Black hole mergers: can gas discs solve the ‘final parsec’ problem?

By G. Lodato, S. Nayakshin, A. King, J. H. U. D. O. Physics, Astronomy, University of Leicester Dipartimento di Fisica, Universita' di Milano Institute of Astronomy, U. Cambridge. 2009

138 citations recorded by the source corpus.

We compute the effect of an orbiting gas disc in promoting the coalescence of a central supermassive black hole binary. Unlike earlier studies, we consider a finite mass of gas with explicit time dependence: we do not assume that the gas necessarily adopts a steady state or a spatially constant accretion rate, i.e. that the merging black hole was somehow inserted into a pre-existing accretion disc. We consider the tidal torque of the binary on the disc, and the binary's gravitational radiation. We study the effects of star formation in the gas disc in a simple energy feedback framework. The disc spectrum differs in detail from that found before. In particular, tidal torques from the secondary black hole heat the edges of the gap, creating bright rims around the secondary. These rims do not in practice have uniform brightness either in azimuth or time, but can on average account for as much as 50 per cent of the integrated light from the disc. This may lead to detectable high-photon-energy variability on the relatively long orbital time-scale of the secondary black hole, and thus offer a prospective signature of a coalescing black hole binary. We also find that the disc can drive the binary to merger on a reasonable time-scale only if its mass is at least comparable with that of the secondary black hole, and if the initial binary separation is relatively small, i.e. a0≲ 0.05 pc. Star formation complicates the merger further by removing mass from the disc. In the feedback model we consider, this sets an effective limit to the disc mass. As a result, binary merging is unlikely unless the black hole mass ratio is ≲0.001. Gas discs thus appear not to be an effective solution to the ‘last parsec’ problem for a significant class of mergers.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/7096602e13593a6ff8d4af20db0ad9f504e4f567

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Citations in the corpus

Doing Science with eLISA: Astrophysics and Cosmology in the Millihertz Regime (2012, background): “, 1999, MacFadyen and Milosavljević, 2008) if the gas does not fragment in stars (Lodato et al., 2009).”
A LARGE SYSTEMATIC SEARCH FOR CLOSE SUPERMASSIVE BINARY AND RAPIDLY RECOILING BLACK HOLES (2011, unknown): “…of the binary orbit have been explored in an effort to solve this problem, most notably drag by a large gaseous reservoir (e.g. a disk) or torques on a binary at short separations by a circumbinary disk(e.g. Escala et al. 2004; Dotti et al. 2007, 2009b; Cuadra et al. 2009; Lodato et al. 2009).”
Phantom: A Smoothed Particle Hydrodynamics and Magnetohydrodynamics Code for Astrophysics (2017, background): “(92) The initial separation is a0, with τ defined as the time to merger, given by the usual expression (e.g. Lodato et al., 2009) τ ≡ 5 256 a40 µ12(m1 +m2)2 , (93) where µ12 ≡ m1m2 m1 +m2 .”
Tearing up the disc: misaligned accretion on to a binary (2013, background): “This process is too slow to merge the binary in most cases, as any disc with enough mass to affect the binary sufficiently quickly is vulnerable to the gravitational instability, and so forms stars rather than shrinking the binary (Lodato et al. 2009).”
Accretion into the central cavity of a circumbinary disc (2012, background): “In reality, accretion on to the binary could produce significant binary (as well as disc) eccentricity (e.g. Cuadra et al. 2009; Lodato et al. 2009; Roedig et al. 2011).”
Evolution of binary black holes in self gravitating discs. Dissecting the torques (2012, background): “…discs, exploiting a variety of analytical and numerical techniques (Ivanov et al. 1999; Armitage & Natarajan 2002, 2005; Hayasaki et al. 2007, 2008; MacFadyen & Milosavljević 2008; Hayasaki 2009; Cuadra et al. 2009; Lodato et al. 2009; Nixon et al. 2011; Roedig et al. 2011; Shi et al. 2011).”
Limiting eccentricity of subparsec massive black hole binaries surrounded by self-gravitating gas discs (2011, background): “Following this proposal, a number of studies have modelled BH migration in Keplerian, geometrically thin α-discs (Ivanov, Papaloizou & Polnarev 1999; Gould & Rix 2000; Armitage & Natarajan 2002; Haiman, Kocsis & Menou 2009; Lodato et al. 2009).”