In 1971, two astronomers proposed x-ray source Cygnus X-1 might be a black hole. This is the first object to be nominated for being a black hole.

If further investigations proved Cygnus x-1 was not a black hole, Stephen Hawking would be very disappointed because he had done so much work on black holes.

In 1974, Stephen Hawking bet Kip Thorne that Cygnus x-1 was not a black hole. Then if Cygnus x-1 turned out not to be a black hole, Hawking would at least have won a bet.

In 1990, enough evidence had finally accumulated that Kip Thorne conceded and Hawking won the bet. Cygnus x-1 is a black hole.