Accretion into the central cavity of a circumbinary disc

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

    Research output: Contribution to journalArticle

    Abstract

    A near-equal-mass binary black hole (BH) can clear a central cavity in a circumbinary accretion disc; however, previousworks have revealed accretion streams entering this cavity.Herewe use 2D hydrodynamical simulations to study the accretion streams and their periodic behaviour. In particular, we perform a suite of simulations, covering different binary mass ratios q =M2/M1 in the range 0.003 ≤ q ≤ 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) the binary is efficient in maintaining a low-density cavity. However, the time-averaged mass accretion rate into the cavity, through narrow coherent accretion streams, is suppressed by at most a factor of a few compared to a disc with a single BH with the same mass; (ii) 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 (iii) 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 disc properties.

    Original languageEnglish (US)
    Article numberstt1787
    Pages (from-to)2997-3020
    Number of pages24
    JournalMonthly Notices of the Royal Astronomical Society
    Volume436
    Issue number4
    DOIs
    StatePublished - Dec 1 2013

    Keywords

    • Accretion
    • Accretion discs
    • Active
    • Black hole physics
    • Galaxies
    • Gravitational waves

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

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