How and when were black holes discovered?

Answer 1

Black holes were described theoretically before evidence for their existence was collected from astronomical observations. The philosopher and geologist John Michell in the late 18th century described what would happen to infalling matter approaching a body of a certain mass where it had sufficient acceleration from gravity to approach the speed of light, and proposing the idea that light theoretically emitted by it would be unable to escape; but it wasn't until Einstein's General theory of Relativity (1915) that the framework of gravitation was in place and the reality of black holes could be described mathematically. Building upon Einstein's work, the effect of gravity on space was much better understood and solutions to his field equations yielded much more accurate models of black holes' properties and reinforced the theoretical evidence for their existence. Observational evidence came later, but because black holes cannot emit light, the evidence was indirect, in the form of certain x-ray sources, relativistic jets, quasars or galactic nuclei, and orbital motion near massive bodies. Credit for discovery of the first strong black hole candidate through astronomical observation in an X-ray binary system (Cygnus X-1) goes to Bolton, Murdin, and Webster in 1972.

Answer 2

Black holes were first theoretically predicted by physicist Karl Schwarzschild in 1916 based on Einstein's theory of general relativity. The first potential black hole candidate was discovered in 1964 by Maarten Schmidt and was later confirmed in the 1970s through observations of X-rays emitted by matter falling into black holes.