This is the first known galaxy to have three supermassive black holes
Supermassive black holes act as the engines powering the centers of galaxies, including our own Milky Way galaxy. But in a first, scientists have observed that one galaxy contains three supermassive black holes at its core and they’re surprisingly close together.
The galaxy, NGC 6240, has an unusual shape, which previously led scientists to believe that it was created when two smaller galaxies collided and began to merge. NGC 6240 is relatively close to us by universal standards at 300 million light-years away, so astronomers have been able to study it in all wavelengths of light.
It was seen as a standard for galactic interaction and scientists thought that due to the merger, there were likely two black holes at its core.
But new observations revealed a third supermassive black hole at the center of the galaxy. Each black hole has the mass of more than 90 million suns each.
The findings were published Thursday in the journal Astronomy & Astrophysics. The new observations of the galaxy were obtained by the European Southern Observatory’s Very Large Telescope in Chile.
“Through our observations with extremely high spatial resolution we were able to show that the interacting galaxy system NGC 6240 hosts not two — as previously assumed — but three supermassive black holes in its centre,” said Wolfram Kollatschny, lead study author and professor at the University of Göttingen, in a statement.
All three of the black holes can be found in the same region that’s less than 3,000 light-years across. For reference, the astronomers said this space is less than one hundredth the size of the whole galaxy.
“Up until now, such a concentration of three supermassive black holes had never been discovered in the universe,” said Peter Weilbacher, study author at the Leibniz Institute for Astrophysics Potsdam. “The present case provides evidence of a simultaneous merging process of three galaxies along with their central black holes.”
This discovery will allow astronomers to understand more about how galaxies evolve over time, especially the largest galaxies in the universe. Insight about how those galaxies formed has eluded researchers in the past, since their size couldn’t be explained by the types of interactions and mergers astronomers have observed in the past.
“If, however, simultaneous merging processes of several galaxies took place, then the largest galaxies with their central supermassive black holes were able to evolve much faster,” Weilbacher said. “Our observations provide the first indication of this scenario.”
Over time, likely a few million years, the three supermassive black holes will likely merge, the researchers said. This ultimate merger is expected to create incredibly strong gravitational waves, or ripples in space time.