Search

Theoretical predictions suggest that very massive stars have the potential to form through multiple collisions and eventually evolve into intermediate-mass black holes (IMBHs) within Population III star clusters embedded in mini dark matter haloes. In this study, we investigate the long-term evolution of Population III star clusters, including models with a primordial binary fraction of |$f_{\rm b}=0$| and 1, using the N -body simulation code petar. We comprehensively examine the phenomenon of hierarchical triple black holes in the clusters, specifically focusing on their merging inner binary black holes (BBHs), with post-Newtonian correction, by using the tsunami code. Our findings suggest a high likelihood of the inner BBHs containing IMBHs with masses on the order of |$\mathcal {O}(100)\,{\rm M}_{\odot }$|⁠ , and as a result, their merger rate could be up to |$0.1{\rm Gpc}^{-3}{\rm yr}^{-3}$|⁠. The orbital eccentricities of some merging inner BBHs oscillate over time periodically, known as the Kozai–Lidov oscillation, due to dynamical perturbations. Detectable merging inner BBHs for mHz GW detectors LISA/TianQin/Taiji concentrate within |$z\lt 3$|⁠. More distant sources would be detectable for CE/ET/LIGO/KAGRA/DECIGO, which are sensitive from |$\mathcal {O}(0.1)$| Hz to |$\mathcal {O}(100)$| Hz. Furthermore, compared with merging isolated BBHs, merging inner BBHs affected by dynamical perturbations from tertiary BHs tend to have higher eccentricities, with a significant fraction of sources with eccentricities closing to 1 at mHz bands. GW observations would help constrain the formation channels of merging BBHs, whether through isolated evolution or dynamical interaction, by examining eccentricities. [ABSTRACT FROM AUTHOR]

Recently discovered regular X-ray bursts known as quasi-periodic eruptions have a proposed model that suggests a tidal stripping white dwarf inspiralling into the galaxy's central black hole on an eccentric orbit. According to this model, the interaction of the stripping white dwarf with the central black hole would also emit gravitational wave signals, their detection can help explore the formation mechanism of quasi-periodic eruptions and facilitate multimessenger observations. In this paper, we investigated the horizon distance of TianQin on this type of gravitation wave signal and found it can be set to 200 Mpc. We also find that those stripping white dwarf model sources with central black hole mass within |$10^4 \!-\! 10^{5.5}\, \mathrm{M}_\odot$| are more likely to be detected by TianQin. We assessed the parameter estimation precision of TianQin on those stripping white dwarf model sources. Our result shows that, even in the worst case, TianQin can determine the central black hole mass, the white dwarf mass, the central black hole spin, and the orbital initial eccentricity with a precision of 10−2. In the optimistic case, TianQin can determine the central black hole mass and the white dwarf mass with a precision of 10−7, determine the central black hole spin with a precision of 10−5, and determine the orbital initial eccentricity with a precision of 10−8. Moreover, TianQin can determine the luminosity distance with a precision of 10−1 and determine the sky localization with a precision of 10−2–10  |$\rm deg^2$|⁠. [ABSTRACT FROM AUTHOR]