Gravitational Waves Found in 1.3 Billion Year Old Black Hole Collision
It happened faster than anyone expected.
Last September, physicists started recording data from the new Advanced LIGO detectors, a pair of ultra-precise observatories waiting for the slightest perturbation that could suggest the existence of gravitational waves, the ripples in spacetime predicted by Einstein almost exactly 100 years ago. Then, after just 16 days, they found it.
The team spent the next several months double checking every angle to make sure that this was, in fact, the result they were looking for. It was.
"Ladies and gentlemen, we have detected gravitational waves," said David Reitze, executive director of LIGO Laboratory, in a press conference this morning. "We did it."
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Scientists have discovered gravitational waves emanating from the merger of two black holes.
Advanced LIGO is a set of upgrades to of LIGO, the Laser Interferometer Gravitational-Wave Observatory, which is located in both Livingston, Louisiana and the other Hanford, Washington. The two outposts of the observatory both confirmed the result.
"The sensitivity of the Advanced LIGO is about four times greater than LIGO," said Greg Kestin, a physicist at Harvard University and producer of What the Physics. "It's not surprising with this version that they've seen something that we might have seen earlier but missed. The magnitude that you'd expect from black holes colliding is on the order of magnitude of what they can measure now.
"I'd have been more surprised if they didn't find anything eventually," Kestin said. "I'm surprised they found it so quickly."
The result landed in the form of a half-second thump—quite literally something that went bump in the darkness of space. Though it was brief, it was unambiguously caused by gravitational waves, likely from the collision of two orbiting black holes some 1.3 billion light-years away.
"I guess you could say we observed three black holes, two to begin with and one at the end," said Matthew Evans, an assistant professor of physics at MIT and a LIGO collaborator.
Physicists are in such new territory that they're having a difficult time ascribing a precise significance to the results, the standard by which their data is measured. "This results is at at least 5.1 sigma. And I emphasize at least, because all we can really do is set a limit on the significance," Evans said. "There was nothing in the background that looked anything like these events."
The two black holes were medium-sized but still the largest ever observed—29 and 36 solar masses. It is also the first time astronomers have witnessed the merger of a black hole.
Though the team didn't witness the merger with any other observatory, they're confident in their conclusion because it matches the prediction made by calculations supported by general relativity. The results are published in the journal Physical Review Letters.
The discovery of gravitational waves gives scientists an entirely new way of looking at the universe. "As we open a new window into astronomy, we may see things we've never seen before," Reitze said.
Discover how the LIGO team detected gravitational waves in our exclusive feature article, and listen to the sound of two black holes colliding over at PRI's "The World."
http://www.pbs.org/wgbh/nova/next/physics/gravitational-waves-discovered
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How LIGO Detected Gravitational Waves
For 13 years, the scientists of LIGO—the most ambitious, and expensive, project in the history of the National Science Foundation—had been waiting.
LIGO, the Laser Interferometer Gravitational-Wave Observatory, has been twenty-five years and more than half a billion dollars in the making. It involves 900 scientists and engineers, including many whose entire careers have been spent designing, building, and preparing to analyze data streaming in to LIGO. Their goal: To confirm, once and for all, Einstein's century-old idea that gravity travels across space-time in the form of gravitational waves.
Well, they did.
This morning, the LIGO team announced that they had picked up gravitational waves from the collision of two orbiting black holes. "We have detected gravitational waves from a binary black hole system," says Matthew Evans, an assistant professor of physics at MIT and a LIGO collaborator. "They're the largest stellar mass black holes we've ever observed, and the first time we've observed such things merging together."
(http://www.pbs.org/wgbh/nova/next/wp-content/uploads/2016/02/gravitational-waves.jpeg)
gravitational-waves
A visualization of two black holes merging based on general relativity's predictions.
The collision landed on the detectors like a half-second thump—somewhat literally. "I would say heard more than saw in the sense that gravitational waves signal is much more like audio signal than a video signal," Evans says. "We can literally put the signal on a speaker and listen to it."
It sounds like a happy ending, but in reality, this first detection is just the beginning of a brand new way of looking at the universe, one that will pull back the covers on some of the most extreme events in the universe, like black hole collisions and supernova explosions. We've been blind—but we're about to see a lot more.
A New Way of Seeing
For the entire history of civilization, we've explored the universe in just one way, using light—that is, electromagnetic waves. "Everything that you and I know about the universe—every time we see a picture on the web, or in the news—it has been something that's been learned with light," says Shane Larson, a gravitational wave researcher at Northwestern University's Center for Interdisciplinary Exploration and Research in Astrophysics.
For millennia, humans have used visible light, the kind that you can see with your naked eyes, to learn about the cosmos. In the last century or so, we've expanded that view, building telescopes that can see infrared, ultraviolet, radio, X-rays and gamma rays. Each kind of light reveals something different about the cosmos. Objects that are invisible to the eye may be glaringly bright in radio waves, or vice versa; infrared light can pierce right through dust clouds that obscure visible light.
"If an object's motion is changing, its gravitational field changes, too."
But gravitational waves are something else entirely: they are gravity's messengers, ripples in the fabric of space that reverberate out from the source of a gravitational disturbance. You can't see them, but you can feel them, like you feel the wake of a passing speedboat on the water. The bigger the boat, the bigger the waves, and so it goes with gravitational waves. Really hefty objects—supermassive black holes containing as much matter as hundreds of millions of suns—make big billows in space-time. Littler things—a moon, a mouse—leave barely a quiver.
Big or small, if an object is just sitting still, its gravitational field is static and unchanging. But if the object's motion is changing, or if its mass is being dramatically rearranged, like in an explosion or implosion, the gravitational field changes, too, and that change produces gravitational waves. A black hole sitting peacefully in isolation is silent and invisible to gravitational wave detectors, but a black hole on a collision-course spiral around another black hole should be positively shrieking. Which is exactly what the LIGO team heard.
(http://www.pbs.org/wgbh/nova/next/wp-content/uploads/2016/02/ligo-beam-tube.jpeg)
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Tubes connect the LIGO optics so the laser beam can pass between them.
LIGO started listening for gravitational waves back in 2002, but, after eight years, it was shut down without recording even one unambiguous gravitational wave detection. But that was okay: Initial LIGO, as the first phase of operations was called, was, in a sense, just for practice. Last September, the real games began. Freshly upgraded with technology that didn't even exist when the LIGO first came online, LIGO, now rebranded Advanced LIGO, is able to detect gravitational waves coming from sources some ten times farther from Earth than before.
LIGO is called an observatory, but it isn't like any astronomical observatory you might be imagining. Each site—there are two currently—is actually a big, L-shaped tube called an interferometer. Each arm is a little more than a meter wide and extends for two and a half miles. Where the two arms meet, a 180 Watt laser beam is split in two; the twin beams travel down the arms, where they hit ultra-precise mirrors and bounce back and forth some 400 times before before meeting again at a light sensor.
Because light is a wave, the two laser beams combine to make an interference pattern of bright and dark areas, or "fringes," at that light sensor. Analyze the fringes, and you can tell how far each light wave traveled to cover the distance between the mirror and the sensor. More importantly, you can tell if that distance is changing over time. If a gravitational wave passes by, one arm of the observatory's "L" should be stretched while the other gets squeezed, producing a telltale change in the fringe pattern.
What Kind of Noise Annoys an Interferometer?
But it gets more complicated. Everything from passing trucks to distant ocean waves can shake the mirrors, causing "noise" that muddies the measurements. That's why LIGO isn't just one machine, but a pair of facilities with identical-twin designs, one located in Livingston, Louisiana and the other Hanford, Washington. By putting almost 2,000 miles between the two instruments, physicists can discriminate between local jiggling, which will only be felt by one detector, and authentic cosmic gravitational waves, which should be felt by both.
(http://www.pbs.org/wgbh/nova/next/wp-content/uploads/2016/02/ligo-Aerial5.jpg)
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LIGO's Hanford, Washington, facility
Still, picking out the tiny signal expected from a gravitational wave from mundane background vibrations is like trying to hear the crickets chirping at an AC/DC concert. The trick is to isolate LIGO's mirrors from external shaking as perfectly as possible. To do that, Advanced LIGO has a completely revamped isolation system that exploits seven different layers of technology to effectively "float" the optics. For LIGO's first run, the mirrors were hung from simple pendulums. This time around, the mirrors are heavier, and each one is suspended from welded glass fibers that hang from a quadruple pendulum—that is, a pendulum that hangs from a pendulum that hangs from a pendulum that hangs from a pendulum. This quadruple pendulum system is great at cushioning the mirrors from very high frequency vibrations.
"Though LIGO's suspension system is much more complex than a car's, it operates on a similar principle," says MIT research scientist Fabrice Matichard, who leads design and testing of Advanced LIGO's seismic isolation system. "When you go very fast, the wheels follow the bumps, but the wheels are decoupled from the frame," so you feel a smooth ride. With LIGO, it's like that, but times four.
To handle lower-frequency tremors, Advanced LIGO is using a new, "active" isolation system that senses and corrects for vibrations in real-time. Outside the LIGO vacuum chamber, a hydraulic system neutralizes the slow swaying coming from distant effects like tides. Inside the vacuum chamber, another set of seismometers triggers two stages of magnetic actuators that counteract mid-frequency vibrations. This active isolation system also keeps in check the Achilles' heel of the pendulum system: its inconvenient tendency to resonate at certain frequencies, making the internal vibrations stronger instead of weaker.
(http://www.pbs.org/wgbh/nova/next/wp-content/uploads/2016/02/sus_llo_fibers.jpeg)
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A member of the pendulum suspension system
Even with all this noise-canceling technology, today, much of the day-to-day business of operating LIGO is trying to understand all the background noise that it picks up. And now, after eight years spent acclimating to the standard noise of the first LIGO run, physicists find themselves back at the beginning.
"The instrument is so different" after the upgrade, says LIGO spokesperson Gabriela González, a professor at Louisiana State University, that the "noise looks very different—in a good way." In fact, the very same active seismic isolation system designed to keep the noise out can introduce new noise as it pushes against the mirrors, noise that in the past would have been imperceptible. Like hunters skilled at finding their prey against one landscape, LIGO scientists must now relearn how to pick out their quarry in a totally new environment.
The Thrill of the Chase
Which is where physicists like Rob Owen come in. "You have to know what you're looking for before you can check whether it's in the data," says Owen, an assistant professor at Oberlin College who is also part of the Simulating Extreme Spacetimes (SXS) collaboration.
Owen and his colleagues use computer simulations to solve the equations of Einstein's general relativity and predict what different sources of gravitational waves will look like to LIGO and other gravitational wave detectors. Computer codes like theirs and those being developed in other labs show how gravitational waves should ring out from a panoply of exotic cosmic collisions: black holes merging with black holes, neutron stars and white dwarfs corkscrewing into each other, and every combination thereof. Their work will help LIGO scientists find what they're looking for in a forest of data.
(http://www.pbs.org/wgbh/nova/next/wp-content/uploads/2016/02/RS232_ModeCleaners-Group003.jpeg)
RS232_ModeCleaners-Group003
These output mode cleaners help improve the quality of laser light.
Before today's announcement the smart money was on neutron stars as the source of the first signals. Neutron stars are the "bread and butter" of LIGO, González says. Less camera-shy than black holes, neutron stars—ultra-dense, fiercely magnetized stellar corpses left behind by supernova explosions—have already been observed by radio telescopes in death-spiral orbits that will ultimately lead them to crash and coalesce, perhaps birthing a black hole in the process. In fact, some of the strongest indirect evidence for gravitational waves had come from observations of a pair of neutron stars known as the Hulse-Taylor pulsar, named for its discoverers, who also won a Nobel prize for their work.
"We know next to nothing about these black holes."
Astrophysicists guesstimate that a single neutron star pair merger happens in our galaxy every 10,000 years or so. "That's too long to wait," González says, but by expanding LIGO's reach to include hundreds of thousands or even millions of galaxies, we can tip the odds in our favor. Right now, LIGO should be able to pick up the signal of a garden-variety neutron star merger if it happens within about 200 million light years of Earth. (The Milky Way, for comparison, is about 100,000 light years across.) As LIGO scientists better understand the sources of noise in the LIGO system, they expect to be able to extend LIGO's reach to some 650 million light years. At that point, González estimates, LIGO should be picking up tens of events each year.
Fortunately, the expanded search technique also applies to the short wavelength gravitational waves from binary black holes, which LIGO is most attuned to detecting. The observatory is most sensitive to small black holes, but there was a chance—which was proven correct—that it could sense in the range of tens or hundreds of solar-masses. Those have proved almost totally resistant to observation with other kinds of observatories. "We know next to nothing about these black holes," González says.
The End of the Beginning
Ultimately, LIGO won't be searching alone. Already, the LIGO group is working in partnership with the European GEO and VIRGO gravitational wave detectors, with plans for collaborations with new instruments, like LIGO-India and the Japanese KAGRA project, in development.
Furthermore, just as traditional telescopes are only sensitive to a certain range of light wavelengths—ultraviolet, say, or radio—LIGO and similarly sized detectors are only built to pick up high-frequency gravitational waves. That means that while LIGO can detect gravitational waves from merging stellar-mass black holes and possibly neutron stars, they are probably deaf to a thick slice of the gravitational wave spectrum, including the low-frequency waves physicists think should be thrumming out from colliding supermassive black holes.
(http://www.pbs.org/wgbh/nova/next/wp-content/uploads/2016/02/7534_20130622155853_DSCF3565_llo_itmx_cp.jpeg)
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LIGO's test mass compensation plates help control for thermal lensing, or the tendency for heat to distort key components.
Two decades from now, an orbiting gravitational wave observatory called eLISA may be able to pick up these low-frequency waves. But in the meantime, far from the big-ticket fanfare, radio astronomers have been developing a clever, bargain-basement technique to try to catch these waves using the "instruments" that nature has provided: millisecond pulsars, rapidly-rotating neutron stars that issue precisely-timed beams of radio waves. By clocking the arrival times of pulsar pulses from across the galaxy, radio astronomers can analyze how space-time is "waving" under the influence of gravitational waves.
The LIGO collaboration also has agreements with 30 different astronomy groups, each poised to swiftly follow up on any future gravitational wave detection with X-ray, ultraviolet, radio, and visible-light telescopes. They are playing a sort of celestial matching game, trying to spot a transitory light source that coincides with the gravitational wave signal. They want to see what LIGO hears.
But it isn't easy. The problem: LIGO gives terrible directions. Together, the twin LIGO detectors can only localize a gravitational wave source to a patch of sky that's many hundreds of square degrees. In a field that large, other telescopes are practically guaranteed to find some now-you-see-it-now-you-don't object. Telling the difference between a true match and a coincidence may be impossible. A decade from now, González and her colleagues hope, LIGO will be just one part of a network of detectors that can provide the kind of localization electromagnetic astronomers need to make confident matches.
For now, though, LIGO—one of the most audacious astrophysical experiments—has proven that gravitational waves exist and that we can detect them. "We couldn't make a baby step," Larson says. "We had to do the big experiment to get the data at all." Which is exactly what they did.
http://www.pbs.org/wgbh/nova/next/physics/advanced-ligo/
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also see ref: Einstein's most incredible prediction may be proven right on February 11
http://www.thelivingmoon.com/forum/index.php?topic=9090.msg121864#msg121864
Gravitational Waves vs. Gravity Waves: Know the Difference! -
http://www.thelivingmoon.com/forum/index.php?topic=9101.msg121968;topicseen#new
I found this very interesting as to What Black Holes maybe and How they that may have effected the Galaxies and Solar System , Planets and Life on Earth..
As well as relatively new ways that they are being observed...and how many seem to be absorbing and sucking in surrounding matter , gases and particles etc in such a way that some become intensely heated that they are actually some of the brightest objects seen in the Universe...and seem to actually be Quasers..
But at the same time they are creating severe energy into the Universe that is created from all that intake and creation of heat.
The Astronomers can now look at how Stars act around certain areas in the Universe.. where there are Black Holes as they orbit around or gradually move into or towards Blackholes.. similar to Planets orbit around Stars..
QuoteHorizon: Swallowed by a Black Hole
2012-2013, Episode 15
In summer 2013, the black hole at the centre of the Milky Way was getting ready to feast. A gas cloud three times the size of our planet strayed within the gravitational reach of our nearest supermassive black hole. Across the globe, telescopes were being trained on the heart of our galaxy, some 27,000 light years from Earth, in the expectation of observing this unique cosmic spectacle. For cosmic detectives across the Earth, it was a unique opportunity. For the first time in the history of science, they hoped to observe in action the awesome spectacle of a feeding supermassive black hole.
http://www.dailymotion.com/video/x22pa65_bbc-horizon-swallowed-by-a-black-hole_news
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This also may relate to it...
What is Reality?
http://www.thelivingmoon.com/forum/index.php?topic=9113.msg122093;topicseen#new