Which celestial object is thought to be a black hole in orbit around a supergiant star?

Cygnus X-1 is well-known as a binary star system that contains a black hole orbiting a supergiant star. The system has been studied extensively, and strong evidence supports the presence of a black hole due to the immense gravitational effects it has on the nearby supergiant star, which is classified as a blue supergiant known as HDE 226868.

The mass of the black hole is estimated to be between 15 to 20 times that of the Sun, indicating that it is a stellar-mass black hole formed from a massive star's collapse. Observable phenomena in Cygnus X-1, such as X-ray emissions from material falling into the black hole, further confirm its identity as a black hole in a close relationship with a massive star.

Other options listed, such as M1 (the Crab Nebula), Cas A (Cassiopeia A), and NGC 6888 (the Crescent Nebula), do not involve black holes in orbit with a supergiant star. Instead, these are remnants of supernovae and nebulae, which do not have the characteristics associated with black hole systems. Thus, Cygnus X-1 stands out as the specific example of a black