Astronomers explore the origins of black holes after 39 new cosmic collisions have been detected

The number of gravitational wave events caused by massive collisions between black holes and neutron stars has quadrupled. In a series of new papers, researchers from the LIGO and Virgo collaborations have cataloged 39 “new” events, adding to 11 already detected since the LIGO and Virgo gravitational wave detectors were activated in 2015.

Gravitational waves are ripples in space-time caused by collisions between black holes and other extreme cosmic phenomena. When massive cosmic bodies merge, they release exceptional amounts of energy, causing a wave to propagate from their location. Eventually, that wave laps the Earth, sending beeps to detectors in the United States (LIGO) and Italy (Virgo). Gravitational wave detections have revolutionized the way we see the universe, helping scientists understand some of the most mystifying objects in space.

The new catalog, announced Wednesday, is known as GWTC-2 and features 50 total events, including black hole mergers, neutron star mergers, and potentially collisions between a black hole and a neutron star. Thirty-nine events were detected between April 1 and September 30, 2019 the LIGO and Virgo facilities have received a number of updates, increasing their sensitivity.

The catalog update includes some of the most extreme cosmic collisions ever detected, including one revealed in September which created a black hole 150 times more massive than the sun – the largest ever seen – e a particularly unusual fusion between a black hole and a “mysterious object” this does not seem to fit with previous findings.

But the motherlode fusion has excited gravitational wave astronomers because it gives them a ton of new data with which to probe the very nature of these extreme cosmic collisions.

“It’s kind of like the difference between finding a single Iguanodon bone and finding hundreds of Iguanodon fossils,” says Eric Thrane, an astrophysicist at Monash University in Melbourne, Australia, and lead investigator with OzGrav, an Australian research center that studies gravitational waves.

In a new prepress paper, presented to Astrophysical Journal Letters, the collaboration studied 47 of the 50 events and analyzed the physical properties of black hole mergers.

“Black holes are fascinating objects because they are very simple,” says Thrane. “They only have two numbers that describe them: their mass and their spin.”

The spin of a black hole can be determined by the gravitational wave signal. This offers scientists a window into how black holes meet and fall into each other in deep space, revealing how they met.

Black holes are created when huge stars collapse on themselves. Sometimes, two stars have been orbiting each other for eons in what is known as “binary”. Over time, they lose their mass and eventually die, collapsing to form black holes. But they continue to orbit each other until they collide and form a much larger black hole. In this case, the rotation does not change – it points in the same direction.

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On the other hand, if black holes roamed the cosmos in dense clusters of stars, all alone, then collided with each other, the theory suggests that this could mess up their rotation. “When that happens, you’d expect the rotation to be pointed in different directions,” says Thrane.

Importantly, with the truckload of new observations, the LIGO and Virgo collaboration is seeing both types of black holes.

“We are getting to the origin of where black holes come from and where [and] how they come together and blend, ”says Thrane.

The latest observation conducted by LIGO and Virgo, O3b, took place between November 1, 2019 and March 27, 2020 before being stopped due to the coronavirus pandemic. Data from this period are currently being analyzed and will expand the catalog of gravitational wave events, once again improving our understanding of extreme cosmic collisions.