Qianhang Ding - Superradiant Bosons Driving Supermassive Black Hole Mergers

Parallel Talk | Cosmology from Home 2025 https://www.cosmologyfromhome.com/ Abstract: Ultralight bosons (ULBs) can form macroscopic superradiant clouds around spinning black holes. We show that for scalar ULB masses μ∼10^(−22)−10^(−21) eV boson cloud dynamical friction drives supermassive black hole (SMBH) final-parsec evolution in ≲1 Gyr and suppresses the nanohertz gravitational wave background with turnover. Considering century-monitored OJ287 system, we place novel bounds restricting ULB mass range μ≃(8.5−22)×10^(−22) eV independent of any dark matter assumptions and show ULB drag can also efficiently reconcile any future confirmations of the debated orbital decay excess. Forthcoming pulsar timing array data and precise SMBH orbital timings will decisively test this scenario.