Shall we dance? Two big black holes found together

By Will Dunham

WASHINGTON (Reuters) - Two colossal black holes appear to be orbiting one another in sort of a cosmic minuet at the centre of a faraway galaxy formed when two separate galaxies collided, U.S. astronomers said on Wednesday.

These two so-called supermassive black holes, which are celestial objects with enormous gravitational pull, are locked in orbit about 5 billion light years away from Earth, the scientists said. A light year is about 6 trillion miles (10 trillion km), or the distance light travels in a year.

Data from Apache Point Observatory in New Mexico provided the best evidence to date of two black holes orbiting each other, according to astronomer Todd Boroson of the National Optical Astronomy Observatory in Tucson, Arizona.

This is known as a binary system.

Scientists believe all or most galaxies have supermassive black holes at their centre. For example, our Milky Way galaxy has a black hole at its centre that is about 3 million times the mass of the sun.

When galaxies collide and merge, as they do relatively often, the black holes at their centre may gravitate towards one another because of their great mass, entering into orbit as these two appear to be doing.

Boroson said orbiting black holes eventually may merge into an even larger single black hole.

While scientists think binary black holes may be relatively common, they have been elusive.