• Question: How many black holes are there in space and are any close to our solar system?

    Asked by Emilie W to Claire on 7 Mar 2019.
    • Photo: Claire Greenwell

      Claire Greenwell answered on 7 Mar 2019:

      Hi! Good question. There are a lot of parts to this answer so bear with me!

      There are two main types of black hole. “Stellar mass” black holes are the more common ones. They are made when a large star collapses at the end of its life, and are about 10 times the mass of our Sun. These are quite common in our galaxy (and in other galaxies). The closest one is about 3000 light years away (for context, the closest star to us (other than the Sun!) is 4 light years away, and our galaxy is 180,000 light years across). So not very close, and not likely to come closer very soon! “Super massive” black holes are the ones I study. These are more like 1,000,000,000 times the mass of our Sun, and there is one at the centre of every galaxy (probably! we haven’t observed them all yet). So the closest one of those is at the centre of the Milky Way, about 25,600 light years from Earth. It’s called Sagittarius A*. As for how many there are: nobody really knows! The universe is really, really big: there are about as many super massive black holes as there are galaxies, which is billions. There are millions of the stellar mass black holes in our galaxy, and it’s likely there are similar numbers in every other galaxy – millions x billions.