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arXiv 0912.4262astro-ph.CO
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星系合并中多尺度气体流入直接形成超大质量黑洞

Direct Formation of Supermassive Black Holes via Multi-Scale Gas Inflows in Galaxy Mergers

Lucio Mayer, Stelios Kazantzidis, Andres Escala, Simone Callegari

摘要:

对遥远的明亮类星体的观测表明,在大爆炸后不到10亿年的时间里,就已经存在了10亿个太阳质量的超大质量黑洞。光黑洞种子由原始无金属恒星坍缩形成的模型不能解释它们由于低效的气体吸积而迅速出现。或者,这些黑洞可能是由原星系中心的气体直接坍缩形成的。然而,这需要不含金属的气体,不能有效冷却,因此不会变成恒星,与原星系的快速金属富集形成对比。在这里,我们用数值模拟来表明,大规模的原星系之间的合并自然产生所需的中央气体积累,而不需要抑制恒星的形成。合并驱动的气体流入产生了不稳定的、巨大的核气体盘。在圆盘内,第二次气体流入在十万年内在亚秒差距尺度的云中积累了超过1亿太阳质量的气体。星云会经历引力坍缩,最终导致大质量黑洞的形成。黑洞可以在不到10亿年的时间里通过吸积周围圆盘中的气体成长到10亿个太阳质量。

英文摘要:

Observations of distant bright quasars suggest that billion solar mass supermassive black holes (SMBHs) were already in place less than a billion years after the Big Bang. Models in which light black hole seeds form by the collapse of primordial metal-free stars cannot explain their rapid appearance due to inefficient gas accretion. Alternatively, these black holes may form by direct collapse of gas at the center of protogalaxies. However, this requires metal-free gas that does not cool efficiently and thus is not turned into stars, in contrast with the rapid metal enrichment of protogalaxies. Here we use a numerical simulation to show that mergers between massive protogalaxies naturally produce the required central gas accumulation with no need to suppress star formation. Merger-driven gas inflows produce an unstable, massive nuclear gas disk. Within the disk a second gas inflow accumulates more than 100 million solar masses of gas in a sub-parsec scale cloud in one hundred thousand years. The cloud undergoes gravitational collapse, which eventually leads to the formation of a massive black hole. The black hole can grow to a billion solar masses in less than a billion years by accreting gas from the surrounding disk.

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