Although the discussions of the capture of light by massive objects can be dated to John Mitchell and Pierre Simon Laplace in the eighteenth century, a proper understanding lies in the realms of general relativity theory.
Karl Schwarzschild calculated the boundary radius or event horizon, of such a theoretical (nonrotating) body to be about 3 km for a body of one solar mass.
Interior to the event horizon relativity theory suggests that any matter collapse into an infinitesimally small volume or singularity.
In 1963, a solution for a rotating object was provided by Robert P. Kerr. Stephen W. Hawking in the 1970s applied quantum mechanical concepts to the theory of black holes to show that they may not exist forever but can radiate energy.
To address the physical origin for black holes, J. Robert Oppenheimer and Hartman Snyder in 1939 first considered the collapse of a star.
Modern astronomy inquiry identifies two observational classes or black holes candidates, stellar black holes in X-ray binary systems and massive black holes on the nuclei of galaxies.
A dozen or more black hole candidates are known, including Cygnus X-1 and ScorpionX-1. The second category, a few million to a few billion solar masses, is postulated as the central engine responsible for a wide range of energetic phenomena (radio, X-ray, and gamma-ray emission, jets and others) associated with the nuclei of some galaxies.
Such active galactic nuclei objects include Seyfert galaxies, radio lobe galaxies, and quasars. Massive black holes also may be present in the centers of some nonactive galaxies.
What is a Black Hole is space?