Paper. (open access)
LIGO signal reveals first observation of two massive black holes colliding, proves Einstein right.
Now for the first time, scientists in the LIGO Scientific Collaboration — with a prominent role played by researchers at MIT and Caltech — have directly observed the ripples of gravitational waves in an instrument on Earth. In so doing, they have again dramatically confirmed Einstein’s theory of general relativity and opened up a new way in which to view the universe.
But there’s more: The scientists have also decoded the gravitational wave signal and determined its source. According to their calculations, the gravitational wave is the product of a collision between two massive black holes, 1.3 billion light years away — a remarkably extreme event that has not been observed until now. More.
Here’s a bit of background from Quanta:
Gravitational waves are perhaps the most elusive prediction of Einstein’s theory, one that he and his contemporaries debated for decades. According to his theory, space and time form a stretchy fabric that bends under heavy objects, and to feel gravity is to fall along the fabric’s curves. But can the “space-time” fabric ripple like the skin of a drum? Einstein flip-flopped, confused as to what his equations implied. But even steadfast believers assumed that, in any case, gravitational waves would be too weak to observe. They cascade outward from certain cataclysmic events, alternately stretching and squeezing space-time as they go. But by the time the waves reach Earth from these remote sources, they typically stretch and squeeze each mile of space by a minuscule fraction of the width of an atomic nucleus.
Einstein’s equations of general relativity are so complex that it took 40 years for most physicists to agree that gravitational waves exist and are detectable — even in theory.
Einstein first thought that objects cannot shed energy in the form of gravitational radiation, then changed his mind. He showed in a seminal 1918 paper which ones could: Dumbbell-like systems that rotate about two axes at once, such as binary stars and supernovas popping like firecrackers, can make waves in space-time.
Still, Einstein and his colleagues continued to waffle. Some physicists argued that even if the waves exist, the world will oscillate with them and they cannot be felt. It wasn’t until 1957 that Richard Feynman put that question to rest, with a thought experiment demonstrating that, if gravitational waves exist, they are theoretically detectable. But nobody knew how common those dumbbell-like sources might be in our cosmic neighborhood, or how strong or weak the resulting waves would be. “There was that ultimate question of: Will we ever really detect them?” Kennefick said. More.
From New Scientist
There were lingering worries that this signal could have been a deliberate fake. The LIGO team is infamous for secretly introducing ersatz gravitational wave signals into the data stream to test the experiment’s analysis procedures.
A previous “detection” in 2010 was sunk this way, but experienced team members knew something comforting this time around: fake signals aren’t inserted into engineering runs.
Other false positives could come from the accidental insertion of a pattern that looks like a signal, or even from malicious tampering. But by following procedures to check each instrument and each step in the data analysis, the team ruled these out, too.
The big reveal, which team members call “opening the box”, was on a conference call on 5 October. At the agreed-upon moment, a graph showing how likely it was that this signal was due to chance went live. The event was overwhelmingly likely to have been real. More
See also: Black hole size could kill general relativity? (Maybe not just yet 😉 )
Gravitational waves are so exciting because they were the last major prediction of Einstein’s general theory of relativity that had to be confirmed, and discovering them will help us understand how the Universe is shaped by mass.
“Gravitational waves are akin to sound waves that travelled through space at the speed of light,” said gravitational researcher David Blair, from the University of Western Australia. “Up to now humanity has been deaf to the universe. Suddenly we know how to listen. The Universe has spoken and we have understood.”
What does that mean for us? Just think of all the breakthroughs that have come thanks to the discovery of x-rays and radio waves – now that we can detect gravitational waves, we’re going to have a whole new way to see and study the Universe.
From Discovery News:
Like radio waves, visible light, X-rays and other forms of electromagnetic radiation, Einstein believed that gravity also travels in waves. But even the most energetic events in the universe, such as two black holes crashing together, would cause only the slightest rippling through space and across time.
After decades of failed attempts, scientists fished out the first confirmed measurement of gravitational waves passing through Earth, a detection that required measuring 2.5-mile long L-shaped laser beams to a precision 10,000 times smaller than a proton.
Since everything from traffic to earthquakes will distort the beams, the Laser Interferometer Gravitational-Wave Observatory, or LIGO, consists of two detectors separated by 1,865 miles. Because gravitational waves are believed to travel at light speed, a detection from a cosmic source picked up at one LIGO site should be followed up by an identical detection in the other 10 milliseconds later.
That’s exactly what scientists saw when they fished out waves set off by a pair of black holes 1.3 billion light-years from Earth spiraling toward each other and then colliding to form an even larger black hole, researchers said at a webcast press conference Thursday. More.
Well, this didn’t take very long. The flapdoodle begins:
From The Weather Network
Also, with this detection, a whole new branch of astronomy opens up. Gravitational waves carry information along with them – specifically about the events that caused them, but possibly about the spacetime they’ve travelled through since then. This is information that can’t be obtained using any other kind of astronomy, so it gives us a whole new way of looking at the universe around us.
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