A powerful jet from a supermassive black hole is blasting a nearby galaxy in the system known as 3C321 (Image: (NASA/CXC/CfA/D.Evans et al.; Optical/UV: NASA/STScI; Radio: NSF/VLA/CfA/D.Evans et al., STFC/JBO/MERLIN)

Massive black holes may be kicking the life out of galaxies by ripping out their vital gaseous essence, leaving reddened galactic victims scattered throughout the universe. While the case is not yet closed, new research shows that these black holes have at least the means to commit the violent crime.

It was already known that “supermassive” black holes at the centre of most galaxies sometimes emit vast amounts of radiation. But nobody had a good idea how common such violence is. A snapshot of the universe doesn’t give enough information to judge this because the activity of the black holes is thought to be intermittent, depending on how much nearby matter they have to feed on.

Now a team of astronomers have compiled a chronicle of activity going back deep into cosmic history, using the orbiting Chandra telescope to spot X-rays emitted by the black holes together with images from Hubble to look at their host galaxies. Previous surveys with less sensitive instruments were unable to spot the distant faint sources picked up by Chandra and Hubble. The team now have a set of galaxies reaching 13 billion light years.


The team calculate that at least a third of all big galaxies have contained a supermassive black hole emitting at least 10 billion times as much power as the sun, typically for as much as a billion years.

No more babies

Such violence releases enough energy to heat up galactic gas and even blast it right out of the galaxy. Stars are only born in clouds of cool gas, so you end up with a galaxy that is effectively dead, dominated by old red stars instead of the bright blue young stars that grace a “living” spiral galaxy like the Milky Way.

The black holes could be responsible for many of the dead, red galaxies seen in the universe. Most red galaxies are thought to be created when galaxies collide, which could help to feed the central black holes of the merging galaxies, switching on their deadly X-ray emissions. Violent black holes could also explain the existence of isolated lens-shaped galaxies, which do not seem to have suffered major collisions.

Still, it remains unknown how much power the black hole actually channels into galactic gas, says team member Asa Bluck of the University of Nottingham, UK. “So we have not proved that this is the dominant galaxy killer,” he told New Scientist. “But it is now the prime suspect in most cases of galaxy death.”

The research was presented at the Royal Astronomical Society National Astronomy Meeting in Glasgow, UK.