{"work":{"id":"5c2280a4-971a-4dd7-8f47-cea8657e346e","openalex_id":null,"doi":null,"arxiv_id":"2509.23897","raw_key":null,"title":"Aligned hierarchical black hole mergers in active-galactic-nuclei disks revealed by GWTC-4","authors":null,"authors_text":"Y","year":2025,"venue":"astro-ph.HE","abstract":"The active galactic nucleus (AGN) accretion disks are ideal sites for hierarchical black hole (BH) mergers. To robustly probe such a possibility, we analyze binary black hole mergers in the GWTC-4 with a flexible mixture population model for component masses, spin magnitudes, and spin tilt angles, and identify two distinct subpopulations. In the second subpopulation characterized by high spin magnitudes $\\chi\\sim 0.8$ as well as the broad mass distribution up to $\\gtrsim 150M_\\odot$, we find a pronounced preference for spins aligned with the orbital angular momentum: an isotropic tilt distribution is strongly disfavored (logarithmic Bayes factor = 4.5). The aligned events account for $\\sim 0.57^{+0.23}_{-0.31}$ of the second subpopulation, corresponding to a local rate of $\\sim 0.25^{+0.38}_{-0.16} ~ {\\rm Gpc}^{-3} {\\rm yr}^{-1}$ (all values reflect central 90\\% credible intervals). These notable features naturally arise from hierarchical mergers embedded in AGN disks, where gas torques may effectively align spins. Our results suggest that AGN-disk hierarchical assembly may be one important channel for the present gravitational-wave sample, and provide concrete, testable predictions for future detection.","external_url":"https://arxiv.org/abs/2509.23897","cited_by_count":null,"metadata_source":"pith","metadata_fetched_at":"2026-07-03T12:58:07.899236+00:00","pith_arxiv_id":"2509.23897","created_at":"2026-05-08T23:14:22.952675+00:00","updated_at":"2026-07-03T12:58:07.899236+00:00","title_quality_ok":true,"display_title":"Li, Y .-Z","render_title":"Li, Y .-Z"},"hub":{"state":{"work_id":"5c2280a4-971a-4dd7-8f47-cea8657e346e","tier":"hub","tier_reason":"10+ Pith inbound or 1,000+ external citations","pith_inbound_count":16,"external_cited_by_count":null,"distinct_field_count":3,"first_pith_cited_at":"2025-10-26T14:48:06+00:00","last_pith_cited_at":"2026-07-01T16:08:46+00:00","author_build_status":"not_needed","summary_status":"needed","contexts_status":"needed","graph_status":"needed","ask_index_status":"not_needed","reader_status":"not_needed","recognition_status":"not_needed","updated_at":"2026-07-06T08:49:03.538618+00:00","tier_text":"hub"},"tier":"hub","role_counts":[{"context_role":"background","n":4},{"context_role":"method","n":1}],"polarity_counts":[{"context_polarity":"background","n":4},{"context_polarity":"use_method","n":1}],"runs":{},"summary":{},"graph":{},"authors":[]}}