It’s not often that physicists get a standing ovation.
But they got one Thursday morning as a team announced they’d detected the collision of two black holes 1.3 billion years ago, the echo riding on gravitational waves across the universe just as Albert Einstein predicted.
“Ladies and gentlemen, we have detected gravitational waves,” David Reitze, executive director of Caltech’s twin Laser Interferometer Gravitational-Wave Observatory (LIGO) laboratory, said at a news conference in Washington, D.C.
“We did it!” Reitze said to applause.
“These gravitational waves were produced by two colliding black holes that merged to form a single black hole 1.3 billion years ago.”
Such a collision has never been seen before. Black holes are powerful objects, collapsed stars that pull in vast quantities of matter and concentrate them into a very small area.
These two were about 150 km, just under 100 miles, in diameter. “Pack 30 times the mass of the sun into that,” Reitze said. “Accelerate it to about half the speed of light.”
Two of these massive, fast-moving objects circled one another, crashed, and merged to form a single black hole.
“That’s what we saw here. It’s mind-boggling,” Reitze said.
It was a monstrous collision, so big that it literally shook the fabric of space-time.
These waves then spread a little bit like ripples expanding from the plunk of a pebble in water.
“It goes right through matter, right though stars,” Reitze said. After 1.3 billion years, across trillions of miles of space, the waves are infinitesimally small — 1/1000th the size of a proton, a subatomic particle.
But these small waves still stretch and compress space. It took special detectors — the LIGO system — to detect these tiny, tiny ripples.
“You can see that the Earth is jiggling like jello,” Reitze said.
"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," Rainer Weiss, an emeritus professor of physics at MIT who was part of the team that originally proposed building LIGO, said in a statement.
"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,” added Kip Thorne, Caltech's Richard P. Feynman Professor of Theoretical Physics.
It’s really hard to detect these tiny movements, so researchers built LIGO, a pair of 2.5 mile long, L-shaped interferometers that use laser light split into two beams that travel back and forth down its arms. They monitor the distance between mirrors precisely positioned at the ends of the arms. Gravitational waves would move the mirrors just slightly.
Having one in Louisiana and one in Hanford, Washington, helps satisfy scientists that what is making the mirrors wiggle is coming from off the planet.
They went online last September after some adjustments. No one thought they’d get a signal so fast.
Northwestern University physicist Vicky Kalogera was at home when it happened.
“That evening, while preparing dinner for my family, I saw a text message from a graduate student in my LIGO group: ‘Have you been keeping up with LIGO emails today? Loud trigger!’ “ Kalogera said.
“I dropped everything, went to my laptop and started reading the emails. And there was a clear sense that we have a signal in our data. A gravitational wave signal that is very loud, very strong, and we definitely have to do something about it and figure out what exactly it is.”
Each LIGO facility had recorded the same signal at almost the same time.
“It was exactly what you would expect when Einstein’s theory of relativity would predict with two massive objects like black holes circling and merging together,” Reitze said.
“To detect something in the first few days after turning on our new detectors and to have a detection of an unexpected source – ‘heavy’ binary black holes -- is just amazing,” Kalogera said
“What is really exciting is what comes next,” Reitze said. “I think we are opening a window on the universe.”
Physicists use visible and other spectra of light, x-rays and microwaves to observe the universe. Now they can use gravitational waves, too.
“Up to now, we have been deaf to gravitational waves. Now we can hear them,” Reitze said.
“We are going to be able to hear more of these things. …We may see things that we never saw before.”