Spin-induced scalarized black holes

TL;DR

This paper demonstrates that rapidly spinning black holes can develop scalar hair due to a spin-induced instability, confirming the phenomenon of spin-induced scalarization in certain scalar-Gauss-Bonnet theories.

Contribution

It provides the first explicit evidence that Kerr black holes become scalarized when their spin exceeds a critical threshold, leading to new stationary black hole solutions with scalar hair.

Findings

Scalarized black holes exist above a critical spin threshold

Kerr black holes remain unchanged below the threshold

The study supports the phenomenon of spin-induced scalarization

Abstract

It was recently shown that a scalar field suitably coupled to the Gauss-Bonnet invariant $\mathcal{G}$ can undergo a spin-induced linear tachyonic instability near a Kerr black hole. This instability appears only once the dimensionless spin $j$ is sufficiently large, that is, $j \gtrsim 0.5$. A tachyonic instability is the hallmark of spontaneous scalarization. Focusing, for illustrative purposes, on a class of theories that do exhibit this instability, we show that stationary, rotating black hole solutions do indeed have scalar hair once the spin-induced instability threshold is exceeded, while black holes that lie below the threshold are described by the Kerr solution. Our results provide strong support for spin-induced black hole scalarization.