From scalar clouds around evaporating black holes to boson star

Abstract

We study, for the first time, the evolution of a scalar cloud bound to an evaporating black hole. Our simulations of the associated Schrödinger-Poisson system for non-relativistic and spherically symmetric clouds reveal that a scalar cloud may (partially) survive as a self-gravitating boson star if the black hole evaporates adiabatically until its mass becomes less than one half of the cloud's mass. This yields a novel mechanism for boson star formation and shows that, as previously conjectured, bosonic dark matter production by light primordial black holes may result in micro-boson stars with very large occupation numbers, greatly enhancing their potential detectability even for very weakly interacting dark matter particles.

Figures (3)

• Figure 1: Numerical evolution of the (square-root of the) particle number density (blue) for simulation A with $M_{BH,i}/M_c=5$ and $\hat{\tau}=1.5\times 10^5$. Also shown are the stationary solutions for $M_{BH}/M_c=5,2,1$ (dashed gray) and the boson star ground state solution (dashed red).
• Figure 2: Evolution of the energy expectation value for $M_{BH,i}=5M_c$ and $\hat{\tau}=1.5\times 10^5$ (blue), compared with the energy of the boson star solution with the same mass (dashed red).
• Figure 3: Final energy expectation value as a function of the BH-to-cloud mass ratio at the non-adiabatic point.