The formation of mini-AGN discs around IMBHs and their dynamical implications

This study explores the formation and implications of mini-active galactic nucleus (mAGN) discs around intermediate-mass black holes (IMBHs) embedded in gas-rich globular/nuclear clusters (GCs). We examine the parameter space for stable mAGN discs, considering the influence of IMBH mass, disc radius, and gas density on disc stability. The dynamics of stars and black holes within the mAGN disc are modelled, with a focus on gas-induced migration and gas dynamical friction. These dynamical processes can lead to several potentially observable phenomena, including the enhancement of gravitational wave mergers (particularly intermediate-mass ratio inspirals and extreme-mass ratio inspirals), and the occurrence of milli/centi-tidal disruption events with unique observational signatures. We find that gas hardening can significantly accelerate the inspiral of binaries within the disc, potentially leading to a frequency shift in the emitted gravitational waves. Additionally, we explore the possibility of forming accreting IMBH systems from captured binaries within the mAGN disc, potentially resulting in the formation of ultraluminous X-ray sources. The observational implications of such accreting systems, including X-ray emission, optical signatures, and transient phenomena, are discussed. Furthermore, we investigate the possibility of large-scale jets emanating from gas-embedded IMBHs in GCs. While several caveats and uncertainties exist, our work highlights the potential for mAGN discs to provide unique insights into IMBH demographics, accretion physics, and the dynamics of GCs.