Dynamical scalarization in Einstein-Maxwell-dilaton theory

TL;DR

This paper investigates the nonlinear process of scalarization in Einstein-Maxwell-dilaton theory, revealing how charged black holes and naked singularities evolve into stable hairy black holes with complex horizon structures.

Contribution

It provides a detailed analysis of dynamical scalarization starting from charged black holes and naked singularities, highlighting the evolution and final states in asymptotically flat spacetime.

Findings

Dilaton field grows rapidly then oscillates and decays

Hairy black holes from naked singularities develop complex horizon structures

Black hole mass saturates exponentially during scalarization

Abstract

We study the process of fully nonlinear dynamical scalarization starting from a charged black hole or a naked singularity in asymptotically flat spacetime in the Einstein-Maxwell-dilaton theory. Initially the dilaton field is negligible compared to the gravitational and the Maxwell field. Then the dilaton field experiences an immediate growth, later it oscillates with damping amplitude and finally settles down to a finite value. For a hairy black hole develops from an original Reissner-Nordstr\"om black hole, since the dilaton oscillation and decay are almost independent of the coupling parameter, unlike the Anti-de Sitter spacetime it is not easy to distinguish the resulting hairy black hole from the original asymptotically flat charged hole. For a hairy black hole evolves from an original naked singularity, the resulting hairy black hole has rich structures. In the scalarization process, the naked singularity is soon enveloped by one outer horizon, then another horizon is developed and in the end a stable hairy black hole forms and two horizons degenerate into one to protect the singularity. The hairy black hole mass saturates exponentially in the scalarization.