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SUMMARY:Double black hole mergers in nuclear star clusters: eccentricities
 \, spins\, masses\, and the growth of massive seeds - Debatri Chattopadhya
 y
DTSTART:20250709T121500Z
DTEND:20250709T124500Z
UID:TALK234226@talks.cam.ac.uk
CONTACT:Cristiano Longarini
DESCRIPTION:We investigate the formation of intermediate-mass black holes 
 (IMBHs) through hierarchical mergers of stellar-origin black holes (BHs)\,
  as well as BH mergers formed dynamically in nuclear star clusters. Using 
 a semi-analytical approach that incorporates probabilistic\, mass-function
 –dependent double-BH (DBH) pairing\, binary–single encounters\, and a 
 mass-ratio–dependent prescription for energy dissipation in hardening bi
 naries\, we find that IMBHs with masses of order 10²–10⁴ M⊙ can be 
 formed solely through hierarchical mergers on timescales of a few hundred 
 Myr to a few Gyr. Clusters with escape velocities ≳ 400 km s⁻¹ inevit
 ably form high-mass IMBHs. The spin distribution of IMBHs with masses ≳ 
 10³ M⊙ is strongly clustered at χ ≈ 0.15\, while for lower masses it
  peaks at χ ≈ 0.7. Eccentric mergers are more frequent for equal-mass b
 inaries containing first- and second-generation BHs. Metal-rich\, young\, 
 dense clusters can produce up to 20 % of their DBH mergers with eccentrici
 ty ≥ 0.1 at 10 Hz\, and ~ 2–9 % of all in-cluster mergers form at > 10
  Hz. Nuclear star clusters are therefore promising environments for the fo
 rmation of highly eccentric DBH mergers\, detectable with current gravitat
 ional-wave detectors. Clusters of extreme mass (∼ 10⁸ M⊙) and densit
 y (∼ 10⁸ M⊙ pc⁻³) can have about half of their DBH mergers with p
 rimary masses ≥ 100 M⊙. The fraction of in-cluster mergers increases r
 apidly with increasing escape velocity\, approaching unity for Vesc ≳ 20
 0 km s⁻¹. The cosmological DBH merger rate from nuclear clusters varies
  from ≲ 0.01 to 1 Gpc⁻³ yr⁻¹\, where the large uncertainties stem 
 from cluster initial conditions\, number-density distributions\, and the r
 edshift evolution of nucleated galaxies.\n 
LOCATION:Hoyle Lecture theatre + Zoom 
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