最大吸积超大质量恒星：流体静力平衡的基本限制
Maximally accreting supermassive stars: a fundamental limit imposed by hydrostatic equilibrium
摘要：
富含气体的星系的大合并提供了通过直接坍缩形成超大质量黑洞（SMBHs; $\gtrsim10^5$ M $_\odot$）的有利条件，因为它们可以在亚秒差距尺度上触发高达$10^4-10^5$ M $_\odot$ yr $^{-1}$的质量流入。然而，在这种情况下，SMBH形成的通道，无论是暗坍缩（直接坍缩没有事先恒星阶段）或超大质量恒星（SMS; $\gtrsim10^4$ M $_\odot$），仍然未知。在这里，我们调查吸积率的限制，恒星可以保持流体静力平衡。我们计算流体静力学模型的SMSs吸积在$1-1000$ M $_\odot$ yr $^{-1}$，并估计偏离平衡的后验考虑到有限的声速。我们发现吸积超过原子冷却极限（$\gtrsim10$ M $_\odot$ yr $^{-1}$）的恒星只有在超大质量时才能维持流体静力平衡。在这种情况下，它们以一种向液性结构演化，也就是说，熵是局部守恒的，并且与质量坐标的平方根成比例。我们的结果意味着恒星只有在原子冷却晕的速率下（$\sim0.1-10$ M $_\odot$ yr $^{-1}$）通过吸积才能变成超大质量。一旦它们是超大质量的，更大的速率是可能的。
英文摘要：
Major mergers of gas-rich galaxies provide promising conditions for the formation of supermassive black holes (SMBHs; $\gtrsim10^5$ M$_\odot$) by direct collapse because they can trigger mass inflows as high as $10^4-10^5$ M$_\odot$ yr$^{-1}$ on sub-parsec scales. However, the channel of SMBH formation in this case, either dark collapse (direct collapse without prior stellar phase) or supermassive star (SMS; $\gtrsim10^4$ M$_\odot$), remains unknown. Here, we investigate the limit in accretion rate up to which stars can maintain hydrostatic equilibrium. We compute hydrostatic models of SMSs accreting at $1-1000$ M$_\odot$ yr$^{-1}$, and estimate the departures from equilibrium a posteriori by taking into account the finite speed of sound. We find that stars accreting above the atomic cooling limit ($\gtrsim10$ M$_\odot$ yr$^{-1}$) can only maintain hydrostatic equilibrium once they are supermassive. In this case, they evolve adiabatically with a hylotropic structure, that is, entropy is locally conserved and scales with the square root of the mass coordinate. Our results imply that stars can only become supermassive by accretion at the rates of atomically cooled haloes ($\sim0.1-10$ M$_\odot$ yr$^{-1}$). Once they are supermassive, larger rates are possible.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
