Astronomers Discover the Biggest Black Hole Merger Ever

Researchers working at LIGO and the Virgo Collaboration say they’ve detected the most massive black hole merger ever recorded. The extraordinary black hole merger, dubbed GW190521, formed from a pair of black holes that were 66 and 85 times the mass of the Sun. The resultant remnant black hole stands as the first “intermediate-mass” black hole ever discovered.

The researchers detected the black-hole merger on May 21, 2019. They made the detection using LIGO—or the Laser Interferometer Gravitational-Wave Observatory—in the U.S. and the Virgo detector in Italy. The observatories were able to pick up on the gravitational waves—or ripples in the fabric of spacetime—produced by the merger.

“This is the first time that LIGO has detected evidence of [an intermediate-mass black holes] existing,” Dr. Chris Messenger says in the video above. Messenger, a professor at the University of Glasgow who’s involved with LIGO, says this isn’t only the first time the observatory has detected an intermediate-mass black hole, but the first time anyone has.

In a report from The Verge, Salvatore Vitale, an assistant professor at MIT’s LIGO Lab, says this kind of intermediate-mass black hole is “the missing link between [black holes with] tens of solar masses and millions.” Vitale also told The Verge scientists have been baffled as to why the black holes hadn’t been found before.

In the video below, Mark Myers at the ARC Centre of Excellence for Gravitational Wave Discovery ( OzGrav) provides an animation of the merger. Myers notes in the video that the remnant black hole left over from the merger has a mass 142 times that of the Sun. But while that mass puts GW190521 in the intermediate-mass black hole range, its parent black holes were in a “forbidden range” themselves. (Energy emission from the collision accounts for the lost mass.)

As Myers notes, the larger of the two original black holes was 85 solar masses—or 85 times the Sun’s mass. This puts it in the so-called forbidden range for black-hole masses, which spans from 65 to 135 solar masses. Myers says this is the case because the requisite stars for these black holes should annihilate rather than collapse. And yet, the star responsible for the 85-solar-mass black hole did not. (It’s unclear why the other black hole, at 66 solar masses, doesn’t fall into the forbidden range.)

On top of being massive, GW190521 is also the most distant gravitational-wave source ever detected. The merger may have happened at a distance of up to 7.7 billion light-years away. Which means this event happened up to 7.7 billion years ago.

Moving forward, the researchers studying GW190521 want to figure out the mystery behind the larger constituent black hole. One possibility is that the 85-solar-mass black hole was itself formed from two other black holes. Or perhaps it stole mass from a star. Regardless, with the remnant black hole, it seems these researchers have found a key missing piece of the cosmic puzzle.

Feature image: Mark Myers, ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)

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