So far, all black holes discovered by astronomers fall into two broad categories: “stellar mass” black holes and “supermassive” black holes.
But what puzzles astronomers is why the two extremes – what about intermediate-sized black holes?
Black holes were predicted by Albert Einstein’s general theory of relativity. Their gravity is so strong that no material object, not even light, can escape from their vicinity.
Astronomers have only been able to obtain evidence for their existence in recent decades by studying black holes accreting (attracting) gas from nearby stars and finding fast-moving stars in the vicinity of black holes.
But since 2015 an exciting third way to detect black holes has become available: gravitational waves from merging black holes.
This article appeared on the Conservation on 20 February 2018. Its authors include Associate Professor Holger Baumgardt and Professor of Astrophysics Michael Drinkwater.
