直接坍缩形成的黑洞的吸积
Accretion onto black holes formed by direct collapse
摘要：
在早期宇宙中形成大质量黑洞（BH）的一种可能的情况是，原始气体在原子冷却的暗物质晕中直接坍缩，其中气体无法通过分子跃迁有效冷却。我们研究的形成，这样的黑洞，以及吸积气体到这些对象和在吸积过程中发出的高能辐射，通过进行宇宙辐射流体动力学模拟。在没有辐射反馈的情况下，我们发现中心天体的吸积速率有一个上限，它是由热（~ 10^4 K）气体的初始坍缩形成的，其数量级为每年0.1 MSun。这足够形成一颗质量为10^5 MSun的超大质量恒星，它是BH的直接前身。假设这个质量的一小部分进入黑洞，我们跟踪随后的气体吸积到黑洞自洽与高能量辐射发射的吸积盘。使用射线跟踪算法来跟踪电离辐射的传播，我们详细模拟了吸积BH周围形成的光电离区域的演化。我们发现，质量为10^4 MSun的黑洞最初的吸积速度接近爱丁顿极限，但在大约10^6年后，由于黑洞附近的气体在强烈的光加热和辐射压力的作用下膨胀，吸积速度下降到爱丁顿极限的1%。与大质量的Pop III星形成相反，气体吸积到通过直接坍缩形成的BH上的一个标志是He II 1640发射的光度与H_alpha（或Ly_alpha）发射的光度之比极高;这可以被詹姆斯·韦伯太空望远镜探测到。最后，我们简要讨论了共同演化的黑洞和他们的宿主星系的影响。
英文摘要：
One possible scenario for the formation of massive black holes (BHs) in the early Universe is from the direct collapse of primordial gas in atomic-cooling dark matter haloes in which the gas is unable to cool efficiently via molecular transitions. We study the formation of such BHs, as well as the accretion of gas onto these objects and the high energy radiation emitted in the accretion process, by carrying out cosmological radiation hydrodynamics simulations. In the absence of radiative feedback, we find an upper limit to the accretion rate onto the central object which forms from the initial collapse of hot (~ 10^4 K) gas of the order of 0.1 MSun per year. This is high enough for the formation of a supermassive star, the immediate precursor of a BH, with a mass of the order of 10^5 MSun. Assuming that a fraction of this mass goes into a BH, we track the subsequent accretion of gas onto the BH self-consistently with the high energy radiation emitted from the accretion disk. Using a ray-tracing algorithm to follow the propagation of ionizing radiation, we model in detail the evolution of the photoionized region which forms around the accreting BH. We find that BHs with masses of the order of 10^4 MSun initially accrete at close to the Eddington limit, but that the accretion rate drops to of order 1 percent of the Eddington limit after ~ 10^6 yr, due to the expansion of the gas near the BH in response to strong photoheating and radiation pressure. One signature of the accretion of gas onto BHs formed by direct collapse, as opposed to massive Pop III star formation, is an extremely high ratio of the luminosity emitted in He II 1640 to that emitted in H_alpha (or Ly_alpha); this could be detected by the James Webb Space Telescope. Finally, we briefly discuss implications for the coevolution of BHs and their host galaxies.
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