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Two Merged Black Holes Detected

Researchers have detected the violent merger of two black holes rippling the fabric of space and time like a bed sheet in the breeze, demonstrating how astrophysicists are using newly discovered gravitational waves to reveal forces shaping the cosmos.

Announcing their find on Thursday, the scientists said they recorded these primordial shock waves, which originated three billion light-years away from Earth, by using the twin detectors of the $1.1 billion Laser Interferometer Gravitational-Wave Observatory. Last year, the LIGO team detected evidence of gravitational waves for the first time and helped confirm Einstein’s theory of general relativity.

The discovery, reported in the journal Physical Review Letters, offers new clues to how black holes can grow to many times the mass of the sun, like those that lurk at the heart of virtually every galaxy, and hints at the role they may play in the evolution of the universe. More than a thousand scientists were involved in the effort, led by the California Institute of Technology and the Massachusetts Institute of Technology.

Artist's conception shows two merging black holes similar to those detected by Laser Interferometer Gravitational-Wave Observatory.PHOTO: LIGO/CALTECH/MIT/SONOMA STATE

The announcement marks the third time in just over a year that the LIGO researchers have successfully detected an object by measuring the physical warping of space caused by gravitational waves. All three discoveries involved black holes—massive objects that cannot be seen directly by ordinary means because their gravity is so intense that no matter, light or other radiation appears to escape.


“Before our discoveries, we didn’t even know for sure that black holes truly existed,” said LIGO astrophysicist Laura Cadonati at the Georgia Institute of Technology.

In their newest work, researchers at sprawling LIGO installations located in Livingston, La., and Hanford, Wash., registered the gravitational tremors from the crush of two ancient black holes, each one spinning on its axis like a tornado as they spiraled together and then joined in a violent embrace. In an explosive third of a second, they released the combined energy of two stars—more energy in that instant than from all the light from all the galaxies in the universe, the scientists said.

A mathematical simulation of the warped space-time near two merging black holes, consistent with LIGO's observation of the event dubbed GW170104. The colored bands are gravitational-wave peaks and troughs, with the colors getting brighter as the wave amplitude increases. PHOTO: LIGO/CALTECH/MIT/SXS COLLABORATION

To pick up the perturbations, the detectors monitored how long it takes a controlled laser beam to travel between suspended mirrors. Ripples in space-time can alter the distance measured by the light beam, causing the amount of light falling on the LIGO photo-detectors to vary minutely. Only the most violent events in the cosmos produce waves strong enough to register.

“Normally, we don’t think of the nothing of space as having properties,” said Caltech physicist Michael Landry, head of the Hanford LIGO facility. “We register the passage of those gravitational waves as they change the length of our two detectors.”

The scientists calculated that one black hole was 19 times the mass of the sun and its companion was 31 times the mass of the sun. They merged into a single black hole about 49 times the mass of the sun, said LIGO physicist Bangalore Sathyaprakash at Pennsylvania State University and the U.K.’s Cardiff University.

In the years ahead, the researchers expect gravitational waves to unveil a universe to which conventional telescopes, scanning the sky for visible light and other electromagnetic wavelengths, are blind.

“We are really moving to a new astronomy of gravitational waves,” said MIT physicist David Shoemaker, the LIGO project’s elected spokesman.