As celestial entities go, black holes are, paradoxically, both commonplace and extraordinary. They could be seen as commonplace due to their general ubiquity. Astrophysicists now believe that giant black holes ?" each with the mass of millions or billions of suns ?" inhabit the centres of practically every large galaxy, where they exert a powerful influence over star formation and other processes. There are more than 200 billion such galaxies, according to estimates, each thought to harbour about 100 million stellar- or star-sized black holes. Adding that up, we're talking about something on the order of 1019 ?" or 10 billion billion ?" black holes. And far into the future, when the Universe is three times its current age (or about 40 billion years old), black holes will be all that's left. That prediction was made in an analysis by the astrophysicists Fred C Adams and Gregory Laughlin in 1997 who concluded that, in the distant future, 'the only stellarlike objects remaining