What would happen if two black holes collided?

What happens when an unstoppable force meets another unstoppable force…


Asked by Chris Howlett

Scientists believe that the interaction of two black holes could have one of two outcomes. The first is that they merge together to form one, much more massive black hole. The second is that due to spin, the two black holes could interact and recoil from each other sending one hurtling away.

We do now have evidence that the second option has happened. We believe that at the centre of large galaxies there resides a supermassive black hole containing hundreds of millions of times the mass of our Sun. These supermassive black holes are thought to be spinning at phenomenal rates, and so as two galaxies collide, their black holes will eventually interact. And scientists at the Max Planck Institute for extraterrestrial Physics have observed a black hole being ‘kicked out’ of its parent galaxy through interacting with a bigger black hole. We can effectively think of it as two spinning tops. Depending on the rate of their spin, their size and the angle at which they collide, they could come together, or one can get spun out of the way of the other. While both options are possible, we thus far only have evidence of the second, more extreme of these options.

Image courtesy of the Max Planck Institute for Extraterrestrial Physics

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