History of understanding of the interior structure of black holes

1915-1963  Schwarzschild rules.
1963  Kerr discovers what turns out to be the solution for a rotating black hole. Shortly thereafter Newman et al. generalize to the case of a charged rotating black hole.
1965  Penrose proves the first of a series of Penrose-Hawking singularity theorems.
Under plausible conditions (causality, a positive energy condition), a spacetime containing a trapped surface is “geodesically incomplete”.
1967  Penrose points out that observers reaching the “Cauchy horizon” of a charged (Reissner-Nordström) or rotating (Kerr-Newman) black hole will see the outside universe infinitely blue-shifted
Ž RN and KN solutions must break down at the Cauchy horizon.
1980s  Speculations (e.g. Novikov & Starobinsky, Gibbons) that RN and KN solutions may overcome their internal problems with quantum mechanics.
1990  Poisson & Israel, in a seminal paper, clarify the nature of the instability at the Cauchy horizon. They show that, if “ingoing” (E > 0) and “outgoing” (E < 0) streams are simultaneously present near the inner horizon, then relativistic counter-streaming between the two streams will lead to “mass inflation”, in which the interior mass M(r) (a gauge-invariant scalar quantity) exponentiates to huge values. The instability is purely classical (not quantum mechanical).
1990+  Most of the literature on the interior structure of black holes focuses on mass inflation. The main result is that the end state of an isolated charged or rotating black hole is that it contains a null singularity at finite radius along the erstwhile Cauchy horizon, in addition to a central spacelike singularity.
Comment  Since mass inflation depends on the simultaneous presence of both ingoing and outgoing fluids near the inner horizon, computations that assume a single fluid are of suspect validity as models of the interior structure of black holes.

  Mass Inflation