A black hole is a spot in space where gravity pulls so much that even light can not get out. The gravitational force is extremely strong because the matter has been compressed into a tiny space. This can occur when a star is dying. Because no light can get out, people can’t see black holes through naked eyes. They are transparent. Only specialized space telescopes can spot the black holes. These telescopes can provide details on how stars that are very close to black holes act otherwise than other stars.