Original URL: http://www.theregister.co.uk/2004/03/30/andromeda_galaxy_home_to_ten/

Andromeda galaxy home to ten black holes

Massive neutron stars could be sun-sucking monsters

By Lucy Sherriff

Posted in Science, 30th March 2004 15:29 GMT

Astronomers have discovered ten possible black holes in the Andromeda Galaxy after scanning the area for a particular X-ray emission signature peculiar to the phenomenon.

Joint research teams at the Open University and the University of Leicester made the discoveries using the European Space Agency's XMM-Newton orbiting X-ray observatory to examine double star systems known as low mass X-ray binaries (LMXB).

These LMXB systems consist of a neutron star paired with a star similar to our own. The dense neutron star sucks in material from its neighbouring star, causing a huge heating effect and X-ray emissions.

The astronomers examine these emissions for clues about the mass of the neutron star. If it is sufficiently massive, it will collapse in on itself to form a black hole. The rate at which material spirals into the neutron star - coupled to the the system's luminosity - can provide evidence of this. If the neutron star is more than three times as massive as our sun, it is likely to be a black hole.

Dr Barnard, who led the research at the Open University commented: "Black holes are elusive beasts. We can never see them directly, only the effects they have on the stars and gas around them. But if black holes exist, the ten X-ray sources we have singled out are very likely black holes."

The new detection technique has allowed astronomers to identify these Andromedan black hole candidates in a very short time period: just 18 months. Searches for potential black holes in our own galaxy have turned up ten candidates too, but these were identified over several decades, rather than months. ®