Relatore
Descrizione
Stellar clusters are efficient factories of dynamical interactions that shape the black hole (BH) mass distribution observed by gravitational-wave (GW) detectors. Their ability to pair and retain BHs enables the formation of remnants more massive than those produced through isolated binary evolution. This is a crucial difference among binary BH formation channels, as highlighted by events such as GW231123, possibly the first detected merger involving an intermediate-mass black hole (IMBH; mass above 100 solar masses).
We investigate the hierarchical assembly of binary BHs, focusing on the formation and evolution of secondary branches within BH merger trees. We introduce a new formalism implemented in the semi-analytical population-synthesis code BPOP, which tracks the growth of structured hierarchical chains. We define secondary hierarchical mergers as events in which the secondary component is itself a merger remnant, and show that this sub-population, while rare, preferentially populates the high-mass tail of the remnant distribution and contributes significantly to IMBH formation beyond the pair-instability mass gap. Their merger products also carry a distinct spin signature, providing an additional observable handle on their origin.
We show that the multiplicity, and generational depth of secondary merger chains leave characteristic imprints on the remnant mass and spin spectra. Tracking the full hierarchical structure of secondary mergers is essential for correctly interpreting the origin of the most massive BHs observed in GW events.
| Sessione | Onde Gravitazionali e astronomia multimessaggera |
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