坍缩超壳层中球状星团的形成
Globular Cluster formation in a collapsing supershell
摘要：
原始云被认为是所谓的第三星族恒星的宿主。这些恒星非常巨大，完全不含金属。质量在130到260太阳质量之间的第三星族恒星的生命的最后阶段是一个非常有活力的超新星爆炸。一颗超新星驱动一个激波，在激波后面形成一个球对称的非常致密的超壳层，它可能会变得引力不稳定，碎片化，形成恒星。在本文中，我们研究了在什么条件下膨胀的超壳层会变得引力不稳定，以及这些超壳层恒星（SSSs）的反馈如何影响它的周围环境。我们模拟，通过一个1-D的欧拉水代码，原始云的早期演变后，超新星爆炸，SSSs的形成，以及随后的演变，一旦SSSs开始释放能量和重元素到星际介质。我们的研究结果表明，壳，丰富的核合成产物从SSSs，向内传播，对原始云的中心。在几百万年的时间跨度内，这个向内传播的壳层到达距离原始云中心只有几秒差距的地方。它的密度极高，温度极低，因此具备了新一轮恒星形成的条件。我们研究这两个不同的恒星群体中有多少部分可以保持结合并存活到今天。我们还研究了在什么条件下这个过程可以重复并形成多个恒星星族。我们广泛地讨论了所提出的方案是否有助于解释球状星团形成机制的一些悬而未决的问题。
英文摘要：
Primordial clouds are supposed to host the so-called population III stars. These stars are very massive and completely metal-free. The final stage of the life of population III stars with masses between 130 and 260 solar masses is a very energetic hypernova explosion. A hypernova drives a shock, behind which a spherically symmetric very dense supershell forms, which might become gravitationally unstable, fragment, and form stars. In this paper we study under what conditions can an expanding supershell become gravitationally unstable and how the feedback of these supershell stars (SSSs) affects its surroundings. We simulate, by means of a 1-D Eulerian hydrocode, the early evolution of the primordial cloud after the hypernova explosion, the formation of SSSs, and the following evolution, once the SSSs start to release energy and heavy elements into the interstellar medium. Our results indicate that a shell, enriched with nucleosynthetic products from SSSs, propagates inwards, towards the center of the primordial cloud. In a time span of a few Myr, this inward-propagating shell reaches a distance of only a few parsec away from the center of the primordial cloud. Its density is extremely high and its temperature very low, thus the conditions for a new episode of star formation are achieved. We study what fraction of these two distinct populations of stars can remain bound and survive until the present day. We study also under what conditions can this process repeat and form multiple stellar populations. We extensively discuss whether the proposed scenario can help to explain some open questions of the formation mechanism of globular clusters.
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