AI 中文总结
该研究通过三维流体动力学模拟，探究AGN盘内恒星吸积的绝热 regime，发现高热质量比下会触发包层强激波，近自引力盘内满足条件时会发生自引力诱导的失控坍缩，可形成~10⁵M_⊙的超大质量恒星。
AI 中文摘要
嵌入在超大质量黑洞（SMBH）周围活动星系核（AGN）吸积盘中的大质量恒星的吸积，在快扩散或辐射效率极限下（c/τ > cₛ，其中τ为吸积流的光学深度，cₛ为声速）被限制在恒星爱丁顿率。然而，当环境密度足够高时，适用相反的慢扩散极限。在该极限下，吸积准绝热地进行，并形成流体静力学的星周包层（CSE），在无自引力时会阻止进一步的质量流入。我们在绝热极限下进行三维流体动力学模拟，以研究此类包层的结构与演化。对于低热质量比q_th ≡ M_⋆/M_th（其中M_th = cₛ³/(GΩ)为热质量），CSE边界与环境吸积盘的熵和密度平滑匹配，不会形成激波。相反，当q_th ≫ 1时，包层边界会形成强激波，大幅增加包层的熵，从而限制其结构与质量M_env。在Toomre参数Q ~ 1的近自引力吸积盘中，我们发现当q_th足够大时，包层质量满足M_env/M_⋆ ≳ 1。该条件等价于：进入包层的激后物质的辐射熵低于特征恒星值，当我们的模拟中包含包层自引力时，会在动力学时标上触发动力学失控增长。在具有~10⁸M_⊙ SMBH的真实AGN吸积盘环境中，失控增长可能发生在接近最小自引力半径处，并产生~10⁵M_⊙的超大质量恒星。
英文摘要
Accretion onto massive stars embedded in Active Galactic Nuclei (AGN) disks around supermassive black holes (SMBHs) is regulated to the stellar Eddington rate in the fast-diffusion or radiatively-efficient limit, $c/τ> c_s$, where $τ$ is the optical depth of the accretion flow and $c_s$ the sound speed. However, when the ambient density is sufficiently high, the opposite slow-diffusion limit applies. In this regime, accretion proceeds quasi-adiabatically and forms a hydrostatic circumstellar envelope (CSE) that stalls further mass inflow in the absence of self-gravity. We perform 3D hydrodynamic simulations in the adiabatic limit to investigate the structure and evolution of such envelopes. For low thermal mass ratios, $q_{\rm th} \equiv M_\star/M_{\rm th}$ where $M_{\rm th}=c_s^3/(GΩ)$ is the thermal mass, the CSE boundary smoothly matches the ambient disk entropy and density without forming a shock. In contrast, when $q_{\rm th} \gg 1$, a strong shock develops at the envelope boundary, substantially increasing the entropy of the envelope and thereby regulating its structure and mass, $M_{\rm env}$. In marginally self-gravitating disks with Toomre parameter $Q \sim 1$, we find that at sufficiently large $q_{\rm th}$ the envelope mass satisfies $M_{\rm env}/M_\star \gtrsim 1$. This condition is equivalent to stating that the post-shock material entering the envelope possesses lower radiation entropy than the characteristic stellar value, which triggers dynamical runaway growth on a dynamical timescale once envelope self-gravity is included in our simulations. In realistic AGN disk environments with SMBH mass $\sim 10^8M_\odot$, runaway may occur close to the minimum self-gravitating radii and produce supermassive stars of $\sim 10^5M_\odot$.
CommentsAccepted to ApJ
