# Stellar Black Hole

One of the possible evolutionary endpoints of high mass stars. Stellar black holes have masses <100 Msun. Once the core of the star has completely burned to Fe, energy production stops and the core collapses resulting in a supernova explosion. If the core is greater than ~2.3 Msun, the maximum mass of a neutron star, collapse continues and a stellar black hole is formed. These black holes are generally modeled as Kerr black holes, because the original rotation of the massive star would be conserved during the collapse. Stellar black holes are therefore most easily discovered in X-ray binary systems, where gas from a companion star is being pulled into the black hole. X-rays are produced by this gas which is heated to ~107 K as it spirals towards the black hole via an accretion disk. The mass of the black hole, typically 3–20 Msun, by observing its gravitational effect on the companion star.

About 20 X-ray binary systems are thought to contain stellar black holes. One of the best candidates is LMC X-3 in the Large Magellanic Cloud. Here the x-ray source is associated with a main sequence B3 star whose shape has been severely distorted by the gravitational field of its companion. The binary system has an orbital period of 1.7 days. The mass of the compact object probably is considerably higher than >3 Msun. The Cygnus X-1 binary system, discovered in 1965, consists of a O9.7 Iab type supergiant and a compact object orbiting with a period of 5.6 days. The mass of the unseen companion is ~10 Msun. Cygnus X-1 is one of the brightest X-ray sources in the sky. A jet from the Cygnus X-1 source has ionized the interstellar medium, producing a spectacular bubble-like x-ray feature.

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