Effects of an Immortal Stellar Population in AGN Disks
  Stars are likely embedded in the gas disks of Active Galactic Nuclei (AGN).
Theoretical models predict that in the inner regions of the disk these stars
accrete rapidly, with fresh gas replenishing hydrogen in their cores faster
than it is burned into helium, effectively stalling their evolution at hydrogen
burning. We produce order-of-magnitude estimates of the number of such stars in
a fiducial AGN disk. We find numbers of order $10^{2-4}$, confined to the inner
$r_{\rm cap} \sim 3000 r_s \sim 0.03\rm pc$. These stars can profoundly alter
the chemistry of AGN disks, enriching them in helium and depleting them in
hydrogen, both by order-unity amounts. We further consider mergers between
these stars and other disk objects, suggesting that star-star mergers result in
rapid mass loss from the remnant to restore an equilibrium mass, while
star-compact object mergers may result in exotic outcomes and even host binary
black hole mergers within themselves. Finally, we examine how these stars react
as the disk dissipates towards the end of its life, and find that they may
return mass to the disk fast enough to extend its lifetime by a factor of
several and/or may drive powerful outflows from the disk. Post-AGN, these stars
rapidly lose mass and form a population of stellar mass black holes around
$10M_{\odot}$. Due to the complex and uncertain interactions between embedded
stars and the disk, their plausible ubiquity, and their order unity impact on
disk structure and evolution, they must be included in realistic disk models.
