Circumbinary discs are generally thought to take up angular momentum and energy from the binary orbit over time through gravitational torques mediated by orbital resonances. This process leads to the shrinkage of the binary orbit over time, and is important in a variety of astrophysical contexts including the orbital evolution of stellar binaries, the migration of planets in protoplanetary discs, and the evolution of black hole binaries (stellar and supermassive). The merger of compact object binaries provides a source of gravitational waves in the Universe. Recently, several groups have reported numerical simulations of circumbinary discs that yield the opposite result, finding that the binary expands with time. Here we argue that this result is primarily due to the choice of simulation parameters, made for numerical reasons, which differ from realistic disc parameters in many cases. We provide physical arguments, and then demonstrate with 3D hydrodynamical simulations, that thick (high pressure, high viscosity) discs drive sufficient accretion of high angular momentum material to force binary expansion, while in the more realistic case of thin (low pressure, low viscosity) discs there is less accretion and the binary shrinks. In the latter case, tides, which generally transfer angular momentum and energy from the more rapidly rotating object (the binary) to the less rapidly rotating object (the disc), are the dominant driver of disc-binary evolution. This causes the binary to shrink. We therefore conclude that for common circumbinary disc parameters, binaries with non-extreme mass ratios are expected to shrink over time. Expansion of the binary can occur if the disc viscosity is unusually high, which may occur in the very thick discs encountered in e.g. circumplanetary discs, super-Eddington AGN, or the outer regions of passive protostellar discs that are heated by the ... (abridged).
Supermassive black hole binaries are likely to accrete interstellar gas through a circumbinary disk. Shortly before merger, the inner portions of this circumbinary disk are subject to general relativistic effects. To study this regime, we approximate the spacetime metric of close orbiting black holes by superimposing two boosted Kerr-Schild terms. After demonstrating the quality of this approximation, we carry out very long-term general relativistic magnetohydrodynamic simulations of the circumbinary disk. We consider black holes with spin dimensionless parameters of magnitude 0.9, in one simu…
We review recent works on the dynamics of circumbinary accretion, including time variability, angular momentum transfer between the disk and the binary, and the secular evolution of accreting binaries. These dynamics can impact stellar binary formation/evolution, circumbinary planet formation/migration, and the evolution of (super)massive black-hole binaries. We discuss the dynamics and evolution of inclined/warped circumbinary disks and connect with recent observations of protoplanetary disks. A special kind of circumbinary accretion involves binaries embedded in "big" disks, which may contri…
Tidal disruption events, which occur when a star is shredded by the tidal field of a supermassive black hole, provide a means of fueling black hole accretion. Here we show, using a combination of three body orbit integrations and hydrodynamic simulations, that these events are also capable of generating circumbinary rings of gas around tight supermassive black hole binaries with small mass ratios. Depending on the thermodynamics, these rings can either fragment into clumps that orbit the binary, or evolve into a gaseous circumbinary disc. We argue that tidal disruptions provide a direct means …
Much of the parameter space relevant to the evolution of astrophysical circumbinary accretion discs remains unexplored. We have carried out a suite of circumbinary disc simulations surveying both disc thickness and kinematic viscosity, using both constant-$ν$ and constant-$α$ prescriptions. We focus primarily on disc aspect ratios between $0.1$ and $0.033$, and on viscosities between $ν=0.0005$ and $ν=0.008$ (in units of binary semi-major axis and orbital frequency), and specialise to circular equal-mass binaries. Both factors strongly influence the evolution of the binary semi-major axis: at …
Several black hole low-mass X-ray binaries (BHLMXBs) show very fast orbital shrinkage, which is difficult to understand in the standard picture of the LMXB evolution. Based on the possible detection of a circumbinary (CB) disk in A0620-00 and XTE J1118+480, we investigate the influence of the interaction between a CB disk and the inner binary and calculate the evolution of the binary using the Modules for Experiments in Stellar Astrophysics. We consider two cases for the CB disk formation in which it is fed by mass loss during single outburst or successive outbursts in the LMXB. We show that w…
Massive black hole binaries (MBHBs) represent an unavoidable outcome of hierarchical galaxy formation, but their dynamical evolution at sub-parsec scales is poorly understood, due to a combination of uncertainties in theoretical models and lack of firm observational evidence. In gas rich environments, it has been shown that a putative extended, steady circumbinary gaseous disc plays an important role in the MBHB evolution, facilitating its coalescence. How gas on galactic scales is transported to the nuclear region to form and maintain such a stable structure is, however, unclear. If, followin…
$\textit{BMAD}$-Circumbinary Magnetically Arrested Disks around Stellar or Black Hole Binaries: Hot Accretion Flows, Disk Properties, and Angular Momentum Transfer
We present a suite of high resolution hydrodynamic simulations of binaries immersed in circumbinary accretion disks (CBDs). For the first time, we investigate the preferential accretion rate as a function of both eccentricity $e_{\rm b}$ and mass ratio $q_{\rm b}$ in a densely sampled parameter space, finding that when compared with circular binaries, mass ratios grow more efficiently in binaries on moderately eccentric orbits ($0.0 \lesssim e_{\rm b} \lesssim 0.4$), and high eccentricities ($e_{\rm b} \gtrsim 0.6 $) suppress mass ratio growth. We suggest that this non-monotonic preferential a…
Gaseous circumbinary accretion discs provide a promising mechanism to facilitate the mergers of supermassive black holes (SMBHs) in galactic nuclei. We measure the torques exerted on accreting SMBH binaries, using 2D, isothermal, moving-mesh, viscous hydrodynamical simulations of circumbinary accretion discs. Our computational domain includes the entire inner region of the circumbinary disk with the individual black holes (BHs) included as point masses on the grid and a sink prescription to model accretion onto each BH. The BHs each acquire their own well-resolved accretion discs ("minidiscs")…
We present the results of 2D, moving-mesh, viscous hydrodynamical simulations of an accretion disc around a merging supermassive black hole binary (SMBHB). The simulation is pseudo-Newtonian, with the BHs modeled as point masses with a Paczynski-Wiita potential, and includes viscous heating, shock heating, and radiative cooling. We follow the gravitational inspiral of an equal-mass binary with a component mass M_bh=10^6 M_sun from an initial separation of 60r_g (where r_g=GM_bh/c^2 is the gravitational radius) to the merger. We find that a central, low-density cavity forms around the binary, a…
Recently, the black hole X-ray binary (BHXB) Nova Muscae 1991 has been reported to be experiencing an extremely rapid orbital decay. So far, three BHXBs have anomalously high orbital period derivatives, which can not be interpreted by the standard stellar evolution theory. In this work, we investigate whether the resonant interaction between the binary and a surrounding circumbinary (CB) disk could produce the observed orbital period derivatives. Analytical calculations indicate that the observed orbital period derivatives of XTE J1118+480 and A0620-00 can originate from the tidal torque betwe…
Hydrodynamical interactions between binaries and circumbinary disks (CBDs) play an important role in a variety of astrophysical systems, from young stellar binaries to supermassive black hole binaries. Previous simulations of CBDs have mostly employed locally isothermal equation of state. We carry out two-dimensional viscous hydrodynamic simulations of CBDs around equal-mass, circular binaries, treating the gas thermodynamics by thermal relaxation towards equilibrium temperature (the constant-$β$ cooling ansatz, where $β$ is the cooling time in units of the local Keplerian time). As an initial…
The question whether the interaction of a circumbinary disc with the central binary system leads to shrinking or expansion of the binary orbit has attracted considerable interest as it impacts the evolution of binary black holes and stellar binary stars in their formation phase. We performed two-dimensional hydrodynamical simulations of circumbinary discs for a large parameter set of disc viscosities and thicknesses and two different binary mass ratios for binaries on circular orbits. For those we measured carefully the net angular momentum and mass transfer between disc and binary system, and…
Planetary Desert around Compact Binaries: Dynamical Instability Triggered by Resonance-Induced Eccentricity Excitation
Institute for Astronomy, School of Physics, Zhejiang University（浙江大学物理学院天体物理研究所）；Center for Cosmology and Computational Astrophysics, Institute for Advanced Study in Physics, Zhejiang University（浙江大学物理高等研究院宇宙学与计算天体物理中心）；Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交通大学李政道研究所）；Department of Astronomy, Center for Astrophysics and Planetary Science, Cornell University（康奈尔大学天文学系天文与行星科学中心）
We carry out 2D viscous hydrodynamics simulations of circumbinary disk (CBD) accretion using {\footnotesize AREPO}. We resolve the accretion flow from a large-scale CBD down to the streamers and disks around individual binary components. Extending our recent studies \citep{mun19}, we consider circular binaries with various mass ratios ($0.1\leq q_{\rm{b}}\leq1$) and study accretion from ``infinite'', steady-supply disks and from finite-sized, viscously spreading tori. For ``infinite'' disks, a global steady state can be reached, and the accretion variability has a dominant frequency ${\sim}0.2…
Hydrodynamical simulations show that circumbinary disks become eccentric, even when the binary is circular. Here we demonstrate that, in steady state, the disk's eccentricity behaves as a long-lived free mode trapped by turning points that naturally arise from a continuously truncated density profile. Consequently, both the disk's precession rate and eccentricity profile may be calculated via the simple linear theory for perturbed pressure-supported disks. By formulating and solving the linear theory we find that (i) surprisingly, the precession rate is roughly determined by the binary's quadr…
We carry out 2D viscous hydrodynamical simulations of circumbinary accretion using the AREPO code. We self-consistently compute the accretion flow over a wide range of spatial scales, from the circumbinary disk (CBD) far from the central binary, through accretion streamers, to the disks around individual binary components, resolving the flow down to 2% of the binary separation. We focus on equal-mass binaries with arbitrary eccentricities. We evolve the flow over long (viscous) timescales until a quasi-steady is reached, in which the mass supply rate at large distances $\dot{M}_0$ (assumed con…
Understanding the interaction of massive black hole binaries with their gaseous environment is crucial since at sub-parsec scales the binary is too wide for gravitational wave emission to take over and to drive the two black holes to merge. We here investigate the interaction between a massive black hole binary and a self-gravitating circumbinary disc using 3D smoothed particle hydrodynamics simulations. We find that, when the disc self-gravity regulates the angular momentum transport, the binary semi-major axis decreases regardless the choice of disc masses and temperatures, within the range …
We consider fallback accretion after an ultra-stripped supernova (USSN) that accompanies formation of a binary neutron star (BNS) or a neutron star-black hole binary (NS-BH). The fallback matter initially accretes directly to the nascent NS, while it starts to accrete to the circumbinary disk, typically $0.1\mbox{-}1\, \mathrm{day}$ after the onset of the USSN explosion. The circumbinary disk mass further accretes, forming mini disks around each compact object, with a super-Eddington rate up to a few years. We show that such a system constitutes a binary ultraluminous X-ray source (ULX), and a…
Dynamics and detectability of long-lived non-accretion phases for massive black hole binaries in cold, thermally regulating disks
Niels Bohr International Academy, Niels Bohr Institute（尼尔斯·玻尔国际学院，尼尔斯·玻尔研究所）；Institute of Science and Technology Austria (ISTA)（奥地利科学与技术研究所）；Space Telescope Science Institute（太空望远镜科学研究所）；Johns Hopkins University（约翰斯·霍普金斯大学）
Gaseous disks have been proposed as a mechanism for facilitating mergers of binary black holes. We explore circumbinary disk systems to determine the evolution of the central binary. To do so, we perform 3D, hydrodynamic, locally isothermal simulations of circumbinary disks on a Cartesian grid. We focus on binaries of equal mass ratios on fixed circular orbits. To investigate the orbital evolution of the binary, we examine the various torques exerted on the system. For the case where the disk plane and binary orbital plane are aligned, we find that the total torque is positive so that the semi…
Radiation pressure role in accreting massive black hole binaries
Università degli Studi di Milano-Bicocca（米兰比可卡大学）；INFN, Sezione di Milano-Bicocca（意大利国家核物理研究所米兰比可卡分部）；Università degli Studi di Milano（米兰大学）；DiSAT, Università degli Studi dell’Insubria（因苏布里亚大学 DiSAT）
Relativistic Effects on Circumbinary Orbit Stability
Instituto de Astrofísica de La Plata, CCT La Plata-CONICET-UNLP（拉普拉塔天体物理研究所）；Facultad de Ciencias Astronómicas y Geofísicas de La Plata, UNLP（拉普拉塔大学天文与地球物理学院）；Nevada Center for Astrophysics, University of Nevada, Las Vegas（内华达大学拉斯维加斯分校天体物理中心）；Department of Physics and Astronomy, University of Nevada, Las Vegas（内华达大学拉斯维加斯分校物理与天文学系）
The study of the interaction of a massive black hole binary with its gaseous environment is crucial in order to be able to predict merger rates and possible electromagnetic counterparts of gravitational wave signals. The evolution of the binary semi-major axis resulting from this interaction has been recently debated, and a clear consensus is still missing, also because of several numerical limitations, i.e. fixed orbit binaries or lack of resolution inside the cavity carved by the binary in its circumbinary disc. Using on-the-fly particle-splitting in the 3D meshless code gizmo, we achieve hy…
