Binary black hole

A binary black hole is two black holes that are very close together or even connected by a special string of matter. Black holes are special places in the universe where a lot of mass has been packed into a very small area - so small and with so much mass that not even light can escape. Binary black holes happen when two smaller black holes are not just close together, but actually touching in the same spot out in space. This can cause some pretty big and wild effects, like really powerful gravitational waves (ripples in space-time) that can be detected here on Earth.