Null Singularity Formation by Scalar Fields in Colliding Waves and Black Holes

TL;DR

This paper presents an exact solution showing that scalar fields in colliding waves and black holes lead to null singularities, revealing a transition phase between spacelike singularities and regular horizons, with weaker tidal force divergences.

Contribution

It introduces a novel exact solution demonstrating null singularity formation due to scalar fields in colliding waves and black holes, contrasting previous beliefs about spacelike singularities.

Findings

Null singularities occur on null surfaces in scalar field interactions.

Null singularities have weaker tidal force divergences than spacelike ones.

Inner horizons of Reissner-Nordstrom black holes can transform into null singularities with scalar fields.

Abstract

It was believed that when gravitational, electromagnetic and scalar waves interact, a spacelike curvature singularity or Cauchy horizon develops because of mutual focusing. We show with an exact solution that the collision of Einstein-Maxwell-Scalar fields, in contrast to previous studies, predicts singularities on null surfaces and that this is a transition phase between spacelike singularities and regular horizons. Divergences of tidal forces in the null singularities is shown to be weaker relative to the spacelike ones. Using the local isometry between colliding plane waves and black holes, we show that the inner horizon of Reissner-Nordstrom black hole transforms into a null singularity when a particular scalar field is coupled to it. We also present an analytic exact solution, which represents a Reissner-Nordstrom black hole with scalar hair in between the ergosphere.