Accretion into the Central Cavity of a Circumbinary Disk

Daniel J. D'Orazio; Zoltán Haiman; Andrew MacFadyen

doi:10.1093/mnras/stt1787

paper

Accretion into the Central Cavity of a Circumbinary Disk

arXiv:1210.0536 · doi:10.1093/mnras/stt1787

Abstract

A near-equal mass binary black hole can clear a central cavity in a circumbinary accretion disk; however, previous works have revealed accretion streams entering this cavity. Here we use 2D hydrodynamical simulations to study the accretion streams and their periodic behavior. In particular, we perform a suite of simulations, covering different binary mass ratios $q = M_{2} / M_{1}$ in the range $0.01 \leq q \leq 1$ . In each case, we follow the system for several thousand binary orbits, until it relaxes to a stable accretion pattern. We find the following results: (i) while the binary is efficient in maintaining a low-density cavity, the time-averaged mass accretion rate into the cavity, through narrow coherent accretion streams, is suppressed by at most a factor of $\sim 5$ , compared to a disk with a single BH with the same mass; (ii) the largest suppression occurs for $q \approx 0.05$ ; binaries whose mass ratios are either lower or higher both suppress accretion less significantly; (iii) for $q ≳ 0.05$ , the accretion rate is strongly modulated by the binary, and depending on the precise value of $q$ , the power spectrum of the accretion rate shows either one, two, or three distinct periods; and (v) for $q ≲ 0.05$ , the accretion rate becomes steady, with no time-variations. Most binaries produced in galactic mergers are expected to have $q ≳ 0.05$ . If the luminosity of these binaries tracks their accretion rate, then a periodogram of their light-curve could help in their identification, and to constrain their mass ratio and disk properties.

Published in MNRAS

Accretion into the Central Cavity of a Circumbinary Disk

Abstract

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