Formation of primordial supermassive stars by burst accretion
Formation of primordial supermassive stars by burst accretion
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DOI：
10.1093/mnras/stv1346
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发表时间：
2015-05
影响因子：
4.8
通讯作者：
Y. Sakurai;T. Hosokawa;N. Yoshida;H. Yorke
中科院分区：
文献类型：
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作者：
Y. Sakurai;T. Hosokawa;N. Yoshida;H. Yorke
最近的观测表明，超大质量黑洞（SMBHs）与10 - 9 M存在于红移z & 6;他们如何形成尚未得到解释。一个有前途的形成渠道是所谓的直接坍缩模型，它假定一个巨大的种子BH形式通过引力坍缩的10 - 5 M超大质量星星。我们研究了这样一个超大质量星星通过快速质量吸积生长的演化。在我们的计算中，内部恒星结构也是一致的。特别是，我们研究的影响依赖于时间的质量吸积的重复爆发和静止的阶段，预计将发生与自引力拱盘。我们表明，即使平均吸积率相同，这种幕式吸积的恒星演化与恒定吸积率的恒星演化在定性上是不同的。与恒定质量吸积的情况不同，星星的膨胀大致遵循R ' 2：6 10 3 R（M =100 M）1=2，原星星在吸积爆发之间的静止阶段可以大幅收缩。随着星星的收缩，恒星的辐射温度和电离光子发射率相应地增加，这会引起强烈的电离反馈，阻止质量吸积到星星上。在静止期tq的固定持续时间下，这种收缩发生在早期进化阶段，即M。10 3 M，tq' 10 3年。对于更晚的时期和更大的质量，但相同的tq，收缩是可以忽略不计的，即使在静止相。然而，随着静止时间tq的增加，即使质量更大的星星在静止阶段也会继续收缩。我们表明，这样的行为是很好地理解通过比较的间隔时间和膨胀的表面层的热弛豫时间。我们的结论是紫外辐射反馈是有效的
Recent observations show that supermassive black holes (SMBHs) with 10 9 M exist at redshift z & 6; how they form has yet to be explained. A promising formation channel is the so-called direct collapse model, which posits that a massive seed BH forms through gravitational collapse of a 10 5 M supermassive star. We study the evolution of such a supermassive star growing by rapid mass accretion. The internal stellar structure is also followed consistently in our calculation. In particular, we examine the impact of time-dependent mass accretion of repeating burst and quiescent phases that are expected to occur with a self-gravitating circumstellar disk. We show that the stellar evolution with such episodic accretion diers qualitatively from that expected with a constant accretion rate, even if the mean accretion rate is the same. Unlike the case of constant mass accretion, whereby the star expands roughly following R ’ 2:6 10 3 R (M =100 M ) 1=2 , the protostar can substantially contract during the quiescent phases between accretion bursts. The stellar eective temperature and ionizing photon emissivity increase accordingly as the star contracts, which can cause strong ionizing feedback and halt the mass accretion onto the star. With a xed duration of the quiescent phase tq, such contraction occurs in early evolutionary phases, i.e. for M . 10 3 M with tq’ 10 3 yr. For later epochs and larger masses but the same tq, contraction is negligible even during quiescent phases. With larger quiescent times tq, however, the star continues to contract during quiescent phases even for the higher stellar masses. We show that such behavior is well understood by comparing the interval time and the thermal relaxation time for a bloated surface layer. We conclude that the UV radiative feedback becomes eective