Journal Club


"Black hole binary formation in AGN discs: from isolation to merger"

Angelos Karakonstantakis (NCAC, Warsaw)

Motivated by the increasing number of detections of merging black holes by LIGO-VIRGO-KAGRA, black hole (BH) binary mergers in the discs of active galactic nuclei (AGNs) is investigated as a possible merger channel. In this pathway, BH encounters in the gas disc form mutually bound BH binary systems through interaction with the gas in the disc and subsequently inspiral through gravitational torques induced by the local gas. To determine the feasibility of this merger pathway, we present the first three-dimensional global hydrodynamic simulations of the formation and evolution of a stellar-mass BH binaries AGN discs with three different AGN disc masses and five different initial radial separations. These 15 simulations show binary capture of prograde and retrograde binaries can be successful in a range of disc densities including cases well below that of a standard radiatively efficient alpha disc, identifying that the majority of these captured binaries are then subsequently hardened by the surrounding gas. The eccentricity evolution depends strongly on the orbital rotation where prograde binaries are governed by gravitational torques form their circumbinary mini disc, with eccentricities being damped, while for retrograde binaries the eccentricities are excited to >~ 0.9 by accretion torques. In two cases, retrograde binaries ultimately undergo a close periapsis passage which results in a merger via gravitational waves after only a few thousand binary orbits. Thus, the merger time-scale can be far shorter than the AGN disc lifetime. These simulations support an efficient AGN disc merger pathway for BHs.

Connar Rowan et al.,  MNRAS (2023)


"Measuring Mass and Radius of the Maximum-mass Nonrotating Neutron Star"

Parikshit Partha Biswas (NCAC, Warsaw)

The mass (𝘔ₜₒᵥ) and radius (𝘙ₜₒᵥ) of the maximum-mass nonrotating neutron star (NS) play a crucial role in constraining the elusive equation of state (EOS) of cold dense matter and in predicting the fate of remnants from binary neutron star (BNS) mergers. In this study, we introduce a novel method to deduce these parameters by examining the mergers of second-generation (2G) BHs with NSs. These 2G BHs are assumed to originate from superamassive neutron stars (SMNSs) formed in BNS mergers. Since the properties of the remnant BHs arising from the collapse of SMNSs follow a universal relation governed by 𝘔ₜₒᵥ and 𝘙ₜₒᵥ, we anticipate that by analyzing a series (∼100 detections) of mass and spin measurements of the 2G BHs using the third-generation ground-based gravitational wave detectors, 𝘔ₜₒᵥ and 𝘙ₜₒᵥ can be determined with a precision of ∼0.01M⊙ and ∼0.6 km, respectively.

Tang, Shao-Peng et al., eprint arXiv:2309.15441 (2023)


"Recent works published by CAMK employees"

Special session (NCAC, Warsaw)

Special session focusing on three recent works published by CAMK employees and students.

  1. Peter Berczik & Marina Ishchenko
    "Milky Way globular clusters on cosmological timescales. III. Interaction rates"
    by Ishchenko et al. 2023
  2. Fatemeh Kayanikhoo
    "Energy distribution and substructure formation in astrophysical MHD simulations"
    by Kayanikhoo et al. 2023
  3. Paulina Sowocka
    "The GW Vir instability strip in the light of new observations of PG 1159 stars. Discovery of pulsations in the central star of Abell 72 and variability of RX J0122.9-7521"
    by Sowocka et al. 2023