The extensively studied galaxy NGC 6240 – located about 300 million light-years away from Earth – was previously thought to have acquired its odd shape in the process whereby two distinct galaxies merged into one, leaving two supermassive black holes at the place of collision.
This, however, had recently turned out to be wrong. Although not completely wrong, and certainly wrong in an exciting way – NGC 6240 was found to actually contain as many as three supermassive black holes fighting for position near its centre.
“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 lead author Professor Wolfram Kollatschny from the University of Göttingen.
The discovery was made using European Southern Observatory’s (ESO) Very Large Telescope (VLT) and 3D-mapping techniques, suggesting that each of the black holes has a weight of roughly 90 million Suns (as compared to the 4 million solar mass equivalents of Milky Way’s own supermassive black hole Sagittarius A*).
Even more interestingly, all three of the celestial bodies are located in a region less than 3,000 light-years across, or less than on per cent the overall size of their home galaxy.
According to co-author Peter Weilbacher of the Leibniz Institute for Astrophysics Potsdam, although this is not the first time that astronomers have identified galaxies and their black holes heading on a collision course, “such a concentration of three supermassive black holes had never been discovered in the universe” ever before.
While bizarre and interesting in their own right, these findings also show how multiple galaxies can smash into each other, thereby forming even larger ones, which is an issue that has mystified astronomers for decades due to the inadequacy of explaining the formation of the universe’s biggest galaxies via slow, two-galaxy mergers.
“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.”