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arXiv 1111.5424astro-ph.CO
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光子俘获使高红移半导体中黑洞种子超爱丁顿生长

Photon Trapping Enables Super-Eddington Growth of Black-Hole Seeds in Galaxies at High Redshift

Stuart Wyithe, Abraham Loeb

摘要:

我们确定了一种物理机制,它会导致z>6的星系中种子超大质量黑洞的快速,模糊的生长。具体来说,我们发现,在典型的高红移星系的中心密度的水平,邦迪吸积率意味着光子的扩散速度比引力下落速度慢,导致光子被困在吸积流和平流到黑洞。我们证明了存在一个黑洞质量范围(M_bh ~ 10^3-10^5太阳质量),在这个范围内,吸积流捕获辐射,对应于质量足够大以产生光子捕获吸积流的黑洞,但又足够小以使它们的邦迪半径不超过自引力气体的等温标度高度。在这些条件下,我们发现吸积达到远远超过爱丁顿速率的水平。对这种情况的预测是,z>6的活动星系核的X射线计数将在低光度处显示出截止值,对应于黑洞质量低于~10^5太阳质量。在低红移时,我们发现光子捕获并不重要,因为它只会发生在罕见的低自旋晕中,并且需要超过观测到的黑洞-晕质量关系的预期的黑洞质量。在高红移处,质量约为10^5太阳的种子黑洞的超爱丁顿增长可能为z~6-7的超大质量黑洞的增长提供了自然的加速,这距离大爆炸不到10亿年。

英文摘要:

We identify a physical mechanism that would have resulted in rapid, obscured growth of seed super-massive black-holes in galaxies at z>6. Specifically, we find that the density at the centre of typical high redshift galaxies was at a level where the Bondi accretion rate implies a diffusion speed of photons that was slower than the gravitational infall velocity, resulting in photons being trapped within the accretion flow and advected into the black-hole. We show that there is a range of black-hole masses (M_bh ~ 10^3-10^5 solar masses) where the accretion flow traps radiation, corresponding to black-holes that were massive enough to generate a photon trapping accretion flow, but small enough that their Bondi radii did not exceed the isothermal scale height of self-gravitating gas. Under these conditions we find that the accretion reaches levels far in excess of the Eddington rate. A prediction of this scenario is that X-ray number counts of active galactic nuclei at z>6 would exhibit a cutoff at the low luminosities corresponding to black-hole masses below ~10^5 solar masses. At low redshifts we find photon trapping to be unimportant because it could only occur in rare low spin halos, and would require black-hole masses in excess of expectations from the observed black-hole - halo mass relation. The super-Eddington growth of ~10^5 solar mass seed black-holes at high redshift may have provided a natural acceleration towards the growth of super-massive black-holes at z~6-7, less than a billion years after the Big Bang.

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