The last migration trap of compact objects in AGN accretion disc

ABSTRACT Many black holes detected by the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo detectors are multiple times more massive than those in X-ray binaries. One possibility is that some binary (BBHs) merge within a few Schwarzschild radii of supermassive hole (SMBH), so gravitational waves (GWs) highly redshifted, causing mass inferred from GW signals to appear higher real mass. The difficulty this scenario lies delivery BBH such small distance SMBH. Here we revisit theoretical models for migration compact objects (COs) accretion discs active galactic nuclei (AGNs). We find when rate high disc best described slim model, COs could migrate radius close innermost stable circular orbit be trapped there remaining lifetime AGN. exact trapping coincides with transition region between sub- super-Keplerian rotation disc. call ‘the last trap’ because further inward, can no longer long time. pinpoint parameter space induce trap estimate contributes per cent LIGO/Virgo events. Our result implies couple BBHs discovered far have smaller intrinsic masses.