Spin-Induced Scalarized Black Holes

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