Shock singularity
In general relativity, the shock singularity, also called the shockwave singularity, the Marolf-Ori singularity, or the outflying singularity, is a null singularity propagating out of the outgoing section of the inner horizon of a spinning or charged black hole that effectively manifests as a gravitational shockwave. Perturbations to the inner horizon result in abrupt changes in the amplitude of perturbing fields and the metric tensor itself, manifesting as an effective shockwave for sufficiently late-infall observers. The singularity was first described in 2012 by Donald Marolf and Amos Ori for classical Reissner-Nordström and Kerr black holes. It was numerically confirmed for the spherical charged case in 2016 by Ehud Eilon and Amos Ori.
Properties
The shock singularity is manifested by a sudden discontinuity in the metric tensor, caused by the capture of perturbations by previously in-falling radiation scattered outward by spacetime curvature. An object encountering the singularity would undergo a sudden, dimensionless tidal deformation followed by rapid acceleration to relativistic velocities towards the center of the black hole. The deformation could also be oscillatory. Some infallers may also experience a BKL-type singularity.The shock sharpens exponentially for later infall times. Although the shockwave is only truly experienced by late-infall observers, early-infall observers still experience shock-like behavior. This shock sharpening still appears in more realistic black hole models that take into account the black hole's accretion of dust and radiation; the shock in fact sharpens even more rapidly in these cases.