A galaxy’s core is a busy place, crowded with stars swarming around an enormous black hole. When galaxies collide,  two black holes spiral toward each other, merging to make an even bigger gravitational monster.

Once it is created, the monster goes on a rampage. The merger kicks the black hole into surrounding stars. There it finds a hearty meal, shredding and swallowing stars at a rapid clip.

Before the merger, as the two black holes whirl around each other, they stir the galactic center like the blade of a blender. Their strong gravity warps space, sending out ripples known as gravitational waves. When the black holes merge, they emit gravitational waves more strongly in one direction. That inequality kicks the black hole in the opposite direction like a rocket engine……..

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