Merging timescale for the supermassive black hole binary in interacting galaxy NGC 6240

Abstract

Context. One of the mechanisms leading to the creation of a supermassive black hole (SMBH) is the so-called hierarchical merging scenario. Central SMBHs at the final phase of interacting and coalescing host-galaxies are observed as SMBH binary (SMBHB) candidates at different separations from hundreds of parsecs to megaparsecs. Aims. Today one of the strongest SMBHB candidates is the ultraluminous infrared galaxy NGC 6240 which was spatially and spectroscopically resolved in X-rays by Chandra. Dynamical calculation of central SMBHBs merging in a dense stellar environment allows us to retrace their evolution from kiloparsec to megaparsec scales. The main goal of our dynamical modeling was to reach the final, gravitational wave emission regime for the model BHs. Methods. We present direct N-body simulations with up to one million particles and relativistic post-Newtonian corrections for the SMBH particles up to 3.5 post-Newtonian terms. Results. Generally speaking, the set of initial physical conditions can strongly affect our merging time estimations. However, within a certain range of our parameters, we do not find any strong correlation between merging time and BH-to-BH mass or BH-to-bulge mass ratios. Varying the numerical parameters (like particle number – N) does not significantly change the merging time limits. From our 20 models, we find an upper limit on the merging time for central SMBHBs of less than ∼55 Myr. This precise number is only valid for our combination of initial mass ratios. Conclusions. Further detailed research of rare dual and multiple BHs in dense stellar environments (based on observational data) could clarify the dynamical co-evolution of central BHs and their host-galaxies.

Stellar and black hole assembly inz< 0.3 infrared-luminous mergers: intermittent starbursts versus super-Eddington accretion

“…Conversely, post super-Eddington systems will have a single nucleus and < 1. Additionally, simulations suggest that an SMBH-SMBH merger can take place on the required timescale (Sobolenko et al 2021) so we assume that it does and that it contributes a 25% mass increase at the end of the super-Eddington phase (allowing for unequal mass mergers). The mass at the end of the super-Eddington phase is then: M BH (after) = (9.75 ± 2.22) × 10 7 M (10)…”

Signatures of supermassive black hole binaries on maser systems

“…The JWST data thus provides evidence for depletion of SMBHB or a greater proportion of gas-rich mergers -which are believed to be responsible for AGN activity -attenuating the PTA signal due to the rapid shrinking of their orbits (Kocsis & Sesana 2011;Haiman et al 2009;Armitage & Natarajan 2005). Deviations from circular orbits, as assumed throughout the present calculations, may also arise from wet mergers (e.g., Sobolenko et al 2021). Future PTA data, in combination with larger samples of dual and binary AGN expected with e.g., X-ray facilities (Foord et al 2023), will help narrow down the possibilities and improve our understanding of black hole evolution and feedback mechanisms.…”

Stellar and black hole assembly in z<0.3 infrared-luminous mergers: intermittent starbursts vs. super-Eddington accretion

“…Conversely, post super-Eddington systems will have a single nucleus and 𝜆 𝑒 < 1. Additionally, simulations suggest that an SMBH-SMBH merger can take place on the required timescale (Sobolenko et al 2021) so we assume that it does and that it contributes a 25% mass increase at the end of the super-Eddington phase (allowing for unequal mass mergers). The mass at the end of the super-Eddington phase is then:…”