1687 Sir Isaac Newton Described gravity in his publication, "Principia."
1783 John Michell Conjectured that there might be an object massive enough to have an escape velocity greater than the speed of light.
1796 Simon Pierre LaPlace Predicted the existence of black holes. "...[It] is therefore possible that the largest luminous bodies in the universe may, through this cause, be invisible." -- Le Système du Monde
1915 Albert Einstein Published the Theory of General Relativity, which predicted spacetime curvature.
1916 Karl Schwarzchild Used Einstein's Theory of General Relativity to define a black hole. Defined gravitational radius of black holes, later called the Schwarzchild radius.
1926 Sir Arthur Eddington Relativity expert who, along with Einstein, opposed black hole theory.
1935 Subrahmanyan Chandrasekhar Pioneer in theory of white dwarfs that led to an understanding of mass limits that decide whether a star will die as a white dwarf, neutron star or black hole.
1964 John Wheeler Coined the term, "black hole."
1964 Jocelyn Bell-Burnell Discovered neutron stars that, at the time, were the densest matter found through observations.
1970 Stephen Hawking Defined modern theory of black holes, which describes the final fate of black holes.
1970 Cygnus X - 1 The first good black hole candidate that astronomers found. It emits x-rays and has a companion smaller than Earth but with a mass greater than that of a neutron star.
1994 Hubble Space Telescope Provides best evidence to date of supermassive black holes that lurk in the center of some galaxies. The Space Telescope Imaging Spectrograph (STIS) revealed large orbiting velocities around the nucleus of these galaxies, suggesting a huge mass inside a very small region.