Effects of an Immortal Stellar Population in AGN Disks

Abstract

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 $r_{\mathrm{cap}}\sim 3000r_s\sim 0.03\mathrm{pc}$. 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.

12 pages, 2 figures. Accepted in ApJ

References in corpus (15)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• The Zwicky Transient Facility: Science Objectives
• The Two Young Star Disks in the Central Parsec of the Galaxy: Properties, Dynamics and Formation
• Candidate Electromagnetic Counterpart to the Binary Black Hole Merger Gravitational Wave Event S190521g
• Intermediate mass black holes in AGN disks II. Model predictions & observational constraints
• On the rate of black hole binary mergers in galactic nuclei due to dynamical hardening
• Quasistars: Accreting black holes inside massive envelopes
• Understanding extreme quasar optical variability with CRTS: I. Major AGN flares
• Star Formation in Accretion Disks and SMBH Growth
• Electromagnetic Signatures of Relativistic Explosions in AGN Disks
• Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Gravitational Wave Bursts and Electromagnetic Counterparts from Merging Stellar Black Hole Binaries
• The large-scale ionization cones in the Galaxy
• Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Slowly Transient Appearance
• Numerical simulations of continuum-driven winds of super-Eddington stars
• Symmetry Breaking in Dynamical Encounters in the Disks of Active Galactic Nuclei

Cited by in corpus (8)

• In-situ extreme mass ratio inspirals via sub-parsec formation and migration of stars in thin, gravitationally unstable AGN discs
• Capture of stars into gaseous discs around massive black holes: Alignment, circularization and growth
• Starfall: A heavy rain of stars in 'turning on' AGN
• Aligning Retrograde Nuclear Cluster Orbits with an Active Galactic Nucleus Accretion Disc
• Investigating the Nature of the Luminous Ambiguous Nuclear Transient ASASSN-17jz
• In-situ star formation in accretion disk and explanation for correlation between black hole mass and metallicity in AGNs
• Constraints on the Galactic Centre environment from Gaia hypervelocity stars II: The evolved population
• The Influence of Disk Composition on the Evolution of Stars in the Disks of Active Galactic Nuclei