Self-interacting dark scalar spikes around black holes via relativistic Bondi accretion

We consider the spike mass density profile in a dark halo by self-consistently solving the relativistic Bondi accretion of dark matter onto a non-spining black hole of mass M. We assume that the dominant component of the dark matter in the halo is a Standard model gauge-singlet scalar. Its mass m similar or equal to 10(-5) eV and quartic self-coupling less than or similar to 10(-19) are constrained to be compatible with the properties of galactic dark halos. In the hydrodynamic limit, we find that the accretion rate is bounded from below, (M)over dot(min )= 96 pi G(2) M-2 m(4) /lambda(h) over bar (3). Therefore, for M = 10(6) M(circle dot )we have (M)over dot(min) similar or equal to 1.41 x 10(-9) M-circle dot yr(-1), which is subdominant compared to the Eddington accretion of baryons. The spike density profile rho(0)(r) within the self-gravitating regime cannot be fitted well by a single-power law but a double-power one. Despite that, we can fit rho(0)(r) piecewise and find that rho(0)(r) proportional to r(-1.20) near the sound horizon, rho(0)(r) proportional to r(-1.00) towards the Bondi radius and rho(0)(r) proportional to r(-1.)(08) for the region in between. This contrasts with more cuspy rho(0)(r) proportional to r(-1.75) for dark matter with Coulomb-like self-interaction.

Automated summary

In this study, the spike mass density profile in a dark halo is considered by self-consistently solving the relativistic Bondi accretion of dark matter onto a non-spining black hole. It is found that the spike density profile cannot be well fitted by a single-power law, but a double-power one.