| Name: | Parthapratim Mahapatra |
| Affiliation: | Chennai Mathematical Institute |
| Conference ID : | ASI2024_922 |
| Title : | Black hole hierarchical growth efficiency and mass spectrum predictions |
| Authors : | Parthapratim Mahapatra1, Debatri Chattopadhyay2, Anuradha Gupta3, Marc Favata4, B. S. Sathyaprakash256, K. G. Arun15
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| Authors Affiliation: | 1 Chennai Mathematical Institute, Siruseri, 603103, India
2 School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, United Kingdom
3 Department of Physics and Astronomy, The University of Mississippi, Oxford MS 38677, USA
4 Department of Physics & Astronomy, Montclair State University, 1 Normal Avenue, Montclair, NJ 07043, USA
5 Institute for Gravitation and the Cosmos, Department of Physics, Penn State University, University Park, PA 16802, USA
6 Department of Astronomy and Astrophysics, Penn State University, University Park, PA 16802, USA
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| Mode of Presentation: | Oral |
| Abstract Category : | High Energy Phenomena, Fundamental Physics and Astronomy |
| Abstract : | Black holes between 50 to 130 solar masses were thought to be prohibited due to pair-production instabilities in massive stars. Observations of binary black holes with component masses in this range challenge this notion and suggest hierarchical mergers in dense star clusters as the origin of these high masses. When binary black holes (BBHs) merge in dense star clusters, their remnants can pair up with other black holes in the cluster, forming heavier and heavier black holes through the hierarchical merger process. The necessary condition for hierarchical merger to occur is that remnants formed by mergers are retained by the host cluster. Using the publicly available database of gravitational events, we find that high escape speed star clusters (≳ 200 km/s, such as nuclear star clusters) are preferable astrophysical environments to host hierarchical mergers. We construct a simple parametric model for hierarchical mergers in dense star clusters. Our model relies on pairing probability and initial mass functions for the black hole population, along with numerical relativity fitting formulas for the mass, spin, and kick speed of the merger remnant. We assess the efficiency of hierarchical mergers as a function of merger generation and derive the mass distribution of black holes. We find that the multi-modal features in the BBH mass spectrum---unveiled by the non-parametric population models---can be interpreted by invoking the hierarchical merger scenario in dense, metal-rich, stellar environments. |
