Of the almost countless galaxies already recorded, NGC 6240 has appear almost unique due to its strange shape and unusual infrared brightness. This was believed to be the result of two galaxies colliding – until now.
Astronomers more than 30 years ago reported evidence of a double active nucleus, with a brace supermassive black holes sitting at NGC 6240’s centre.
But researchers now believe they have found a third supermassive black hole at its core.
This new finding shows three galaxies are actually in the process of combining, with each bringing its own supermassive black hole galactic nucleus to the region 300 million light years from Earth.
Professor Dr Wolfram Kollatschny from the University of Göttingen, said: “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.”
The resulting images revealed three nodes sitting at NGC 6240’s, one northern component and two southern.
However, the latest discovery does not mean the research was wrong.
The new evidence instead suggests only two of the black holes are actively accreting matter, while the newly-discovered one is dormant.
Each of the supermassive black holes are believed to be more than 90 million times the mass of the Sun.
To put this in cosmic context, our galaxy’s supermassive black hole, Sagittarius A*, is a mere 4 million solar masses.
All three of those in NGC 6240 are locked in an orbit in an area less than 1 kiloparsec across (3,260 light-years).
The two southern black holes are separated by a distance of just 198 parsecs (645 light-years).
The trio are slowly spiralling inward towards each other.
Dr Peter Weilbacher of the Leibniz Institute for Astrophysics, said: “Such a concentration of three supermassive black holes has so far never been discovered in the Universe.
“The present case provides evidence of a simultaneous merging process of three galaxies along with their central black holes.”
Earlier this year another triple merger was discovered, with three supermassive black holes caught in the process of spiralling into the centre of galaxy SDSS J084905.51+111447.2.
However, that system featured significantly larger separations between, with distances stretching on average 10 kiloparsecs (32,600 light-years).