Gravitational waves have given a new black hole a high-speed ‘kick’

This black hole really knows how to recede.

Recently, scientists noticed two black holes united into one, and in the process they got a “kick” that knocked out the newly formed black hole at high speed. This black hole zoom out At about 5 million kilometers per hour, plus or minus a few million, researchers report in a research paper in the press Physical Review Letters. That’s very fast: the speed of light is only 200 times.

Ripples in spacetime, called gravitational waves, shot the black hole at its fast exit. As any two paired black holes spiral inward and unite, they emit these ripples, which expand and compress space. If these gravitational waves are fired into the universe preferentially in one direction, the black hole will bounce back in response.

It’s like shooting a gun after a bullet, says astrophysicist Vijay Varma of the Max Planck Institute for Gravitational Physics in Potsdam, Germany.

The gravitational wave observatories LIGO and Virgo, located in the United States and Italy, detected the space-time ripples of black holes when they reached Earth on January 29, 2020. These waves revealed details of how black holes merge, hinting at the possibility of a big kick in. . When the black holes orbited each other, the plane they were orbiting rotated, or preceded, similar to how the top wobble as it rotated. Pre-existing black holes are expected to get even bigger kicks as they merge.

So Varma and his colleagues delved into the data, measuring whether a black hole had got the boot. To estimate the kick’s speed, the researchers compared the data with the various expected versions of black hole mergers, which were generated based on computer simulations that solve the equations of general relativity, Einstein’s gravitational theory (SN: 2/3/21). The researchers found that the bounce was so large that the black hole may have been ejected from its home and kicked to the cosmic edge.

Dense groups of stars and black holes called globular clusters are one of the regions where black holes are believed to cooperate and merge. According to the team, the probability of an expelled black hole remaining within a globular home cluster is only 0.5%. For a black hole in another type of dense environment, called a nuclear star cluster, the warp probability was about 8%.

The great escape of a black hole could have major repercussions. LIGO and Virgo discover stellar-mass black hole mergers, which form when a star explodes in a supernova and collapses into a black hole. Scientists want to understand whether black holes that combine into crowded groups can cooperate again, via multiple rounds of merging. If they did, it might help explain some Surprisingly huge black holes previously seen in mergers (SN: 9/2/20). But if merging black holes were to be rocketed far from home, that would reduce the likelihood of multiple mergers.

“The kicks are very important in understanding how heavy stellar-mass black holes form,” Varma says.

Previously, astronomers have found evidence of giving off gravitational waves Big kicks for supermassive black holesthe biggest monsters found in the centers of galaxies (SN: 3/28/17). But that conclusion hinges on observations of light, rather than gravitational waves. “Gravity waves are, in a way, cleaner and easier to explain,” says astrophysicist Manuela Campanelli of the Rochester Institute of Technology in New York, who was not involved in the new study.

LIGO and Virgo data have already revealed some evidence of black holes getting their little kicks. The new study is the first to report using gravitational waves to detect a black hole on the receiving end of a big kick.

That big kick, Campanile says, is no surprise. Previous theoretical predictions by Campanile and colleagues suggested that such powerful kicks are possible. “It’s always exciting if someone can measure what you’ve predicted from calculations through observations.”