Three Dimensional MHD Simulation of Circumbinary Accretion Disks -2. Net Accretion Rate

TL;DR

This paper uses 3D MHD simulations to show that the net accretion rate onto binaries is not significantly reduced by binary torques, contrasting earlier analytic predictions.

Contribution

The study demonstrates through 3D MHD simulations that the accretion rate onto binaries remains high, resolving discrepancies with previous analytic models.

Findings

Accretion rates are similar at large radii and onto the binary.

A small subset of gas trajectories dominate accretion.

Discrepancies with earlier analytic estimates are explained.

Abstract

When an accretion disk surrounds a binary rotating in the same sense, the binary exerts strong torques on the gas. Analytic work in the 1D approximation indicated that these torques sharply diminish or even eliminate accretion from the disk onto the binary. However, recent 2D and 3D simulational work has shown at most modest diminution. We present new MHD simulations demonstrating that for binaries with mass ratios of 1 and 0.1 there is essentially no difference between the accretion rate at large radius in the disk and the accretion rate onto the binary. To resolve the discrepancy with earlier analytic estimates, we identify the small subset of gas trajectories traveling from the inner edge of the disk to the binary and show how the full accretion rate is concentrated onto them.