Article Posted on : - Oct 26, 2011

LONDON (PTI): Collisions between two galaxies may explain why super massive black holes form develops in them, according to a new research.

It's been known for some time that super massive black holes are usually found in the most massive galaxies, and that their size is proportional to the "bulge" in the centre of the galaxy -- that is the mass of the stars in the middle.

A new survey by an international team headed by Dr John Silverman of the University of Kashiwa, Japan, hints that the holes grow when two galaxies "collide", the Daily Mail reported.

The team used X-ray scans from NASA's Chandra observatory to identify galaxies with a growing super massive black hole -- the huge objects often release X-rays in their growth stages, and X-rays shoot straight through star-forming regions to give a clear picture of the number of the black holes.

The team's report, published in the Astrophysical journal, said that galaxies in close pairs -- as measured by the Cosmos redshift survey from the European Southern Observatory's Very Large Telescope -- are twice as likely to harbour super massive black holes.

But the mystery isn't fully solved.

Interactions between galaxies are fairly rare, and the team estimated that only around 20 per cent of the mass of black holes can be accounted for by these collisions.

Something else is causing the black holes to grow -- perhaps the final stages of galaxies coalescing into one, the researchers said.

What is certain is that the process takes an enormous amount of time, they added.

Super massive black holes sit at the hearts of most of the galaxies we can observe from earth, and astronomers believe there is one at the centre of our own galaxy, the Milky Way.