Evolution of binary black holes in self gravitating discs. Dissecting the torques

By C. Roedig, A. Sesana, M. Dotti, J. Cuadra, P. Amaro-Seoane, F. Haardt. 2012

133 citations recorded by the source corpus.

Context. Massive black hole binaries, formed in galaxy mergers, are expected to evolve in dense circumbinary discs. Understanding of the disc-binary coupled dynamics is vital to assess both t he final fate of the system and the potential observable featu res that may be tested against observations. Aims. Aimed at understanding the physical roots of the secular evolution of the binary, we study the interplay between gas accretion and gravity torques in changing the binary elements (semi-major axis and eccentricity) and its total angular momentum budget. We pay special attention to the gravity torques, by analysing t heir physical origin and location within the disc. Methods. We analyse three-dimensional smoothed particle hydrodynamics simulations of the evolution of initially quasi-circu lar massive black hole binaries (BHBs) residing in the central hollow (cavity) of massive self-gravitating circumbinary discs. We perfo rm a set of simulations adopting different thermodynamics for the gas within the cavity and for the ’numerical size’ of the black holes. Results. We show that (i) the BHB eccentricity growth found in our previous work is a general result, independent of the accretion a nd the adopted thermodynamics; (ii) the semi-major axis decay depends not only on the gravity torques but also on their subt le interplay with the disc-binary angular momentum transfer due to accretion; (iii) the spectral structure of the gravity torques is predominately caused by disc edge overdensities and spiral arms developing in the body of the disc and, in general, does not reflect direc tly the period of the binary; (iv) the net gravity torque changes sig n across the BHB corotation radius (positive inside vs negative outside) We quantify the relative importance of the two, which appear to depend on the thermodynamical properties of the instreaming gas, and which is crucial in assessing the disc‐binary angular momentum transfer; (v) the net torque manifests as a purely kin ematic (non-resonant) effect as it stems from the low density cavity, where the material flows in and out in highly eccentric orbits. Conclusions. Both accretion onto the black holes and the interaction with gas streams inside the cavity must be taken into account to assess the fate of the binary. Moreover, the total torque exe rted by the disc affects the binary angular momentum by changing all the elements (mass, mass ratio, eccentricity, semimajor axis) of the black hole pair. Commonly used prescriptions equating tidal torque to semi-major axis shrinking might therefore be poor approximations for real astrophysical systems.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/8978f8670eb26003f0e30018b2a733a8fdcbb195

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Citations in the corpus

The quest for dual and binary supermassive black holes: A multi-messenger view (2019, methodology): “Additionally, the mass accretion rate onto the SMBHs is modulated periodically (Hayasaki et al., 2007b; MacFadyen and Milosavljević, 2008; Roedig et al., 2012; D’Orazio et al., 2013; Farris et al., 2014; Shi and Krolik, 2015), which may be translated into periodic modulation of the brightness of the”
Accretion into the central cavity of a circumbinary disc (2012, methodology): “Similar overdense lumps have also been found and described in the 3D MHD simulations of Shi et al. (2012); more recently, Roedig et al. (2011, 2012) have also mentioned the contributions of such lumps to fluctuations in the accretion rate.”
BINARY BLACK HOLE ACCRETION FROM A CIRCUMBINARY DISK: GAS DYNAMICS INSIDE THE CENTRAL CAVITY (2013, methodology): “Similar results have been found previously in SPH calculations (Hayasaki et al. 2007; Cuadra et al. 2009; Roedig et al. 2011, 2012).”
The NANOGrav 11-year Data Set: High-precision Timing of 45 Millisecond Pulsars (2017, background): “Its detection is likely within a few years (Taylor et al. 2016), depending on the underlying astrophysics of supermassive black hole binary mergers (Kocsis & Sesana 2011; Roedig et al. 2012; Sampson et al. 2015; Arzoumanian et al. 2016; Taylor et al. 2017).”
A Population of Short-Period Variable Quasars from PTF as Supermassive Black Hole Binary Candidates (2016, background): “Hydrodynamical simulations of SMBHBs with higher mass ratios (q > 0.3) predict the existence of several periodic components in the variability (Roedig et al. 2012; Shi et al. 2012; D’Orazio, Haiman & MacFadyen 2013; Farris et al. 2014).”
Rapid and Bright Stellar-mass Binary Black Hole Mergers in Active Galactic Nuclei (2016, background): “In this case, the background AGN disk can again be ignored, and the orbital decay of the BBH arises from the torques due to the density perturbations it creates in the minidisk (Goldreich & Tremaine 1980; Cuadra et al. 2009; Roedig et al. 2012; D’Orazio et al. 2013).”
Unveiling the gravitational universe at μ-Hz frequencies (2019, background): “the shape of the gas distribution near the edges of the minidiscs ahead of and behind the MBHs [217], which are hard to resolve properly.”