Galaxy cluster hidden by black hole brightness
A galaxy cluster has been discovered hiding in plain sight, obscured by the bright light from a supermassive black hole at its centre.
An artist’s impression of a supermassive black hole at the centre of a galaxy. Image Credit: NASA/JPL-Caltech
Astronomers have discovered a galaxy cluster that had been obscured by the bright light from its central supermassive black hole.
Previously only a lone supermassive black hole was thought to have existed.
The discovery revealed that the active supermassive black hole - known as a quasar - is so bright it obscures the light from hundred of galaxies around it.
A study of the galaxy cluster estimates there are hundreds of individual galaxies in the cluster, amounting to a mass totalling about 690 trillion Suns.
It is thought that the quasar at the centre of the cluster is 46 billion times brighter than our Sun.
This brightness is most likely caused by the black hole ‘feeding’ on infalling cosmic material.
A huge disc of material orbits the quasar, and big chunks of this material fall inwards, generating furious heat and light energy that is outshining the galaxies clustered around it, effectively hiding it from our view.
“This might be a short-lived phase that clusters go through, where the central black hole has a quick meal, gets bright, and then fades away again,” says Michael McDonald of MIT’s Kavli Institute for Astrophysics and Space Research, who led the study.
“This could be a blip that we just happened to see. In a million years, this might look like a diffuse fuzzball.”
The discovery could point to other galaxy clusters obscured from view because of the brightness of their central supermassive black holes.
It was thought that this black hole was simply a lone object in space, so perhaps other ‘lone’ objects are actually obscuring their surroundings with intense bright light.
The discovery was made through a survey called CHiPS (Clusters Hiding in Plain Sight), which was set up by the study authors to look once again at X-ray images taken in the past.
Looking for very bright objects in the sky, the team then went back to study these light sources using the Magellan Telescope in Chile.
If they found a large number of galaxies surrounding the quasar, this was considered a sign that it could be a hidden galaxy cluster.
The team then observed the source using the Chandra X-ray Observatory.
“Some 90 percent of these sources turned out to not be clusters,” McDonald says. “But the fun thing is, the small number of things we are finding are sort of rule-breakers.”
“The brightness of the black hole might be related to how much it’s eating,” McDonald says.
“This is thousands of times brighter than a typical black hole at the center of a cluster, so it’s very extreme in its feeding. We have no idea how long this has been going on or will continue to go on.
“Finding more of these things will help us understand, is this an important process, or just a weird thing that there’s only one of in the Universe.”
Iain Todd is BBC Sky at Night Magazine's Staff Writer. He fell in love with the night sky when he caught his first glimpse of Orion, aged 10.