Are two colliding black holes not enough? Do it three

In 2016, scientists first detected the collision of two distant black holes, using the Laser Interferometer’s Gravitational Wave Observatory, or LIGO, a pair of L-shaped antennas in Hanford, Washington, and Livingston, Louisiana. Since then, LIGO and a third antenna, Virgo, located in Italy, together have charted dozens of similar catastrophic marriages in the dark. But astronomers have yet to see any light trails of them. (An exception was a collision of neutron stars, the remnants of supernova explosions, which lit up the universe and were detected in August 2017)

On May 21, 2019, an alert was sent to world astronomers that the LIGO and Virgo antennas had recorded what looked like two colliding black holes. Among the telescopes on duty that night was the Zwicky Transient Facility, a robotic instrument on California’s Palomar Mountain that monitors the deep sky for anything that turns on, flickers, explodes, or moves. It is named after Fritz Zwicky, an innovative and eccentric Swiss astronomer who worked at Caltech.

Dr. Graham, the project scientist for the Zwicky Telescope, and his colleagues had been reflecting on the possibility of black hole mergers occurring in the dense, shiny supermassive black hole accretion disks, which are the central engines of quasars. The team began monitoring quasars in those regions for unusual activities.

The trace of the May gravitational wave event led to a quasar known as J124942.3 + 344929, located about 4 billion light-years from Earth. Examining the records of the Zwicky telescope, Dr. Graham discovered that the quasar had exploded, doubling in brightness for about a month, an unusually large fluctuation. That marked it as a possible black hole collision, he said.

Reinforcing that hypothesis was the fact that the flare did not become visible until 34 days after the gravitational waves were detected. According to a model that Dr. Ford and Barry McKernan, his colleague from the American Museum of Natural History, described in an article, it would take so long for any light to come out of a black hole collision. last year.

Dr. Ford described the accretion disk as “a swarm of stars and dead stars, including black holes,” in a Caltech press release.

She added: “These objects swarm like angry bees around the monstrous queen bee in the center. They can briefly find gravitational partners and pair up, but they generally lose their partners quickly in the crazy dance. But in the disk of a supermassive black hole, the flowing gas turns the swarm well into a classic minuet, arranging the black holes so they can pair up. “