Just what are gravitational waves?

In an artist's conception, a binary black hole produces gravitational waves that travel outward and carry energy away from the system. Such waves have finally been detected, scientists announced Thursday.


WASHINGTON (AP) — In an announcement that electrified the world of astronomy, scientists said Thursday that they have finally detected gravitational waves, the ripples in the fabric of space-time that Albert Einstein predicted a century ago in his General Theory of Relativity.

Astronomers hailed the finding as an achievement of historic proportions, one that opens the door to a new way of observing the universe and the violent collisions that are constantly shaping it. For them, it's like turning a silent movie into a talkie because these waves are the soundtrack of the cosmos in action.

"Until this moment, we had our eyes on the sky and we couldn't hear the music," said Columbia University astrophysicist Szabolcs Marka, a member of the discovery team. "The skies will never be the same."

An international team of astrophysicists used a $1.1 billion set of twin instruments known as the Laser Interferometer Gravitational-wave Observatory, or LIGO, to detect a gravitational wave generated by the collision of two black holes 1.3 billion light-years from Earth.

"Einstein would be beaming," National Science Foundation director France Cordova said.

WHAT IS A GRAVITATIONAL WAVE?

Gravitational waves are extremely faint ripples in the fabric of space and time that come from some of the most violent events in the universe. In this case, it is from the merger of two black holes 1.3 billion light-years away. The way to think of this is to imagine a mesh net and visualize pulling on its ends. The resulting kinks are sort of like what a gravitational wave does.

WHAT IS SPACE-TIME?

Space-time is the mind bending, four-dimensional way astronomers see the universe. It melds the one-way march of time with the more familiar three dimensions of space. General relativity says gravity is caused by heavy objects bending space-time. And when massive but compact objects like black holes or neutron stars collide, their immense gravity causes space-time to stretch or compress.

HOW IS THIS 'HEARING' THE COSMOS?

Scientists mostly use the word "hear" when describing gravitational waves, and the data does, in fact, arrive in audio form. The researchers can don headphones and listen to the detectors' output if they want. On Thursday, to prove they found a gravitational wave, the researchers played a recording of what they called a chirp.

HOW CAN THEY BE CERTAIN THIS IS REAL?

Astronomers sat on the discovery for nearly five months, since Sept. 14, checking back and forth to make sure it was right. They considered all sorts of Earth-bound interference or noise, examined the possibilities and eventually dismissed them.

The astronomers are so cautious that they routinely have other scientists deliberately inject false data to test their abilities. In those tests, the observatory team was able to show that the injected data wasn't real. In the case of the discovery announced Thursday, they are extra certain they are not seeing injected or hacked data because the system that allows false information to be inserted was down at the time.

In addition, the team of 1,004 scientists on the project looked over the data, and the results were then peerre viewed by even more experts and published in the journal Physical Review Letters.

WHAT'S NEXT?

Expect more waves. It could be as many as a few a month or as little as a few per year. The observatory is also being further upgraded to hear even fainter, more distant waves.

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