The constellation Cygnus gives Cygnus X-1 the first part of its name.
Cygnus X-1 is an X-ray binary system located in the constellation Cygnus, the Swan. Its name follows a common astronomical naming pattern: “Cygnus” identifies the constellation, while “X-1” indicates that it was the first strong X-ray source cataloged in that constellation. The system lies roughly 6,000 light-years from Earth.
Cygnus X-1 contains a blue supergiant star orbiting a stellar-mass black hole. Gas pulled from the star forms an accretion disk around the black hole, heating to millions of degrees and producing intense X-rays. Those X-rays made the system detectable even though the black hole itself is invisible.
Cygnus X-1 became historically important in the early 1970s, when observations strongly supported the idea that its unseen companion was a black hole. In 1974, Stephen Hawking famously lost a playful wager to Kip Thorne after accepting the evidence for the system’s black-hole nature.
A common mistake is to treat “X-1” as part of the constellation’s name. It is a source-designation suffix; Cygnus is the constellation name, while X-1 identifies the cataloged X-ray source.