The Black Vault

Black holes: a galactic vacuum cleaner.

A PAIR of Melbourne astronomers have overturned a decade-old theory on how supermassive black holes grow and, in the process, identified the location of a missing population of medium-sized black holes.

For years astronomers thought supermassive black holes, which are found at the centre of galaxies, grew by consuming gas clouds at a constant rate relative to the growth of nearby stars.

Black holes are celestial objects with a gravitational field so strong that virtually nothing can escape them.

Astronomer Alister Graham said the gigantic dense bodies, with masses many millions of times that of our sun, were believed to comprise a small fraction - 0.2 per cent - of the surrounding galaxy's total mass.

''We thought if we knew how big the galaxy was, then we knew how big the black hole would be,'' said Professor Graham, from the Centre for Astrophysics and Supercomputing at Swinburne University of Technology.

''But everybody had those relationships wrong.''