恒星级食客：恒星合并如何驱动极端大质量恒星的物质流失
Massive stellar cannibals: How stellar mergers drive mass-loss in extremely massive stars
AI总结：
本研究通过模拟恒星合并过程，揭示了极端大质量恒星中由合并引起的物质流失机制及其对宇宙化学演化的影响。
摘要：
有理论认为，形成极端大质量和超大质量恒星（>10^3 M_太阳）可能是低金属licity（Z<10^-1 Z_太阳）和密集（≥10^3 M_太阳 pc^-3）恒星环境中的恒星合并的结果。这些天体仍然相关，因为它们可以作为中等质量黑洞的前身，并且是显著的化学污染候选者，这从宇宙历史中观察到的奇特丰度中得到证明。本研究在流体动力学框架内探讨了极端大质量恒星中由合并引起的物质流失，并提供了从模拟中得出的处方，以估算系统的物质流失和相互作用的结果。我们采用了1D的流体动力学、恒星结构和演化学代码MESA来模拟恒星吸积。在我们的模拟中，我们考虑了质量大于1000 M_太阳的恒星，其吸积伴星质量小于100 M_太阳；因此，质量比小于0.1。随着吸积的进行，系统的轨道能量通过流体动力学和引力阻尼力损失。这部分能量被沉积在极端大质量恒星的包层中。我们发现总抛射质量约为系统质量的10-30%。我们的结果指出，大部分由吸积沉积的能量被用来抛射物质。这些发现表明，对于所考虑的配置，由合并引起的物质流失是不可忽视的。因此，当研究极端大质量恒星的形成并预测其在宇宙历史中的可能作用时，这是一个重要的过程。
英文摘要：
It has been theorized that the formation of extremely massive and supermassive stars ($>10^3\ {\rm M}_\odot$) could plausibly be the outcome of stellar mergers in low metallicity ($Z<10^{-1}$~Z$_\odot$) and dense ($\gtrsim10^3\ {\rm M}_\odot\ {\rm pc}^{-3}$) stellar environments. These objects remain relevant as they can serve as the progenitors of intermediate-mass black holes and they are also formidable chemical polluter candidates, as evidenced by the peculiar abundances seen across cosmic history. This work investigates merger-induced mass loss in extremely massive stars within a hydrodynamic framework and provides a prescription derived from the simulations to estimate both the mass loss and the outcome of the interaction. We adapted the 1D hydrodynamic, stellar structure, and evolution code MESA to simulate stellar inspirals. In our simulations, we considered stars of $>1000\,\rm M_{\odot}$ with inspiraling companions of $<100$ M$_\odot$; hence, with mass ratios of $<0.1$. As the inspiral progresses, the orbital energy of the system is lost through the hydrodynamic and gravitational drag forces. This energy gets deposited as thermal energy in the extremely massive star's envelope. We find that the total ejected mass is $\sim$10-30$\%$ of the system's mass. Our results point out that most of the energy deposited by the inspiral is used to eject mass. These findings demonstrate that merger-induced mass loss is non-negligible for the considered configurations. Thus, it is an important process to account for when investigating the formation of extremely massive stars and predicting their possible role throughout cosmic history.
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