Pulsed Accretion onto Eccentric and Circular Binaries

TL;DR

This study uses advanced numerical simulations to explore how binary star systems with different eccentricities accrete matter, revealing distinct accretion patterns and asymmetries influenced by disk precession.

Contribution

First simulations employing a finite-volume moving-mesh scheme to accurately measure accretion onto individual stars in eccentric and circular binaries.

Findings

Circular binaries show bursty accretion with ~5 P_b period.

Eccentric binaries exhibit accretion modulation at ~1 P_b.

Eccentric binaries can have one star accrete 10-20 times more than the other.

Abstract

We present numerical simulations of circumbinary accretion onto eccentric and circular binaries using the moving-mesh code AREPO. This is the first set of simulations to tackle the problem of binary accretion using a finite-volume scheme on a freely moving mesh, which allows for accurate measurements of accretion onto individual stars for arbitrary binary eccentricity. While accretion onto a circular binary shows bursts with period of ~5 times the binary period P_b,accretion onto an eccentric binary is predominantly modulated at the period ~1P_b. For an equal-mass circular binary, the accretion rates onto individual stars are quite similar to each other, following the same variable pattern in time. By contrast, for eccentric binaries, one of the stars can accrete at a rate 10-20 times larger than its companion. This "symmetry breaking" between the stars, however, alternates over timescales of order 200 P_b, and can be attributed to a slowly precessing, eccentric circumbinary disk. Over longer timescales, the net accretion rates onto individual stars are the same, reaching a quasi-steady state with the circumbinary disk. These results have important implications for the accretion behavior of binary T-Tauri stars and supermassive binary black holes.