{
  "id": "2408.12017",
  "version": "v1",
  "published": "2024-08-21T22:03:12.000Z",
  "updated": "2024-08-21T22:03:12.000Z",
  "title": "Radiation Hydrodynamic Simulations of Massive Stars in Gas-rich Environments: Accretion of AGN Stars Suppressed By Thermal Feedback",
  "authors": [
    "Yi-Xian Chen",
    "Yan-Fei Jiang",
    "Jeremy Goodman",
    "Douglas N. C. Lin"
  ],
  "comment": "Accepted to ApJ, 20 pages, 16 figures",
  "categories": [
    "astro-ph.HE",
    "astro-ph.GA",
    "astro-ph.SR"
  ],
  "abstract": "Massive stars may form in or be captured into AGN disks. Recent 1D studies employing stellar-evolution codes have demonstrated the potential for rapid growth of such stars through accretion up to a few hundred $M_\\odot$. We perform 3D radiation hydrodynamic simulations of moderately massive stars' envelopes, in order to determine the rate and critical radius $R_{\\rm crit}$ of their accretion process in an isotropic gas-rich environment in the absence of luminosity-driven mass loss. We find that in the ``fast-diffusion\" regime where characteristic radiative diffusion speed $c/\\tau$ is faster than the gas sound speed $c_s$, the accretion rate is suppressed by feedback from gravitational and radiative advection energy flux, in addition to the stellar luminosity. Alternatively, in the ``slow-diffusion\" regime where $c/\\tau<c_s$, due to adiabatic accretion, the stellar envelope expands quickly to become hydrostatic and further net accretion occurs on thermal timescales in the absence of self-gravity. When the radiation entropy of the medium is less than that of the star, however, this hydrostatic envelope can become more massive than the star itself. Within this sub-regime, self-gravity of the envelope excites runaway growth. Applying our results to realistic environments, moderately massive stars ($\\lesssim 100M_\\odot$) embedded in AGN disks typically accrete in the fast-diffusion regime, leading to reduction of steady-state accretion rate 1-2 orders of magnitudes lower than expected by previous 1D calculations and $R_{\\rm crit}$ smaller than the disk scale height, except in the opacity window at temperature $T\\sim 2000$K. Accretion in slow diffusion regime occurs in regions with very high density $\\rho\\gtrsim 10^{-9}$g/cm$^3$, and needs to be treated with caution in 1D long-term calculations.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2024-08-21T22:03:12.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "massive stars",
      "gas-rich environment",
      "agn stars",
      "thermal feedback",
      "studies employing stellar-evolution codes"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 20,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}