A stellar black hole is a type of black hole formed by the gravitational collapse of a massive star at the end of its life cycle. These black holes typically have masses ranging from about 3 to several dozen times the mass of the Sun. They are distinguished from supermassive black holes, which reside at the centers of galaxies and have masses millions to billions of times that of the Sun, and from intermediate-mass black holes, which have masses in between stellar and supermassive categories.
Stellar black holes are predicted by the theory of general relativity and are believed to form when a massive star, usually more than 20 solar masses, exhausts its nuclear fuel. Without outward pressure from fusion to counteract gravity, the core collapses. If the remnant core exceeds the Tolman–Oppenheimer–Volkoff limit (estimated at around 2–3 solar masses), it collapses into a black hole.
Observable stellar black holes are typically detected indirectly through their interaction with surrounding matter. In binary star systems, a stellar black hole may accrete material from a companion star, forming an accretion disk that heats up and emits X-rays. Objects such as Cygnus X-1 are among the first and best-known astrophysical candidates for stellar black holes.
Stellar black holes may also be detected through gravitational wave signals produced when two such black holes merge. The first direct detection of gravitational waves, observed by the LIGO collaboration in 2015 (GW150914), confirmed the existence of binary systems containing stellar black holes.
Formation, mass distribution, and population estimates of stellar black holes are active areas of research in astrophysics. Accurate information is not confirmed regarding their exact formation channels in all stellar environments, including the role of metallicity and stellar rotation.
Stellar black holes do not possess electric charge or significant magnetic fields of their own, and their properties are generally described by mass and angular momentum (spin), consistent with the no-hair theorem.