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Sound of the cosmos

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

 

 

The “chirp” is bright and bird-like, its pitch rising at the end as though it’s asking a question. To an untrained ear, it resembles a sound effect from a video game more than the faint, billion-year-old echo of the collision of two black holes.

From Aristotle to Einstein, the world’s greatest minds have long theorized about gravity. Here are the highlights, and where the study of gravity is headed next. (Gillian Brockell,Joel Achenbach/TWP)

https://www.washingtonpost.com/news/morning-mix/wp/2016/02/12/einstein-predicted-gravitational-waves-100-years-ago-heres-what-it-took-to-prove-him-right/

 

But to the trained ear of experimental physicist, it is the opening note of a cosmic symphony. On Thursday, for the first time in history, scientists announced that they are able to hear the ripples in the space-time continuum that are produced by cosmic events — called gravitational waves. The discovery opens up a new field of scientific research, one in which physicists listen for the secrets of the universe rather than looking for them.

[Everything you need to know about gravitation waves (in gifs)]

“Until this moment, we had our eyes on the sky and we couldn’t hear the music,” said Columbia University astrophysicist Szabolcs Márka, a member of the discovery team, according to the Associated Press. “The skies will never be the same.”

 

Scientists from the Laser Interferometer Gravitational-wave Observatory (LIGO) announced on Feb. 11 that they have detected gravitational waves, ushering in a new era in the way humans can observe the universe. (Reuters)

 

Thursday’s moment of revelation has its roots a century earlier, in 1916, when Albert Einstein predicted the existence of gravitational waves as part of his ground-breaking theory of general relativity. The intervening years included brush-offs and boondoggles, false hope, reversals of opinion, an unlikely decision to take a $272 million risk, and a flash of serendipity that seemed too miraculous to be real — but wasn’t.

Here’s how it all happened.

[LIGO’s success was built on many failures]

In 1915, Einstein gave a series of lectures on his General Theory of Relativity, asserting that space and time form a continuum that gets distorted by anything with mass. The effect of that warping is gravity — the force that compels everything, from light to planets to apples dropping from a tree, to follow a curved path through space.

Gravitational waves, which he proposed the following year, are something of a corollary to that theory. If spacetime is the fabric of the cosmos, then huge events in the cosmos — like a pair of black holes banging into each other — must send ripples through it, the way the fabric of a trampoline would vibrate if you bounced two bowling balls onto it. Those ripples are gravitational waves, and they’re all around us, causing time and space to minutely squeeze and expand without us ever noticing. They’re so weak as to be almost undetectable, and yet, according to Einstein’s math at least, they must be there.

But like the entire theory of general relativity, gravitational waves were just a thought experiment, just equations on paper, still unproven by real-world events. And both were controversial. Some people believe that the initial skepticism about Einstein’s theory, plus blatant anti-Semitism — some prominent German physicists called it “world-bluffing Jewish physics,” according to Discover Magazine — explain why he never got the Nobel Prize for it. (He was eventually awarded the the 1921 Nobel Prize in Physics for his explanation of the photoelectric effect.)

A century after Einstein hypothesized that gravitational waves may exist, scientists who have been trying to track such waves are gearing up for a news conference. (Reuters)

 

So scientists came up with a series of tests of general relativity. The biggest took place in 1919, when British physicist Sir Arthur Eddington took advantage of a solar eclipse to see if light from stars bent as it made its way around the sun (as Einstein said it should). It did, surprising Einstein not in the slightest.

According to Cosmos, when he was asked what he would have done if the measurements had discredited his theory, the famous physicist replied: “In that case, I would have to feel sorry for God, because the theory is correct.”

[Inside LIGO: Physicists detect gravitational waves]

One by one, successive experiments proved other aspects of general relativity to be true, until all but one were validated. No one, not even Einstein, could find evidence of gravitational waves. Eddington, who so enthusiastically demonstrated Einstein’s theory of relativity, declared that gravitational waves were a mathematical phantom, rather than a physical phenomenon. The only attribute the waves seemed to have, he snidely remarked, was the ability to travel “at the speed of thought.” In the end, Einstein himself had doubts. Twice he reversed himself and declared that gravitational waves were nonexistent, before turning another about-face and concluding that they were real.

 

A small statue of Albert Einstein is seen at the Einstein Archives of Hebrew University in Jerusalem on Feb. 11, 2016, during presentation of the original 100-year-old documents of Einstein’s prediction of the existence of gravitational waves.(Abir Sultan/EPA)

 

Time passed. A global depression happened, followed by a global war. A reeling and then resurgent world turned its scientific eye toward other prizes: bombs, rockets, a polio vaccine. Then, in the 1960s, an engineering professor at the University of Maryland decided he would try his hand at capturing the waves that had so eluded the man who first conceived of them.

The engineer, Joe Weber, set up two aluminum cylinders in vacuums in labs in Maryland and Chicago. The tiny ripples of gravitational waves would cause the bars to ring like a bell, he reasoned, and if both bars rang at once, then he must have found something.

Weber declared his first discovery in 1969, according to the New Yorker. The news was met with celebration, then skepticism, as other laboratories around the country failed to replicate his experiment. Weber never gave up on his project, continuing to claim new detections until he died in 2000. But others did. It didn’t help that gravitational waves supposedly detected by a South Pole telescope in 2014 turned out to be merely a product of cosmic dust.

People were inclined to believe, physicist Rainer Weiss told the New Yorker, that gravitational-wave hunters were “all liars and not careful, and God knows what.”

[A brief history of gravity, gravitational waves and LIGO]

Weiss would prove them wrong. Now 83, he was a professor at the Massachusetts Institute of Technology when Weber first started publishing his purported discoveries.

“I couldn’t for the life of me understand the thing he was doing,” he said in aQ&A for the university website. “That was my quandary at the time, and that’s when the invention was made.”

Weiss tried to think of the simplest way to explain to his students how gravitational waves might be detected, and came up with this: Build an immense, L-shaped tunnel with each leg an equal length and a mirror at the far ends, then install two lasers in the crook of the L. The beams of light should travel down the tunnels, bounce off the mirrors, and return to their origin at the same time. But if a gravitational wave was passing through, spacetime would be slightly distorted, and one light beam would arrive before the other. If you then measure that discrepancy, you can figure out the shape of the wave, then play it back as audio. Suddenly, you’re listening to a recording of the universe.

That idea would eventually become the Laser Interferometer Gravitational-Wave Observatory (LIGO), the pair of colossal facilities in Washington and Louisiana where the discovery announced Thursday was made.

 

But not without overcoming quite a few obstacles.

For one thing, even though gravitational waves are all around us, only the most profound events in the universe produce ripples dramatic enough to be measurable on Earth — and even those are very, very faint. For another, an instrument of the size and strength that Weiss desired would require a host of innovations that hadn’t even been created yet: state-of-the-art mirrors, advanced lasers, supremely powerful vacuums, a way to isolate the instruments from even the faintest outside interference that was better than anything that had existed before. The L tunnel would also have to be long — we’re talking miles here — in order for the misalignment of the light beams to be detectable. Building this instrument was not going to be easy, and it was not going to be cheap.

And there would need to be two of them. The principles of good scientific inquiry, which requires that results be duplicated, demanded it.

It took a few decades and a number of proposals, but in 1990 the National Science Foundation finally bit. Weiss and his colleagues could have $272 million for their research.

“It should never have been built,” Rich Isaacson, a program officer at the National Science Foundation at the time, told the New Yorker. “There was every reason to imagine [LIGO] was going to fail,” he also said.

But it didn’t. Twenty-one years and several upgrades after ground was broken on the first LIGO lab, the instruments finally found something on Sept. 14, 2015.

Like most scientific discoveries, this one started not with a “Eureka,” but a “Huh, that’s weird.”

That’s what Marco Drago, a soft-spoken post-doc sitting at a desk in Hanover, Germany, thought when he saw an email pop up in his inbox. It was from a computer program that sorts through data from LIGO to detect evidence of gravitational waves. Drago gets those messages almost daily, he told Science Magazine — anytime the program picks up an interesting-seeming signal.

This was a big one. Almost too big, considering that Sept. 14 was the very first day of official observations for the newly revamped LIGO instruments. Drago could only assume that the pronounced blip in his data was a “blind injection,” an artificial signal introduced to the system to keep researchers on their toes, make sure that they’re able to treat an apparently exciting development with the appropriate amount of scrutiny.

But the injection system wasn’t supposed to be running yet, since research had just started. After about an hour of seeking some other explanation, Drago sent an email to the whole LIGO collaboration, he told Science: Was there an injection today? No, said an email sent that afternoon. Something else must have caused it.

But no one had an explanation for the signal. Unless, of course, it was what they were looking for all along.

https://img.washingtonpost.com/wp-apps/imrs.php?src=https://img.washingtonpost.com/rf/image_908w/2010-2019/WashingtonPost/2016/02/11/Health-Environment-Science/Images/2016-02-11T191817Z_01_TOR351_RTRIDSP_3_SPACE-GRAVITYWAVES.jpg&w=1484

An aerial photo shows Laser Interferometer Gravitational-Wave Observatory (LIGO) Hanford laboratory detector site near Hanford, Washington in this undated photo released by Caltech/MIT/LIGO Laboratory on Feb. 8, 2016. (Caltech/MIT/LIGO Laboratory/Handout via Reuters)

Chad Hanna, an assistant professor of physics at Pennsylvania State University who was also part of the LIGO team, blanched as he read the successive emails about the weird signal. He and his colleagues had joked about their instruments detecting something on Day One, he wrote for the Conversation, but no one imagined that it could really happen.

“My reaction was, ‘Wow!’” LIGO executive director David Reitze said Thursday, as he recalled seeing the data for the first time. “I couldn’t believe it.”

Yet, as the weeks wore on and after an exhaustive battery of tests — including an investigation to make sure that the signal wasn’t the product of some ill-conceived prank or hoax — all the other possible sources of the signal were rejected. Only one remained: Long ago and far from Earth, a pair of black holes began spiraling around one another, getting closer and closer, moving faster and faster, whirling the spacetime around them, until, suddenly, they collided. A billion years later, a ripple from that dramatic collision passed through the two LIGO facilities, first in Louisiana, then, after 7 milliseconds, in Washington.

The realization of what they’d found hit the LIGO collaborators differently. For some, it was a vindication — for themselves as well as the men who inspired them: “Einstein would be beaming,” Kip Thorne, a Cal-Tech astrophysicist and co-founder of the project with Weiss, said at the news conference Thursday.

After the briefing, he also credited Weber, the UMD professor: “It does validate Weber in a way that’s significant. He was the only person in that era who thought that this could be possible.”

Thorne told Scientific American that he’s feeling a sense of “profound satisfaction” about the discovery. “I knew today would come and it finally did,” he said.

For Weiss, who had invested half his life in the search for gravitational waves, there’s just an overpowering sense of relief.

“There’s a monkey that’s been sitting on my shoulder for 40 years, and he’s been nattering in my ear and saying, ‘Ehhh, how do you know this is really going to work? You’ve gotten a whole bunch of people involved. Suppose it never works right?’” he told MIT. “And suddenly, he’s jumped off.”

But the mood Thursday was mostly one of awe, and joy, and excitement to see what comes next.

Neil deGrasse Tyson, director of the Hayden Planetarium at the American Museum of Natural History and celebrity astrophysicist, joined a gathering of Columbia University scientists who had been involved in the LIGO project. They cheered as they watched the Washington, D.C., news conference where Reitze announced the find.

“One hundred years feels like a lifetime, but over the course of scientific exploration it’s not that long,” Tyson told Scientific American about the long search for gravitational waves. “I lay awake at night wondering what brilliant thoughts people have today that will take 100 years to reveal themselves.”

 

Gravitational Waves Detected 100 Years After Einstein’s Prediction

LIGO Caltech

http://www.scientificcomputing.com/news/2016/02/gravitational-waves-detected-100-years-after-einsteins-prediction

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, LA, and Hanford, WA.

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 three 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 seven 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 five 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 U.S. 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: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two 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 (four-kilometer) 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.

 

‘The Universe Has Spoken to Us’, Gravitational Waves Discovered

Greg Watry, Digital Reporter   http://www.rdmag.com/articles/2016/02/universe-has-spoken-us-gravitational-waves-discovered

An aerial view of the Laser Interferometer Gravitational-wave Observatory (LIGO) detector in Livingston, Louisiana. LIGO has two detectors: one in Livingston and the other in Hanaford, Washington. LIGO is funded by NSF; Caltech and MIT conceived, built and operate the laboratories. Credit: LIGO Laboratory

The National Science Foundation announced that scientists have officially detected ripples in spacetime, 100 years after Albert Einstein predicted the existence of such phenomena.

“Ladies and gentlemen, we have detected gravitational waves,” said Laser Interferometer Gravitational-wave Observatory (LIGO) Executive Director David Reitze at a press conference hosted today in Washington, D.C.

On Sept. 14, 2015, both LIGO detectors detected gravitational waves emanating from the merging of two black holes. These black holes, which each stuff about 30 solar masses in a space a little over 150 km in diameter, circled one another 1.3 billion years ago. As they approached each other, they increased in acceleration and warped the surrounding space before coalescing into a single black hole at about half the speed of light. The collision sent a ripple emanating outwards into the universe.

“This is the first time that this kind of system has ever been seen,” said Reitze. “It’s proof that binary black holes exist in the universe.”

The study behind the discovery was accepted for publication in Physical Review Letters.

The signal picked up by LIGO was detected by the detector in Livingston, La. about seven milliseconds before it was detected by the Hanford, Wash. counterpart.

“It’s the first time the universe has spoken to us through gravitational waves,” said Reitze. “We were deaf to them” before.

The LIGO detectors, operated by the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT), are designed to detect the most diminutive disturbances in spacetime. The detectors, which are L-shaped and about 4 km long, shoot laser beams, which are split into two, down the length of their arms. Mirrors positioned at the end of the arms are monitored by the beams. A gravitational wave is capable of changing the distance between the mirrors, and LIGO can detect changes down to one-ten-thousandth the diameter of a proton.

“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,” said the project’s leader David Shoemaker, of MIT.

Reitze said the discovery is on par with Galileo Galilei’s breakthrough with observational astronomy, and will change the way we look at the universe. It introduces to the world of science the field of gravitational wave astronomy.

 

updated 2/15/2016

http://www.kurzweilai.net/images/black-holes-merging.jpg

Numerical simulations of the gravitational waves emitted by the inspiral and merger of two black holes. The colored contours around each black hole represent the amplitude of the gravitational radiation; the blue lines represent the orbits of the black holes and the green arrows represent their spins. (credit: C. Henze/NASA Ames Research Center)

 

On Sept. 14, 2015 at 5:51 a.m. EDT (09:51 UTC) for the first time, scientists observed ripples in the fabric of spacetime called gravitational waves, arriving at Earth from a cataclysmic event in the distant universe, the National Science Foundation and scientists at the LIGO Scientific Collaboration announced today. This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window to the cosmos.

Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot be obtained from elsewhere. 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.

http://www.kurzweilai.net/images/proof.jpg

The gravitational-wave event on Sept. 14, 2015 at 09:50:45 UTC was observed by the two LIGO detectors in Livingston, Loiusiana (blue) and Hanford, Washington (orange). The matching waveforms represent gravitational-wave strain inferred to be generated by the merger of two inspiraling black holes. (credit: B. P. Abbott et al./PhysRevLett)

 

The gravitational waves were detected  by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington. The LIGO observatories are funded by the National Science Foundation (NSF), and were conceived, built and are operated by the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (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.

The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10⁻²¹.

 

http://www.kurzweilai.net/images/black-holes-simulation.jpg

Illustration of the collision of two black holes — an event detected for the first time ever by the Laser Interferometer Gravitational-Wave Observatory, or LIGO — is seen in this still from a computer simulation. LIGO detected gravitational waves, or ripples in space and time, generated as the black holes merged. (credit: SXS)

 

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 three 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 at nearly 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. These are the gravitational waves that LIGO observed.

 

How our sun and Earth warp spacetime is represented here with a green grid. As Albert Einstein demonstrated in his theory of general relativity, the gravity of massive bodies warps the fabric of space and time — and those bodies move along paths determined by this geometry. His theory also predicted the existence of gravitational waves, which are ripples in space and time. These waves, which move at the speed of light, are created when massive bodies accelerate through space and time. (credit: T. Pyle/LIGO)

 

The existence of gravitational waves was first demonstrated in the 1970s and 1980s by Joseph Taylor, Jr., and colleagues. In 1974, Taylor and Russell Hulse discovered 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 1993 Nobel Prize in Physics.

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 five 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.

 

http://www.kurzweilai.net/images/LIGO-Observatory.jpg

An aerial view of the Laser Interferometer Gravitational-wave Observatory (LIGO) detector in Livingston, Louisiana. LIGO has two detectors: one in Livingston and the other in Hanford, Washington. (credit: LIGO Laboratory)

 

LIGO research

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. NSF is the lead financial supporter of 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.

LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of more than 1,000 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 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: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two 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.

At each observatory, the 2 1/2-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.

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.

The finding is described in an open-access paper in Physical Review Letters today (Feb. 11).

 

https://youtu.be/aEPIwEJmZyE

Observation of Gravitational Waves from a Binary Black Hole Merger

B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration)

Phys. Rev. Lett. 116, 061102 – Published 11 February 2016

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10−21. It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203 000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410+160−180  Mpc corresponding to a redshift z=0.09+0.03−0.04. In the source frame, the initial black hole masses are 36+5−4M⊙ and 29+4−4M⊙, and the final black hole mass is 62+4−4M⊙, with 3.0+0.5−0.5M⊙c2radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

 

See Viewpoint: The First Sounds of Merging Black Holes

 

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