to detect gravitational wave sources from anywhere in the universe.

    TKF: With an even more advanced LIGO, as well as future gravitational-wave observatories, what other phenomena in the universe will we get to understand in new ways?

    Weiss: There is a whole spectrum of gravitational waves. With LIGO, we’re looking for high-frequency waves. As to how high we can go, again, the piano analogy is a wonderful one. Because what we’re looking for are sources that go from the bottom of the piano to the top of the piano. They don’t stop at middle C, which is currently our detection limit with LIGO. They go higher.

    Beyond that, a lot of people are working in other frequencies and other wavelengths where there are phenomena which LIGO will not see. For example, we talked earlier about the BICEP project, which is looking for signatures of gravitational waves affecting the relic radiation from the Big Bang, called the cosmic microwave background. Well, that’s going to work someday, or it may be that a satellite has to do that observation. If there are gravitational waves from the first epochs of the universe, they’re going to have periods, or cycles, that are stretched to on the order of the age of the universe itself, almost 14 billion years. So that’s the lower limit to the spectrum.

    For another example, there’s a project that’s been going on almost as long as LIGO called the Laser Interferometer Space Antenna Project, or LISA.

    NASA LISA
    ESA/NASA LISA

    It involves lasers beamed between spacecraft with baselines that are up to five million kilometers, not four kilometers, like LIGO’s detection arms now, or even 40 kilometers like what Matt and Nergis want to do someday. LIGO can’t touch LISA’s detection spectrum, covering much longer wavelengths. With LISA, there’s this wide open window with spectacular stuff in it, like binary white dwarf stars going around each other. Another is black holes with tens of thousands to hundreds of thousands of the mass of the Sun, either colliding or having objects bend their orbit around them. You could do very, very careful tests of general relativity with that. I hope these other areas get dragged along by our discovery.

    TKF: Do you think there are any astrophysical objects in our galactic neighborhood that could unleash sizeable gravitational waves detectable by LIGO, or are all the major sources going to be far away?

    Evans: I suggest that we hope that there’s nothing close by. [Laughter] The binary black hole system we detected was 1.5 billion light years distant. That’s very, very far away, and in terms of how much energy was released so quickly, it was the most powerful explosion ever observed. So I think you wouldn’t want that in your neighborhood.

    Mavalvala: But maybe not too close, just within our galaxy…

    Evans: Well, a Milky Way event would probably saturate our detectors, but it’s not like it could hurt us or anything.

    Weiss: Well, I hope you’re right about that! [Laughter] If we ever happen to be around when a supernova goes off, that would be as spectacular as what we have discovered now because we will see everything that is going on deep inside the supernova. Gravitational waves come right out. Nothing scatters these waves, which is the opposite of light that never gets out of the core of the explosion to tell us anything.

    Evans: I hate to get peoples’ hopes up for a supernova because they are so rare, but Rai is absolutely right. If we detect one in our galaxy, it would be a wonderful piece of physics.

    Mavalvala: I’ll add that I hate to get peoples’ hopes up for things we don’t even know how to articulate yet. We don’t fully know what’s out there with this new way of looking at the universe in gravitational waves. So it’s possible that there will be things maybe in our own galactic neighborhood, maybe far away, or maybe both that are just things we have not thought about yet.

    Evans: That’s very true. We’ve heard the loudest possible thing you could imagine go off and we got it, but hey, we’re just getting started.

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  • richardmitnick 8:58 pm on February 19, 2016 Permalink | Reply
    Tags: , , MIT Caltech Advanced aLIGO,   

    From physicsworld.com: “How LIGO will change our view of the universe” 

    physicsworld
    physicsworld.com

    Feb 19, 2016
    Tushna Commissariat

    Gravitational waves
    Gravitational waves, Werner Benger, Zuse-Institut Berlin and Max-Planck-Institut für Gravitationsphysik

    Results and data from the Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO) collaboration – which revealed last week that it had observed a gravitational wave for the first time – are already providing astronomers and cosmologists the world over with previously unknown information about our universe. While the current results have posed intriguing questions for astronomers regarding binary black-hole systems, gravitational-wave astronomy will also revolutionize our understanding of the universe during its infancy, according to cosmologist and Perimeter Institute director Neil Turok.

    Many scientists, such as LIGO veteran Kip Thorne, have pointed out that the collaboration’s results have opened a new window onto the universe. Each time that this has happened in the past, unexpected phenomena have come to light – for example, the advent of radio astronomy revealed the universe’s most luminous objects in the form of quasars and pulsars.

    NRAO VLA
    NRAO/ Very Large Array

    Pristine objects

    Turok told physicsworld.com that black holes – some of the most prolific producers of these ripples – are some of the simplest objects in the universe. He points out that when it comes to these “perfectly pristine objects”, there are “not too many parameters that need to be determined” because a black hole’s dynamics are mainly determined by its mass. Turok also points out that gravitational waves will provide even deeper insights, as they involve the fundamental force of gravity, which itself is still something of a puzzle.

    Indeed, for Turok, this is what is most exciting about aLIGO’s discovery, which he says “may mark a bit of a transition as gravitational-wave observatories become the high-energy colliders of the future as we probe gravity and other extremely basic physics”. Gravitational waves can go to a time/place that, currently, we have very little information about – the early universe, which is opaque to all electromagnetic radiation.

    Looking back in time

    Thankfully, gravitational waves can travel freely through the hot plasma of the early universe and could be used “to look back to a trillionth of a second after the Big Bang”, according to Turok. For him, the discovery is very timely, as he is currently working with colleagues on a new theoretical proposal for “shockwaves” produced a millionth of a second after the Big Bang, which would have been present across all scales in the early universe. If these shockwaves exist, they would have an effect on the measured density variation that is seen in the cosmic microwave background, and could only be detected by gravitational radiation. Once they have a more complete theoretical description, Turok is convinced that LIGO and its successors such as the LISA Pathfinder and other space-based experiments could pick up the shockwave signal, if it exists.

    ESA LISA Pathfinder
    ESA\LISA Pathfinder

    Ultimately, Turok is delighted by LIGO’s discovery, and although he says that it is “much more important than any prize”, he is sure that it will win not only a Nobel prize, but also a slew of others, such as the Breakthrough prize.

    A preprint of Turok’s paper on shockwaves is available on the arXiv server.

    See the full article here .

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  • richardmitnick 9:14 pm on February 18, 2016 Permalink | Reply
    Tags: , , LIGO-India, MIT Caltech Advanced aLIGO   

    From Caltech: “LIGO-India Gets Green Light” 

    Caltech Logo
    Caltech

    02/18/2016
    Kathy Svitil

    Following this month’s announcement of the first observation of gravitational waves arriving at the earth from a cataclysmic event in the distant universe, the Indian Cabinet, chaired by Prime Minister Shri Narendra Modi, has granted in-principle approval to the Laser Interferometer Gravitational-wave Observatory in India (LIGO-India) Project. The project will build an Advanced LIGO Observatory in India, a move that will significantly improve the ability of scientists to pinpoint the sources of gravitational waves and analyze the signals. Approval was granted on February 17, 2016.

    LIGO map
    Current operating facilities in the global network include the twin LIGO detectors—in Hanford, Washington, and Livingston, Louisiana—and GEO600 in Germany. The Virgo detector in Italy and KAGRA in Japan are undergoing upgrades and are expected to begin operations in 2016 and 2018, respectively. A sixth observatory is being planned in India. Having more gravitational-wave observatories around the globe helps scientists pin down the locations and sources of gravitational waves coming from space.
    Credit: LIGO

    Gravitational waves—ripples in the fabric of [spacetime] produced by dramatic events in the universe, such as merging black holes, and predicted as a consequence of Albert Einstein’s 1915 general theory of [general] relativity—carry information about their origins and about the nature of gravity that cannot otherwise be obtained. With their first direct detection, announced on February 11, scientists opened a new window onto the cosmos.

    The twin LIGO Observatories at Hanford, Washington, and Livingston, Louisiana, are funded by the U.S. National Science Foundation (NSF), and were conceived, built, and are operated by Caltech and MIT. Advanced LIGO—a major upgrade to the sensitivity of the instruments compared to the first generation LIGO detectors—began scientific operations in September 2015. Funded in large part by the NSF, Advanced LIGO enabled a large increase in the volume of the universe probed, leading to the discovery of gravitational waves during its first observation run.

    Caltech Ligo
    MIT Caltech Advanced aLIGO

    At each observatory, the two-and-a-half-mile (4-km) long L-shaped interferometer uses laser light split into two beams that travel back and forth down the arms (four-foot diameter tubes kept under a near-perfect vacuum). The beams are used to monitor the distance between mirrors precisely positioned at the ends of the arms. According to Einstein’s theory, the distance between the mirrors will change by an infinitesimal amount when a gravitational wave passes by the detector. A change in the lengths of the arms smaller than one-ten-thousandth the diameter of a proton (10-19 meter) can be detected.

    According to David Reitze, executive director of LIGO and a Caltech research professor, the degree of precision achieved by Advanced LIGO is analogous to being able to measure the distance between our solar system and the sun’s nearest neighbor Alpha Centauri—about 4.4 light-years away—accurately to within a few microns, a tiny fraction of the diameter of a human hair.

    “We have built an exact copy of that instrument that can be used in the LIGO-India Observatory,” says David Shoemaker, leader of the Advanced LIGO Project and director of the MIT LIGO Lab, “ensuring that the new detector can both quickly come up to speed and match the U.S. detector performance.”

    LIGO will provide Indian researchers with the components and training to build and run the new Advanced LIGO detector, which will then be operated by the Indian team.

    According to a statement from the Indian Cabinet, “LIGO-India will also bring considerable opportunities in cutting edge technology for the Indian industry,” which will be responsible for the construction of the new observatory’s 4-kilometer-long beam tubes. In addition, the Cabinet statement says, “The project will motivate Indian students and young scientists to explore newer frontiers of knowledge, and will add further impetus to scientific research in the country.”

    The Indian effort brings together three of the country’s top research institutes; the Inter-University Centre for Astronomy and Astrophysics (IUCAA), the Raja Ramanna Centre for Advanced Technology (RRCAT), and the Institute for Plasma Research (IPR). The project is managed by the Department of Atomic Energy and the Department of Science and Technology.

    “It is technically feasible for LIGO-India to go online by the end of 2023,” says Fred Raab, head of the LIGO Hanford Observatory and LIGO Laboratory liaison for LIGO-India. LIGO scientists have made dozens of trips to India to work with Indian colleagues, especially with the three nodal institutes that would have primary responsibility for construction and operation of LIGO India: IPR Gandhinagar, RRCAT Indore, and IUCAA Pune. “Together, we have identified an excellent site for the facilities and have transferred detailed LIGO drawings of the facilities and vacuum system to IPR, after adapting them for conditions in India,” he says.

    Scientists at RRCAT have designed a special testing/prototype facility for receiving Advanced LIGO parts; have been training the teams that will install and commission the detector; and are currently cross-checking the IPR vacuum-system drawings against the Advanced LIGO detector drawings, to ensure a good fit and rapid installation for the third Advanced LIGO detector. In addition to leading the site-selection process, IUCAA scientists have been setting up a computing center for current and future data. This preparation should make it possible for India to carry the project forward rapidly.

    “LIGO-India will further expand the international network that started with the partnership between LIGO and Virgo, which operates a detector near Pisa, Italy,” says Stanley Whitcomb, LIGO chief scientist. “With LIGO-India added to the network, we will not only detect more sources, we will dramatically increase the number of sources that can be pinpointed so that they can be studied using other types of telescopes.” That ability is pivotal because combining both gravitational-wave and light-based astronomy enables a much more robust understanding of an observed object’s characteristics—in much the same way that lightning is better comprehended through sight and hearing than sight alone.

    “The game to see the light from these catastrophic mergers is on,” says Mansi Kasliwal, assistant professor of astronomy and the leader of the Caltech effort to search for electromagnetic emission from gravitational waves using the intermediate Palomar Transient Factory, a robotic survey for astrophysical transients (brief, intense flashes of light), and a network of other telescopes.

    Palomar Transient Factory I
    Palomar Transient Factory II
    Palomar Transient Factory

    “LIGO India is out of the plane of the other three advanced gravitational-wave interferometers. Thus, it will help narrow down the on-sky location of the gravitational waves tremendously and give a big boost to the astronomers hunting for the light.”

    Indian astronomers have a long tradition of work in general relativity, gravitational waves, the development of algorithms for gravitational wave detection, and also in the data analysis itself, notes Ajit Kembhavi, emeritus professor at IUCAA Pune and chair of the LIGO-India site-selection committee. “The LIGO-India project provides a great opportunity to take these interests forward and to participate in the rapid development of the field, which may very well come to dominate astronomy for some time,” he says.

    “LIGO-India will be able to attract young people with a variety of skills from the numerous students who are engaged in strong programs in STEM education,” adds Somak Raychaudhury, director of IUCAA Pune.

    Fleming Crim, assistant director for mathematical and physical sciences at NSF, praised the expansion of the project, saying, “Because the science reward is so strong, NSF enthusiastically endorses the decision of the Indian government to proceed with authorizing funding for the LIGO-India project.”

    Gabriela González, a professor of physics at Louisiana State University and spokesperson for the LIGO Scientific Collaboration (LSC), says LIGO will “enable us to answer fundamental questions about the universe that no other type of astrophysics or astronomy can answer.” The LSC consists of more than 1000 scientists from more than 90 institutions worldwide, including a large group of researchers in India

    The project may also reveal answers to questions no one has yet thought to ask. Notes Reitze: “Any time you turn on some new type of telescope or microscope, you discover things you couldn’t anticipate. So while there will be certain sources of gravitational waves that we expect to see, the really exciting part is what we did not predict and what we did not expect to see.”

    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 4:36 am on February 12, 2016 Permalink | Reply
    Tags: , , MIT Caltech Advanced aLIGO   

    From LIGO: “Gravitational Waves Detected 100 Years After Einstein’s Prediction” 

    MIT Caltech Caltech Advanced aLigo new bloc

    MIT Caltech Advanced aLIGO

    Cornell SXS teamTwo merging black holes simulation

    Gravitational Waves Detected 100 Years After Einstein’s Prediction

    February 11, 2016

    Caltech
    Kathy Svitil
    Director of News and Content Strategy
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    ksvitil@caltech.edu

    MIT
    Kimberly Allen
    Director of Media Relations
    Deputy Director, MIT News Office
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    allenkc@mit.edu

    NSF
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    Media Officer
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    Virgo
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    GEO
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    Max Planck Institute for Gravitational Physics Hannover
    Benjamin Knispel
    Press Officer
    +49 511 762 19104
    benjamin.knispel@aei.mpg.de

    LIGO Opens New Window on the Universe with Observation of Gravitational Waves from Colliding Black Holes

    WASHINGTON, DC/Cascina, Italy

    For the first time, scientists have observed ripples in the fabric of spacetime called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window onto the cosmos.

    Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained. Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. This collision of two black holes had been predicted but never observed.

    The gravitational waves were detected on September 14, 2015 at 5:51 a.m. Eastern Daylight Time (09:51 UTC) by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA. The LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built, and are operated by Caltech and MIT. The discovery, accepted for publication in the journal Physical Review Letters, was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration and the Australian Consortium for Interferometric Gravitational Astronomy) and the Virgo Collaboration using data from the two LIGO detectors.

    Based on the observed signals, LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the sun, and the event took place 1.3 billion years ago. About 3 times the mass of the sun was converted into gravitational waves in a fraction of a second—with a peak power output about 50 times that of the whole visible universe. By looking at the time of arrival of the signals—the detector in Livingston recorded the event 7 milliseconds before the detector in Hanford—scientists can say that the source was located in the Southern Hemisphere.

    According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final minutes. During the final fraction of a second, the two black holes collide into each other at nearly one-half the speed of light and form a single more massive black hole, converting a portion of the combined black holes’ mass to energy, according to Einstein’s formula E=mc2. This energy is emitted as a final strong burst of gravitational waves. It is these gravitational waves that LIGO has observed.

    The existence of gravitational waves was first demonstrated in the 1970s and 80s by Joseph Taylor, Jr., and colleagues. Taylor and Russell Hulse discovered in 1974 a binary system composed of a pulsar in orbit around a neutron star. Taylor and Joel M. Weisberg in 1982 found that the orbit of the pulsar was slowly shrinking over time because of the release of energy in the form of gravitational waves. For discovering the pulsar and showing that it would make possible this particular gravitational wave measurement, Hulse and Taylor were awarded the Nobel Prize in Physics in 1993.

    The new LIGO discovery is the first observation of gravitational waves themselves, made by measuring the tiny disturbances the waves make to space and time as they pass through the earth.

    “Our observation of gravitational waves accomplishes an ambitious goal set out over 5 decades ago to directly detect this elusive phenomenon and better understand the universe, and, fittingly, fulfills Einstein’s legacy on the 100th anniversary of his general theory of relativity,” says Caltech’s David H. Reitze, executive director of the LIGO Laboratory.

    The discovery was made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first generation LIGO detectors, enabling a large increase in the volume of the universe probed—and the discovery of gravitational waves during its first observation run. The US National Science Foundation leads in financial support for Advanced LIGO. Funding organizations in Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council, STFC) and Australia (Australian Research Council) also have made significant commitments to the project. Several of the key technologies that made Advanced LIGO so much more sensitive have been developed and tested by the German UK GEO collaboration. Significant computer resources have been contributed by the AEI Hannover Atlas Cluster, the LIGO Laboratory, Syracuse University, and the University of Wisconsin- Milwaukee. Several universities designed, built, and tested key components for Advanced LIGO: The Australian National University, the University of Adelaide, the University of Florida, Stanford University, Columbia University of the City of New York, and Louisiana State University.

    “In 1992, when LIGO’s initial funding was approved, it represented the biggest investment the NSF had ever made,” says France Córdova, NSF director. “It was a big risk. But the National Science Foundation is the agency that takes these kinds of risks. We support fundamental science and engineering at a point in the road to discovery where that path is anything but clear. We fund trailblazers. It’s why the U.S. continues to be a global leader in advancing knowledge.”

    LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of more than 1000 scientists from universities around the United States and in 14 other countries. More than 90 universities and research institutes in the LSC develop detector technology and analyze data; approximately 250 students are strong contributing members of the collaboration. The LSC detector network includes the LIGO interferometers and the GEO600 detector. The GEO team includes scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI), Leibniz Universität Hannover, along with partners at the University of Glasgow, Cardiff University, the University of Birmingham, other universities in the United Kingdom, and the University of the Balearic Islands in Spain.

    “This detection is the beginning of a new era: The field of gravitational wave astronomy is now a reality,” says Gabriela González, LSC spokesperson and professor of physics and astronomy at Louisiana State University.

    LIGO was originally proposed as a means of detecting these gravitational waves in the 1980s by Rainer Weiss, professor of physics, emeritus, from MIT; Kip Thorne, Caltech’s Richard P. Feynman Professor of Theoretical Physics, emeritus; and Ronald Drever, professor of physics, emeritus, also from Caltech.

    “The description of this observation is beautifully described in the Einstein theory of general relativity formulated 100 years ago and comprises the first test of the theory in strong gravitation. It would have been wonderful to watch Einstein’s face had we been able to tell him,” says Weiss.

    “With this discovery, we humans are embarking on a marvelous new quest: the quest to explore the warped side of the universe—objects and phenomena that are made from warped spacetime. Colliding black holes and gravitational waves are our first beautiful examples,” says Thorne.

    Virgo research is carried out by the Virgo Collaboration, consisting of more than 250 physicists and engineers belonging to 19 different European research groups: 6 from Centre National de la Recherche Scientifique (CNRS) in France; 8 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; 2 in The Netherlands with Nikhef; the Wigner RCP in Hungary; the POLGRAW group in Poland; and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy.

    Fulvio Ricci, Virgo Spokesperson, notes that, “This is a significant milestone for physics, but more importantly merely the start of many new and exciting astrophysical discoveries to come with LIGO and Virgo.”

    Bruce Allen, managing director of the Max Planck Institute for Gravitational Physics (Albert Einstein Institute), adds, “Einstein thought gravitational waves were too weak to detect, and didn’t believe in black holes. But I don’t think he’d have minded being wrong!”

    “The Advanced LIGO detectors are a tour de force of science and technology, made possible by a truly exceptional international team of technicians, engineers, and scientists,” says David Shoemaker of MIT, the project leader for Advanced LIGO. “We are very proud that we finished this NSF-funded project on time and on budget.”

    At each observatory, the two-and-a-half-mile (4-km) long L-shaped LIGO interferometer uses laser light split into two beams that travel back and forth down the arms (four-foot diameter tubes kept under a near-perfect vacuum). The beams are used to monitor the distance between mirrors precisely positioned at the ends of the arms. According to Einstein’s theory, the distance between the mirrors will change by an infinitesimal amount when a gravitational wave passes by the detector. A change in the lengths of the arms smaller than one-ten-thousandth the diameter of a proton (10-19 meter) can be detected.

    “To make this fantastic milestone possible took a global collaboration of scientists—laser and suspension technology developed for our GEO600 detector was used to help make Advanced LIGO the most sophisticated gravitational wave detector ever created,” says Sheila Rowan, professor of physics and astronomy at the University of Glasgow.

    Independent and widely separated observatories are necessary to determine the direction of the event causing the gravitational waves, and also to verify that the signals come from space and are not from some other local phenomenon.

    Toward this end, the LIGO Laboratory is working closely with scientists in India at the Inter-University Centre for Astronomy and Astrophysics, the Raja Ramanna Centre for Advanced Technology, and the Institute for Plasma to establish a third Advanced LIGO detector on the Indian subcontinent. Awaiting approval by the government of India, it could be operational early in the next decade. The additional detector will greatly improve the ability of the global detector network to localize gravitational-wave sources.

    “Hopefully this first observation will accelerate the construction of a global network of detectors to enable accurate source location in the era of multi-messenger astronomy,” says David McClelland, professor of physics and director of the Centre for Gravitational Physics at the Australian National University.

    Additional video and image assets can be found here: http://mediaassets.caltech.edu/gwave

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    LIGO Hanford Observatory

     
  • richardmitnick 3:33 pm on February 10, 2016 Permalink | Reply
    Tags: , , , MIT Caltech Advanced aLIGO,   

    From Ethan Siegel via Forbes: “What Will It Mean If LIGO Detects Gravitational Waves?” 

    ForbesMag

    Forbes Magazine

    Starts with a bang
    Starts with a Bang

    Feb 9, 2016
    Ethan Siegel

    Cornell SXS teamTwo merging black holes simulation
    Image credit: Bohn et al 2015, SXS team, of two merging black holes and how they alter the appearance of the background spacetime in General Relativity.

    For over a decade, to very little fanfare, a new type of astronomy has been going on: gravitational wave astronomy. Rather than using a telescope to look out at the Universe, a gravitational wave detector uses lasers, fired and reflected perpendicular to one another, and then reconstructed to create a specific interference pattern when they’re reunited. This apparatus — the Laser Interferometer Gravitational-Wave Observatory (LIGO) — demonstrated its proof-of-concept from 2002-2010, and then was shut down for five years while it was upgraded.

    Caltech Ligo
    MIT/Caltech Advanced aLIGO

    In September of 2015, it was turned back on with the new upgrade (Advanced LIGO), and in just two days, the Advanced LIGO collaboration is going to make their first major announcement, and the speculation is this: that they’re going to announce the direct detection of the first gravitational wave. Here’s what that would mean.

    When [Albert] Einstein’s General Relativity was first proposed, it was incredibly different from the concept of space and time that came before. Rather than being fixed, unchanging quantities that matter and energy traveled through, they are dependent quantities: dependent on one another, dependent on the matter and energy within them, and changeable over time. If all you have is a single mass, stationary in spacetime (or moving without any acceleration), your spacetime doesn’t change. But if you add a second mass, those two masses will move relative to one another, will accelerate one another, and will change the structure of your spacetime. In particular, because you have a massive particle moving through a gravitational field, the properties of General Relativity mean that your mass will get accelerated, and will emit a new type of radiation: gravitational radiation.

    pulsar orbiting a binary companion and the gravitational waves (or ripples) in spacetime that ensue as a resul ESO
    Image credit: ESO/L. Calçada, of a pulsar orbiting a binary companion and the gravitational waves (or ripples) in spacetime that ensue as a result.

    This gravitational radiation is unlike any other type of radiation we know. Sure, it travels through space at the speed of light, but it itself is a ripple in the fabric of space. It carries energy away from the accelerating masses, meaning that if the two masses orbit one another, that orbit will decay over time. And it’s that gravitational radiation — the waves that cause ripples through space — that carries the energy away. For a system like the Earth orbiting the Sun, the masses are so (relatively) small and the distances so large that the system will take more than 10^150 years to decay, or many, many times the current age of the Universe. (And many times the lifetime of even the longest-lived stars that are theoretically possible!) But for black holes or neutron stars that orbit each other, those orbital decays have already been observed.

    Neutron stars merging
    Image credit: NASA (L), Max Planck Institute for Radio Astronomy / Michael Kramer, via http://www.mpg.de/7644757/W002_Physics-Astronomy_048-055.pdf.

    We suspect there are even stronger systems out there that we simply haven’t been able to detect, like black holes that spiral into and merge with one another. These should exhibit characteristic signals, like an inspiral phase, a merger phase, and then a ringdown phase, all of which result in the emission of gravitational waves that Advanced LIGO should be able to detect. The way the Advanced LIGO system works is nothing short of brilliant, and it takes advantage of the unique radiation of these gravitational waves. In particular, it takes advantage of how they cause spacetime to respond.

    These ripples work by compressing and then expanding space in directions that are perpendicular to one another, with frequencies and intensities that are dependent on a number of properties of where they come from, such as the two masses that spiral into one another, their distance from one another, and their distance from us. Advanced LIGO shoots two lasers of identical frequencies/wavelengths perpendicular to one another down a shaft four kilometers in either direction, bounces them off of mirrors many times over (effectively increasing the path-length to thousands of kilometers), and then brings them back together, where they create an interference pattern with one another.

    MIT Caltech Advanced aLIGO how it works schematic
    Image credit: public domain / US Government, of a schematic of how LIGO works. Modifications made by Krzysztof Zajączkowski.

    Under normal circumstances (where no gravitational waves pass through them), these path lengths are equal, and the interference pattern looks normal. But if a gravitational wave does pass through, that interference pattern will shift in a particular set of circumstances, and that shift will tell us the mass of each part of the system, how far apart they are and how distant they are from us.

    We have two Advanced LIGO system set up: one in the northwest United States (in Washington) and one in the southeast United States (in Louisiana), and if both detectors see the same thing, we’ll catch our first gravitational wave! This version of LIGO should be most sensitive to two black holes between 1 and a few hundred solar masses merging together out to many millions of light years: something that’s expected to happen at least a few times a year.

    Advanced aLIGO search range MIT Caltech
    Image credit: Caltech/MIT/LIGO Lab, of the Advanced LIGO search range.

    If the collaboration does announce their first detected event this Thursday, they’ll not only have this information for us, it will be a brand new successful test of Einstein’s General Relativity, and the first direct evidence for gravitational radiation ever. Advanced LIGO is the most advanced gravitational wave observatory ever constructed, and the first one that ought to actually see a true signal. With nearly 1,000 scientists on board, it’s the largest scientific collaboration designed to search for them as well. If all goes as suspected, a new era of astronomy is about to begin.

    MIT Caltech Advanced aLIGO Installing Upgrades
    Installing the Advanced LIGO upgrades. Image credit: Caltech/MIT/LIGO Lab, taken by Cheryl Vorvik.

    I’m very much against doing science by rumor. But if they find a gravitational wave, this is what it’ll teach us: that Einstein’s relativity is right, that gravitational radiation is real, and that merging black holes not only produce them, but that these waves can be detected. It’s a whole new type of astronomy — one that doesn’t use telescopes — and a whole new way to view black holes, neutron stars, and other objects that are otherwise mostly invisible. For the first time, we may be developing eyes for examining the Universe in a way that no living creature has ever examined it before.

    See the full article here .

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

     
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