Gas Accretion from a Circumbinary Disk

TL;DR

This paper introduces a new computational method for studying gas accretion from circumbinary disks, revealing complex accretion dynamics and spiral wave phenomena around binary systems.

Contribution

A novel computational scheme that improves accuracy in simulating gas accretion by decomposing gas velocity and applying it to circumbinary disks with reduced gravity softening.

Findings

Gas accretion varies with time due to spiral arm oscillations.

Primary disk tends to have higher mass accretion rates.

Secondary disk remains relatively stable and quiet.

Abstract

A new computational scheme is developed to study gas accretion from a circumbinary disk. The scheme decomposes the gas velocity into two components one of which denotes the Keplerian rotation and the other of which does the deviation from it. This scheme enables us to solve the centrifugal balance of a gas disk against gravity with better accuracy, since the former inertia force cancels the gravity. It is applied to circumbinary disk rotating around binary of which primary and secondary has mass ratio, 1.4:0.95. The gravity is reduced artificially softened only in small circular regions around the primary and secondary. The radii are 7% of the binary separation and much smaller than those in the previous grid based simulations. 7 Models are constructed to study dependence on the gas temperature and the initial inner radius of the disk. The gas accretion shows both fast and slow time variations while the binary is assumed to have a circular orbit. The time variation is due to oscillation of spiral arms in the circumbinary disk. The masses of primary and secondary disks increase while oscillating appreciably. The mass accretion rate tends to be higher for the primary disk although the secondary disk has a higher accretion rate in certain periods. The primary disk is perturbed intensely by the impact of gas flow so that the outer part is removed. The secondary disk is quiet in most of time on the contrary. Both the primary and secondary disks have traveling spiral waves which transfer angular momentum within them.