Although black holes were a theoretical possibility ever since Karl Schwarzschild discovered the non-rotating solution in 1916, and considered by many to be a strong physical possibility following Robert Oppenheimer and Hartland Snyder's work in 1939, until 1963 there remained a strong school of opposition to the idea. In particular, there were those who believed that perturbations - and, in particular, those perturbations caused by rotation - would stop black hole horizons ever forming. Roy Kerr's dramatic discovery showed that this was not the case, and since rotating solutions with event horizons existed, black holes had to be taken very seriously as actual physical objects of the universe.

As with many major leaps in science, acceptance of the reality of astrophysical black holes was not immediate. It is ironic that the first observations of then mysterious quasars were discussed at the very same Texas symposium in 1963 where Roy first presented his results to a generally unreceptive audience. As the Kerr solution was explored further it came to be realised that supermassive Kerr black holes can explain the engines that power quasars, and also the gamma ray bursts resulting from the most violent supernovae.

The timeline of black hole physics

• 1915 - Albert Einstein writes down the field equations of GR

• 1916 - Karl Schwarzschild solves vacuum Einstein equations with spherically symmetric non-rotating systems

• 1918 - Hans Reissner & Gunnar Nordström solve the Einstein-Maxwell field equations for charged spherically-symmetric non-rotating systems

• 1923 - George Birkhoff proves that the Schwarzschild spacetime geometry is the unique spherically symmetric solution of the Einstein vacuum field equations

• 1939 - Robert Oppenheimer & Hartland Snyder show gravitational collapse of a pressureless homogeneous fluid sphere leads to formation of a trapped region

• 1963 - Roy Kerr solves the Einstein vacuum field equations for uncharged symmetric rotating systems

• 1964 - Roger Penrose proves that an imploding star will necessarily produce a singularity once it has formed an event horizon

• 1965 - Ezra Newman and collaborators solve the Einstein-Maxwell equations for charged rotating systems

• 1967 - Werner Israel presents proof of a "no hair" theorem at King's College in London

• 1968 - Brandon Carter uses Hamilton-Jacobi theory to derive 1st-order equations of motion for charged particle moving in external fields of Kerr-Newman black holes

• 1969 - Roger Penrose discusses the Penrose process for the extraction of the spin energy from a Kerr black hole

• 1969 - Roger Penrose proposes the cosmic censorship hypothesis

• 1971 - Identification of Cygnus X-1/HDE 226868 as a binary black hole candidate system

• 1972 - Stephen Hawking proves that the area of a classical black hole's event horizon cannot decrease

• 1972 - Jacob Bekenstein suggests that black holes have an entropy proportional to their surface area due to information loss effects

• 1973 - James Bardeen, Brandon Carter, and Stephen Hawking propose 4 laws of black hole mechanics in analogy with laws of thermodynamics

• 1973 - David Robinson completes the proof of the uniqueness theorem for Kerr black holes

• 1973 - Stephen Hawking applies quantum field theory to black hole spacetimes and shows that black holes will radiate particles with a black-body spectrum which can cause black hole evaporation

• 1989 - Identification of GS2023+338/V404 Cygni as a binary black hole candidate system

• 1997 - A team of astronomers led by Andy Fabian find evidence from redshifts of the innermost portions of accretion disks around supermassive black holes that the black holes are rotating

• 2000 - Astronomers present evidence for the hypothesis that Sagittarius A* is a supermassive black hole at the centre of the Milky Way galaxy

• 2001 - X-rays are detected from matter falling into the black hole in the centre of our galaxy

• 2002 - NASA's Chandra X-ray Observatory identifies double galactic black holes system in merging galaxies NGC 6240.

• 2003 - A team of astronomers led by Reinhard Genzel show that the supermassive black hole in the centre of our galaxy is spinning at about half the maximum rate allowed by the Kerr solution

Note: The time line uses modern terminology. The term "black hole" was coined by John Wheeler [1], being first used in his public lecture "Our Universe: the Known and Unknown" on 29 December, 1967. The terminology that "black holes have no hair" in respect of various uniqueness and "no hair" results, was also due to John Wheeler and was introduced in an article co-authored with Remo Ruffini in 1971 [2].

At the beginning of the Golden Age of Black Hole Physics, black holes were referred to as "frozen stars" or "gravitationally collapsed objects". The change in terminology in the late 1960s deeply reflects the paradigm shift that the discovery of the Kerr solution unleashed. It was realised over time that black holes not only do exist, but are far from being dead boring objects; they are highly dynamical. We now understand that they are very important to the formation of galaxies, and are a central feature of the life of the Universe.

References

1. J.A. Wheeler's lecture appeared in the Phi Beta Kappa Society journal The American Scholar (Vol. 37, no 2, Spring 1968); and in the Sigma Xi Society journal American Scientist, (Vol 56, no 1, Spring 1968, pp 1-20). The announcement page is reprinted in V.P. Frolov and I.D. Novikov, Black Hole Physics: Basic Concepts and New Developments, (Kluwer, Dordrecht, 1998), p. 5.
2. R. Ruffini and J.A. Wheeler, Physics Today 24, 30 (1971).