It Wasn’t a Fluke — Scientists See Black Holes Collide Again

Scientists have seen two black holes crash into each other and merge for the second time, proving Albert Einstein was right and showing the first observation was no fluke.

Ultra-sensitive instruments called the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected the ripple in gravitational waves that came across space and time to Earth last December, the team reported Wednesday.

T. Pyle/LIGO / MIT

Last February's announcement that LIGO had detected gravitational waves shook the science world and provided hard evidence to back up Einstein's prediction about gravitational waves in his General Theory of Relativity.

"We can now demonstrate with complete confidence that it wasn't a fluke because we saw something again," said Richard O'Shaughnessy, a team member from the Rochester Institute of Technology.

As before, computers measuring the tiny jiggle made by the waves emitted a chirp.

"This is what we call gravity's music," Gabriela Gonzalez, a Louisiana State University physicist who worked with the team, told a news conference.

Now, the team say they know where and how to look for the waves and they hope to start seeing them frequently.

The two black holes that were reported about in February were super-massive. The two the team spoke about Wednesday were much smaller — one was about 14 times the size of our sun and the other was just eight times as massive. They merged to form a spinning black hole 21 times the mass of our sun.

It gets the not-so-glamorous designation GW151226. It was seen on Dec. 26 of last year, and the team's detailing their reports in Physical Review Letters. The team's been sitting on the findings while they verified all the measurements. In the meantime, they reported on the first collision, seen in September of last year.

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"By December we were sure that the first event was genuine and we had a fairly mature draft of that paper, which finally came out in February," said Peter Shawhan, a University of Maryland physicist who also worked on the team. "But it was very satisfying to know, even then, that we already had a second event on our hands."

Artist's rendition of the two colliding binary black hole systems detected by LIGO. Image credit: LIGO/A. Simonnet. / CALTECH

"It's fabulous that our waveform models have pulled out from the noise such a weak but incredibly valuable gravitational wave signal," said Alessandra Buonanno, a physics professor at the University of Maryland who was part of the team.

"GW151226 perfectly matches our theoretical predictions for how two black holes move around each other for several tens of orbits and ultimately merge," Buonanno added. "Remarkably, we could also infer that at least one of the two black holes in the binary was spinning."

The collision happened 1.4 billion years ago. It's taken that long for the gravitational waves to reach Earth.

Black holes are powerful objects, collapsed stars that pull in vast quantities of matter and concentrate them into a very small area.

When two black holes come close to one another, they're pulled together, shaking the fabric of space-time. These waves then spread, a little bit like ripples expanding from the plunk of a pebble in water. Or at least, that's what Einstein predicted. Two observations in a row substantiate the theory.

Because these black holes were smaller, the wobble was fainter, but it lasted for longer than the first reported event, the team reported. "This signal isn't obvious," said John Whelan of the Rochester Institute of Technology. "We had to use a more sophisticated technique to find it called matched filtering." It took months of work to model what the scenario would have been like.