Cosmic collisions ‘aren’t responsible for black hole growth’

WASHINGTON - A new study has revealed that cosmic collisions, which have been believed to be the culprit behind increasing growth of black holes, are not to blame.

When black holes are formed, they absorb great amounts of light, which then shines brightly as it falls towards oblivion. This results in the telltale bright spots at the centre of galaxies known as active galactic nuclei (AGN).

“You can usually tell when galaxies have been involved in a merger. Instead of the neat, geometric spiral or smooth elliptical shapes you usually see in Hubble images, colliding galaxies typically look distorted and warped,” said Knud Jahnke, co-author of the study.

Team leader Mauricio Cisternas from Germany’s Max Planck Institute for Astronomy, and his team set up a kind of identity parade of galaxies, in which he had modelled and removed the bright spot that reveals the AGN.

Astronomers compared 140 active galaxies with a control group of over 1200 comparable inactive galaxies and found that there has been no significant link between AGN activity and galactic mergers for at least the past eight billion years.

The conclusion to be derived, therefore, is that other phenomena such as instabilities within galaxies, collisions of molecular clouds or tidal disruption by other galaxies flying by must be to blame.

The next question the group is gearing up to address is if there could still be a causal connection between mergers and activity in the more distant past.

The results will be published in the Astrophysical Journal on 10 January. (ANI)