Three supermassive black holes have been spotted merging into one

Three galaxies with supermassive black holes at their centers appear to be in the process of collapsing. merger into a single giant galaxy, a process that astronomers have rarely seen.

Astronomers believe that in order to grow to such enormous sizes, supermassive black holes must occasionally devour or merge with other massive black holes during galactic collisions. This process is difficult to detect, both because these mergers are short-lived compared to the life of a black hole, and because black holes can only be easily seen if they emit light by actively feeding on material, which is also rare. As a result, astronomers have only caught about 150 pairs of galactic black holes in the process of merging.

Now, Emma Schwartzman from the US Naval Research Laboratory in Washington and her colleagues have discovered a group of three supermassive black holes, all of which are actively feeding and appear to be coalescing into a single system. “The more galaxies involved, the sparser the system becomes,” says Schwartzman.

Each supermassive black hole emits low-frequency radiation in the form of radio waves, which can pass through dust that blocks other light. This allowed Schwartzman and her team to observe them using two radio observatories, the Very Long Baseline in Hawaii and the Very Large Array in New Mexico, and then rule out that the light came from another source, such as bright galaxies full of stars.

“What's really interesting is that all three of these [black holes] emit in radio mode, which we have never seen before,” says Schwartzman. “There is no guarantee that any [black hole] will emit in radio mode.”

According to scientists, there are already visible signs that galaxies have begun to interact with each other. Isabella Lamperti at the University of Florence, Italy, but they are at a relatively early stage of interaction, given that the two galaxies are still separated by about 70,000 light-years and the third is 300,000 light-years away.

But given their combined lifespans of billions of years, we are witnessing the end of history. “It's like the final moments of a galaxy merger soap opera,” says Only Emma at the Ruhr University Bochum, Germany.

She said simulating the merger of three active supermassive black holes is extremely difficult, but observing the system will allow physicists to better understand what happens in more complex mergers. “This is the first step towards understanding the physics of the system,” says Kuhn.

Secrets of the Universe: Cheshire, England

Spend a weekend with some of science's brightest minds as you explore the mysteries of the universe on an exciting program that includes a tour to see the famous Lovell Telescope.