The Chandra X-ray Observatory, says, that over the last 13 years, it has identified 26 black holes in the Andromeda galaxy – sister to the Milky Way. See www.dailygalaxy.com/my_weblog/2013/06/26-new-black-holes-found-in-androm…
The same story is at http://phys.org/print290329260.html … where we learn that to classify them as black holes astronomers had to tick a certain special characteristic, two distinct features. One of these was they had to be brighter enough to contain a certain high level of X-rays and two, they also had to have a particular X-ray colour – in order not the mix them up with neutron stars, the dense cores of dead stars.