Galactic train wreck: Astronomers spot three supermassive black holes merging together at the centre of a galaxy 300 million light-years away
- Galaxy NGC 6240 stands out for its unusual shape and infrared brightness
- Now scientists have discovered a third supermassive blackhole is in the centre
- Spectroscopic observations from the MUSE 3D spectrograph spotted the third
A misshapen galaxy previously believed to be the result of two supermassive black holes colliding has been found by researchers to be hiding a third supermassive black hole at its core.
NGC 6240 has always stood out for its unusual shape and striking infrared brightness, with astronomers reporting evidence of a double active nucleus in 1983 – meaning two active supermassive black holes at its centre.
Now, thanks to very high resolution spectroscopic observations from the MUSE 3D spectrograph in Chile, researchers have been able to distinguish what sits in the centre of the bright light emitted by the galaxy 300 million light-years away – three supermassive black hole galactic nuclei.
Astrophysicist Wolfram Kollatschny from the University of Göttingen in Germany 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 position of the three black holes remains unknown due to their proximity and the bright light obscuring them.
NGC 6240 has always stood out for its unusual shape and striking infrared brightness
Dr Kollatschny and his team used the MUSE 3D spectrograph mounted on the European Southern Observatory’s eight-metre Very Large Telescope in Chile to take the pictures of the triplet blackholes.
Of the three supermassive blackholes seen – one in the northern component and two in the southern – only two of them appear to be actively pulling in matter, while the third is dormant.
Each weigh around 90 million times the mass of the sun. The Milky Way’s supermassive black hole, named Sagittarius A* only weighs 4 million solar masses in comparison.
The two southern black holes are seen to be just 645 light-years (198 parsecs) apart, all three orbiting in a small area just 3,260 light-years across (1 kiloparsec).
Astrophysicist Peter Weilbacher of the Leibniz Institute for Astrophysics Potsdam in Germany 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.’
Another triple merger was discovered earlier this year at the centre of a galaxy called SDSS J084905.51+111447.2. However the three supermassive black holes are much further apart, around 10 kiloparsecs as they are in an earlier stage of their ‘merger’ a process which takes around a billion years.
Images taken by the high resolution MUSE 3D spectrograph in Chile
When the galaxies merge they will prove or disprove what is theoretically known as the final parsec problem.
Scientists have a theoretical problem understanding how supermassive black holes could merge together – as the galaxies are drawn together they transfer their orbital energy to the gas and stars around them and begin to orbit in an increasingly tight spiral.
As their orbits shrink they have a smaller region of space which they can transfer energy to.
This means by the time they reach 3.2 light-years apart theoretically the energy being emitted would not be able to be absorbed by the space that surrounds them – leading them to remain in a stable binary orbit for billions of years, a balance known as ‘the final parsec problem’.
Scientists believe the presence of a third blackhole could provide the extra umph needed for the objects to close the gap.
But for now the problem remains theoretical as the three supermassive blackholes at the centre of NGC 6240 won’t close for another one to two billion years.
Gravitational waves that scientists believe the black holes are creating, but are currently undetectable, may help us understand how to detect black holes in future and solve the parsec problem.
The research has been published in Astronomy & Astrophysics.
WHAT’S INSIDE A BLACK HOLE?
Black holes are strange objects in the universe that get their name from the fact that nothing can escape their gravity, not even light.
If you venture too close and cross the so-called event horizon, the point from which no light can escape, you will also be trapped or destroyed.
For small black holes, you would never survive such a close approach anyway.
The tidal forces close to the event horizon are enough to stretch any matter until it’s just a string of atoms, in a process physicists call ‘spaghettification’.
But for large black holes, like the supermassive objects at the cores of galaxies like the Milky Way, which weigh tens of millions if not billions of times the mass of a star, crossing the event horizon would be uneventful.
Because it should be possible to survive the transition from our world to the black hole world, physicists and mathematicians have long wondered what that world would look like.
They have turned to Einstein’s equations of general relativity to predict the world inside a black hole.
These equations work well until an observer reaches the centre or singularity, where, in theoretical calculations, the curvature of space-time becomes infinite.