Black hole
Because black holes are very hard to see, people find them by the way they affect other things near them. The place where there is a black hole can be found by tracking the movement of stars that orbit somewhere in space. Or people can find it when gas falls into a black hole, because the gas heats up and is very bright. This can be found by telescopes on Earth or by Earth-orbiting telescopes such as Chandra or XMM Newton. Inside a black hole the rules of physics are very different.<ref>Wald, Robert M. 1992. Space, time, and gravity: the theory of the Big Bang and black holes. University of Chicago Press. ISBN 978-0-226-87029-8</ref>