Two colliding galaxies may have birthed this black hole

Something unusual may have risen from the ashes of an epic smashup.

In the middle of a galaxy shaped like an infinity symbol — thought to be the result of two galaxies colliding — sits a supermassive black hole. The enormous celestial body may have emerged from the crash’s gaseous wreckage, researchers report in the July 20 Astrophysical Journal Letters. This observation could provide the best evidence yet that these mysterious, massive objects can form from collapsing gas clouds.

“We don’t know a lot about what type of circumstances can lead to” black holes potentially forming this way, says astronomer Ragadeepika Pucha of the University of Utah in Salt Lake City, who was not involved in the work. If the identified black hole’s proposed origin is proven, “it’s the first step towards understanding a lot of physics that’s happening with the direct-collapse scenario.”

Two years ago, astronomer Pieter van Dokkum of Yale University and colleagues were sifting through data from the James Webb Space Telescope, or JWST, when an odd galaxy caught their eye. The newfound object resembles two slightly overlapping rings with dots at the center of each, inspiring the name Infinity galaxy. Its light took about 8 billion years to reach Earth.

The galaxy’s unusual shape and previous computer simulations suggested it was once two separate galaxies. Observations from other telescopes revealed signs of an actively growing black hole. The galactic weirdo emits X-rays and radio waves, as well as light indicating the presence of atoms stripped of some electrons through a highly energetic process. Those clues suggest a disk of hot material rotating around and feeding a black hole. More JWST data confirmed the celestial body’s existence along with a surrounding gas cloud.  

But “what was surprising was the location” of the black hole, van Dokkum says. “We expected that all the emission would be coming from one of the two nuclei” — the dots within the rings. Those were the centers of the previous two galaxies, where supermassive black holes often reside. “It turned out [the emission] came from the middle, from the region in between those two nuclei.”

The team suspects that the enormous black hole, with an estimated mass 1 million times that of the sun, was born from a messy galactic meetup. As the galaxies encountered one another, gravitational interactions caused their stars to form two rings, which past evidence suggests can occur, van Dokkum says. But he and his colleagues believe the collision also compressed the galaxies’ gas, creating a big, dense clump that became a black hole — instead of several smaller clumps that typically form stars.

“Gas needs to be very calm to form stars,” van Dokkum says. “Here we think that the motions of the gas and the amount of turbulence in the gas is too high to allow that.” Another possibility is that the gas formed a dense cluster of stars that collapsed and created the black hole, he says.

Researchers aren’t sure how supermassive black holes form. One idea is that they come from smaller black holes merging over time. But JWST and other telescopes have uncovered several huge black holes that existed too soon after the universe began for that proposition to explain them. Another hypothesis suggests that these giants form in one go from singular gas clouds following dramatic events, as proposed for the one spotted in the Infinity galaxy. That scenario is “very controversial” because of the special circumstances required, Pucha says.

The next step, van Dokkum says, is to create computer simulations that assess how galactic gases behave during a crash. That will verify whether it’s even possible to birth a supermassive black hole this way.

No matter what future tests find, the Infinity galaxy has sparked wonder since its discovery. “We knew we were looking at something extraordinary,” van Dokkum says. “We just, in the beginning, had no idea what.”