Formation of Ultracompact X-Ray Binaries in Dense Star Clusters
Formation of Ultracompact X-Ray Binaries in Dense Star Clusters
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DOI：
10.1086/429220
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发表时间：
2005-01
期刊：
影响因子：
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通讯作者：
N. Ivanova;F. Rasio;J. Lombardi, Jr.;K. Dooley;Z. Proulx
中科院分区：
文献类型：
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作者：
N. Ivanova;F. Rasio;J. Lombardi, Jr.;K. Dooley;Z. Proulx
在致密的星星团（如银河系球状星团）中观察到的明亮、超紧凑的X射线双星，一定是相对最近形成的，因为它们作为持久亮源的寿命很短（例如，对于从初始质量约为0.2 M的简并氦伴星吸积的1.4 M中子星星，在1036 ergs-1以上约为108 yr）。因此，我们可以利用目前的条件在一个集群的核心，研究可能的动力学形成过程中，这些来源。在这里，我们表明，中子星和红巨星之间的直接物理碰撞可以提供一个足够的形成率来解释观测到的亮源数量。这些碰撞产生紧密的、偏心的中子星-白矮星双星，它们通过引力辐射在约106-1010年的时间尺度上衰变到接触，通常比星团的年龄更短。
Bright, ultracompact X-ray binaries observed in dense star clusters, such as Galactic globular clusters, must have formed relatively recently, since their lifetimes as persistent bright sources are short (e.g., ~108 yr above 1036 ergs s-1 for a 1.4 M☉ neutron star accreting from a degenerate helium companion with an initial mass of ~0.2 M☉). Therefore, we can use the present conditions in a cluster core to study possible dynamical formation processes for these sources. Here we show that direct physical collisions between neutron stars and red giants can provide a sufficient formation rate to explain the observed numbers of bright sources. These collisions produce tight, eccentric neutron star-white dwarf binaries that decay to contact by gravitational radiation on timescales ~106-1010 yr, usually shorter and often much shorter than the cluster age.