# What would happen if two black holes collided?

#### Sniperman724

What would happen if two super-massive black holes collided with each other? I know it may be a very unlikely scenario.
Thanks!

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#### qraal

The surface area of the holes is conserved. When they collide the difference in mass-energy implied by that is released, mostly as gravity waves.

To see why, consider two black-holes of mass 1, radius 1 and thus area 1. Total area is 2, but a black hole of mass 2 has an area of 4, because the radius scales linearly with the mass, but the area with the square of the radius. To get an area of two the radius is sqrt(2) and the proportion of mass radiated away as energy is (1-sqrt(2)/2) = 0.293. Being nearby the collision of two super-massive black-holes would be incredibly unhealthy...

#### Nabeshin

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