The nature of tilted supercritical accretion discs

TL;DR

This study presents the first 3D general relativistic radiation magnetohydrodynamic simulations of tilted supercritical accretion discs, revealing tilt-dependent enhancements in accretion rates and the role of standing shocks.

Contribution

It demonstrates that tilt can significantly increase accretion rates and introduces the impact of standing shocks in tilted discs, advancing understanding of black hole growth.

Findings

Tilted discs can have accretion rates up to ten times higher than untilted ones.

Accretion rate enhancement scales linearly with tilt angle and black hole spin.

Tilted discs are more advective due to standing shocks in the inner regions.

Abstract

In this paper, we report on the first 3D general relativistic radiation magnetohydrodynamic simulations of large supercritical accretion discs that are tilted with respect to the black hole spin axis. We explore a range of black hole spin parameters (from $a_* = -0.9$ to 0.9), initial tilts (in the range from $\beta_0 = 0^\circ$ to $30^\circ$), and target mass accretion rates. We first confirm that, for all the untilted simulations, the Eddington accretion limit is obeyed ($\dot{M}_\mathrm{BH} \lesssim \dot{M}_\mathrm{Edd}$), consistent with our previous findings. However, for tilted discs we find that the mass accretion rate can be enhanced by up to a factor of ten and that factor depends linearly on tilt $\dot{M}_\mathrm{BH} \propto \beta_0 \ge \dot{M}_\mathrm{Edd}$. This could be an important aspect in solving the puzzle of the growth of the first supermassive black holes. We also find that for a given tilt, the mass accretion rate enhancement is proportional to the magnitude of the spin. Additionally, we find that tilted supercritical accretion discs are more advective than their untilted counterparts. We attribute all of these differences to the presence of standing shocks in the inner regions of the accretion flow, a feature unique to tilted discs.