From Science.KQED: In 1964, a rocket-born probe peaking at space from just outside of Earth's atmosphere detected intense X-ray emissions coming from a spot in the constellation Cygnus. Designated Cygnus X-1, this location earned the distinction of being the first probable detection a black hole. The X-rays were explained as coming from the gases of a nearby companion star being pulled off and swallowed up, heating up to a searing X-ray glow before disappearing into the black hole.