Scientists confirm fourth detection of gravitational waves

Finding is first for new Virgo detector that began operating on August 1.
By Laurel Kornfeld | Sep 27, 2017
Gravitational waves, ripples in spacetime produced by colliding black holes, were detected for the fourth time since their initial discovery in 2016.

The detection is a first for a new gravitational wave detector named Virgo, which identified the waves on August 14, less than two weeks after it became operational in Italy on August 1.

LIGO, the Laser Interferometric Gravitational Wave Observatory, with instruments in Washington State and Louisiana, also detected the August 14 gravitational waves.

Virgo was added as a new detector because the initial two LIGO instruments could not determine with the origin of waves detected with sufficient certainty.

According to Imre Batos of the University of Florida, having just two detectors meant a wave could come from anywhere in a banana-shaped region that makes up one-fortieth of the night sky area.

Adding Virgo reduced uncertainty over the source of waves detected by LIGO by ten times, noted LIGO and Virgo scientists.

Constructed of tubes several kilometers long with L shapes that split laser light and send it down each tube end, then rejoin it in a detector, gravitational wave detectors measure tiny movements of laser beams that move in and out of phase with one another, producing a waveform scientists can subsequently analyze.

Through analysis of the waveforms, researchers gain insight into their properties and origins.

With Virgo's assistance in locating the source of waves detected, scientists can immediately aim telescopes toward the area of the sky from which the waves come.

"The main advantage of knowing the direction is that you can take a telescope in that direction and see if anything else is coming from the source," Batos explained.

Events that produce gravitational waves, such as the collisions of two neutron stars or black holes, can sometimes also be observed in visible light.

The gravitational waves detected by both Virgo and LIGO on August 14 were produced by the collision of two black holes approximately 1.8 billion light years from Earth, one with 31 solar masses, and the other with 25 solar masses. The two merged into a larger single black hole with 53 times the mass of our Sun.

In this process, three solar masses were transformed into energy that powered the gravitational waves.

Scientists from both LIGO and Virgo announced the discovery at a G7 meeting of science ministers in Turin, Italy. It is also detailed in a paper published in the journal Physical Review Letters.

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