DANCING BLACK HOLE TWINS SPOTTED

A giant amalgam of black holes sits at the centre of the Virgo galaxy cluster

Reseachers have seen the best evidence yet for a pair of black holes orbiting each other within the same galaxy.

While such "binary systems" have been postulated before, none has ever been conclusively spotted.

The new black hole pair is dancing significantly closer than the prior best binary system candidate.

The work, published in the journal Nature, is in line with the theory of growth of galaxies, each with a black hole at its centre.

The theory has it that as galaxies near each other, their central black holes should orbit each other until merging together.

But evidence for black holes nearing and orbiting has so far been scant.

As matter falls into black holes, it emits light of a characteristic colour that in turn gives information about the direction in which the black hole is moving.

Because they are orbiting each other, astronomers have suggested that binary black hole systems would emit two beams, each a slightly different colour.

Todd Boroson and Tod Lauer of the National Optical Astronomy Observatory analysed some 17,500 spectra from the Sloan Digital Sky Survey, and found such a pair coming from a distant quasar.

The researchers estimate that the two light sources come from black holes between 20 million and one billion times heavier than the sun.

The black holes are separated by an estimated distance of less than a third of a light-year - cheek-to-cheek by black hole standards and significantly more than the postulated binary system spotted by the Chandra X-ray Observatory in 2003.

The pair are estimated to dance around one another every 100 years.

Because they are moving with respect to the Earth as well as to each other, observations of their movement over the next few years could prove that they are in fact the first partnered pair of black holes.

"Previous work has identified potential examples of black holes on their way to merging, but the case presented by Boroson and Lauer is special because the pairing is tighter and the evidence much stronger," said Jon Miller, an astronomer at the University of Michigan.
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