Radiation Hydrodynamic Simulations of Massive Stars in Gas-rich Environments: Accretion of AGN Stars Suppressed By Thermal Feedback
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arXiv
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2024
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| author | Chen, Yi-Xian Jiang, Yan-Fei Goodman, Jeremy Lin, Douglas N. C. |
| author_facet | Chen, Yi-Xian Jiang, Yan-Fei Goodman, Jeremy Lin, Douglas N. C. |
| contents | 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 $c/τ$ 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 $c/τ<c_s$, 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 $ρ\gtrsim 10^{-9}$g/cm$^3$, and needs to be treated with caution in 1D long-term calculations. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2408_12017 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Radiation Hydrodynamic Simulations of Massive Stars in Gas-rich Environments: Accretion of AGN Stars Suppressed By Thermal Feedback Chen, Yi-Xian Jiang, Yan-Fei Goodman, Jeremy Lin, Douglas N. C. High Energy Astrophysical Phenomena Astrophysics of Galaxies Solar and Stellar Astrophysics 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 $c/τ$ 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 $c/τ<c_s$, 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 $ρ\gtrsim 10^{-9}$g/cm$^3$, and needs to be treated with caution in 1D long-term calculations. |
| title | Radiation Hydrodynamic Simulations of Massive Stars in Gas-rich Environments: Accretion of AGN Stars Suppressed By Thermal Feedback |
| topic | High Energy Astrophysical Phenomena Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2408.12017 |