The conversation between human and AI assistant.
[|Human|] Summarize the characteristics of a black hole.
[|AI|] A black hole is an extremely dense celestial object with gravity so strong that nothing, not even light, can escape it. Its immense gravity is caused by a large amount of matter compressed into a very small space. It is invisible, but its presence can be inferred from its effects on nearby matter, such as stars orbiting around it. The boundary around a black hole from which no escape is possible is called the event horizon. Time and space behave in strange ways near a black hole, with time slowing down and distances becoming distorted. Black holes are thought to form from the remnants of massive stars that have collapsed onto themselves at the end of their lives.
[|Human|] 
Summarize the characteristics of a black hole.