BLACK holes really do come in all sizes: last week, astronomers announced strong evidence that certain bright X-ray sources in the sky are indeed “intermediate-mass” black holes, hundreds of times the mass of our Sun. But their origins remain a puzzle.
We know of several small black holes in our Galaxy, similar in mass to our Sun, as well as monster black holes of up to a billion solar masses that live in the centres of galaxies. But until now we did not know whether it was possible to have black holes of any size in between.
Although we cannot…
