Special TAPIR Seminar

In person: 370 Cahill. To Join via Zoom: 851 0756 7442

ABSTRACT: Simple hydrodynamical models predict that the accretion disks of active galactic nuclei (AGN) become unstable against gravitational instability (GI) at large radii and thus fragment into stars. However, as observations fail to find the expected stellar populations, it has long been assumed that AGN disks stabilize through some undetermined mechanism. Using 3D shearing box simulations, we investigate the ability of MRI to stabilize an AGN accretion disk against GI by driving magnetic pressure dominance within the disk. We find that the magnetic pressure generated by MRI in the magnetically dominated regime is sufficient to stabilize an AGN disk against GI, even if the disk experiences a period of extreme instability against GI. Conversely, we find that gas dominated disks do not stabilize against GI and in the strongly self-gravitating case, fragment as MRI saturates. Further, we find that in disks that do not undergo catastrophic fragmentation, MRI appears to evolve normally, regardless of presence or strength of self-gravity. Finally, we show that the significant metal enrichment of Mrk 573 can be explained by a highly conservative model for in situ, embedded star formation in the outer regions of the accretion disk of Mrk 573's central supermassive black hole. Further, we show that only a thick disk can produce a sufficiently large population of massive stars to explain the observed enrichment, while also showing that only a thick disk could successfully trap the supernova ejecta required to enrich the AGN's outflows. We also show that said disk likely extends to the edge of the SMBH's sphere of influence.