Disk Accretion Driven by Spiral Shocks

TL;DR

This study numerically investigates how spiral shocks influence angular momentum transport and accretion in astrophysical disks, confirming theoretical predictions and emphasizing the importance of high resolution and time-dependent effects.

Contribution

It provides a validated numerical framework and analytical prescription for understanding shock-driven accretion in disks, extending previous theories to more realistic conditions.

Findings

Good agreement between theory and simulations across various parameters

High resolution is essential for accurately capturing shock effects

Time-dependent pressure support significantly affects mass accretion rates

Abstract

Spiral density waves are known to exist in many astrophysical disks, potentially affecting disk structure and evolution. We conduct a numerical study of the effects produced by a density wave, evolving into a shock, on the characteristics of the underlying disk. We measure the deposition of angular momentum in the disk by spiral shocks of different strength and verify the analytical prediction of Rafikov (2016) for the behavior of this quantity, using shock amplitude (which is potentially observable) as the input variable. Good agreement between the theory and numerics is found as we vary shock amplitude (including highly nonlinear shocks), disk aspect ratio, equation of state, radial profiles of the background density and temperature, and pattern speed of the wave. We show that high numerical resolution is required to properly capture shock-driven transport, especially at low wave amplitudes. We also demonstrate that relating local mass accretion rate to shock dissipation in rapidly evolving disks requires accounting for the time-dependent contribution to the angular momentum budget, caused by the time dependence of the radial pressure support. We provide a simple analytical prescription for the behavior of this contribution and demonstrate its excellent agreement with the simulation results. Using these findings we formulate a theoretical framework for studying one-dimensional (in radius) evolution of the shock-mediated accretion disks, which can be applied to a variety of astrophysical systems.