Thursday, June 01, 2017


Researchers at LIGO, the Laser Interferometry Gravitational-Wave Observatory, announced today their third detection of space-time vibrations from the collision of of a pair of black holes, in this case nearly three billion light-years from Earth.

In terms of mass, this new black hole merger--which created a black hole with a mass 49 times heavier than our Sun--fell neatly between the two earlier detections, in September and December of 2015. Those two cosmic crashes resulted in black holes with 62 and 21 times the Sun's mass respectively, and took place much closer to Earth.

The current crash was between black holes with estimated masses of 31.2 and 19.4  times that of the Sun. That means that a mass equal to two Suns was converted into gravitational waves in a fraction of a second as the two black holes completed their death spiral.

Simulated black-hole merger
Credit: LIGO Lab Caltech

This third detection tells the scientists that the unique new window on the cosmos provided by gravitational-wave detectors is now wide open. With improved sensitivity of LIGO's existing laser interferometers and the addition later this year of a third detector, called Virgo, the researchers hope to be able to detect black hole mergers and other space-time-shaking events on a daily basis.

Aerial view of the Virgo interferometer near Pisa, Italy
Credit: The Virgo Consortium

Besides further proof of the existence of black holes in this mass range, the detection allowed researchers to test one of the predictions of Einstein's General Relativity--that gravitational waves travel through space at the same speed regardless of their frequency. Once again, General Relativity passed the test.

“It is remarkable that humans can put together a story, and test it, for such strange and extreme events that took place billions of years ago and billions of light-years distant from us," says MIT's David Shoemaker, LIGO's spokesperson.

The number of black holes in this mass range raises the intriguing possibility that they may at least partly explain dark matter, which is known to exist because of its gravitational effects on galaxies and galaxy clusters, but whose nature remains mysterious.

"There's this intriguing indication that with the size of black holes, 10-100 solar masses, in about the quantity that we see them or expect to see them, might account for dark matter," says LIGO researcher Mike Landry. "It's not impossible."

For the first time, researchers were able to suss out information about how the black holes were spinning before they collided. It's more likely than not that the black holes were not spinning in the same plane as their orbit. That, in turn, implies that they may have formed far apart and only later fell into each other's gravitational thrall.

As gravitational-wave astronomers detect more of these incredibly powerful cosmic events, and gain the ability to match them with observations using visible light, infrared, X-rays and gamma rays, astrophysicists, nuclear physicists and cosmologists all expect exciting new findings that will cast light on black holes, neutron stars, dark matter and the nature of space-time itself.

The new findings appear in this week's edition of Physical Review Letters.

You can view some great video simulations at LIGO's YouTube channel.

You can become a citizen scientist helping to sift actual gravitational-wave signals from the noise by participating in GravitySpy or Einstein@Home.

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