Two physicists made a bet over whether this object was actually a black hole
Cygnus X-1, an X-ray source discovered in the 1960s, became the first object widely accepted as a real black hole, based on its mass and the way it pulled material from a companion star. Stephen Hawking was skeptical enough to make a wager against it with fellow physicist Kip Thorne in the 1970s, betting on the losing side as a kind of insurance against his own life's work. By 1990, with better data in hand, Hawking conceded the bet.