On the Apparent Dichotomy Between the Masses of Black Holes Inferred via X-rays and via Gravitational Waves
On the Apparent Dichotomy Between the Masses of Black Holes Inferred via X-rays and via Gravitational Waves
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关于通过 X 射线和引力波推断的黑洞质量之间明显的二分法
DOI：
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发表时间：
2019
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影响因子：
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通讯作者：
M. Cantiello
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作者：
R. Perna;Yihan Wang;N. Leigh;M. Cantiello
在通过黑洞合并时产生的引力波（GW）检测黑洞（BH）之前，在X射线双星中推断黑洞的存在，主要是通过动力学测量，测量质量在$\sim 5-20~M_\odot$之间。LIGO通过GWs发现的第一个黑洞是令人惊讶的，因为合并的两个黑洞的质量分别为35.6和28.6 $M_\odot$，这两个质量都超过了从X射线双星推断的范围。到目前为止，有10个二进制BH检测，很明显，虽然这两个分布不是不相交的，但它们肯定是不同的。在这封信中，我们认为，明显的二分法的原因是由于不同的形成渠道占主导地位：孤立的X射线双星演化，并在密集的星星集群的LIGO黑洞的动力学交换。我们表明，通过时间尺度的参数，在高质量的X射线双星的BH优先看到时，他们有较低的质量吸积。然后，我们进行高分辨率的N体模拟的一个集群的孤立BH与一系列的初始质谱，并表明BH二进制优先形成的最大质量的BH，此外，这些往往是最紧密的二进制文件（因此合并时间尺度较短）。我们还进行了模拟与中子星（NS）除了BH，更丰富的一个因素的5，并表明，形成的NS-BH的二进制是$< 1\%$的BH-BH的二进制，从而使动态形成的NS-BH系统的可能性比二进制BH的。
Prior to the detection of black holes (BHs) via the gravitational waves (GWs) they generate at merger, the presence of BHs was inferred in X-ray binaries, mostly via dynamical measurements, with measured masses in the range between $\sim 5-20~M_\odot$. The LIGO discovery of the first BHs via GWs was surprising in that the two BHs that merged had masses of 35.6 and 28.6 $M_\odot$, which are both above the range inferred from X-ray binaries. With 10 binary BH detections to date, it has become apparent that, while the two distributions are not disjoint, they are most certainly distinct. In this Letter, we suggest that the reason for the apparent dichotomy is due to a predominance of different formation channels: isolated binary evolution for X-ray binaries, and dynamical exchanges in dense star clusters for the LIGO BHs. We show, via timescale arguments, that BHs in high-masss X-ray binaries are preferentially seen when they have lower mass accretors. We then perform high-resolution N-body simulations of a cluster of isolated BHs with a range of initial mass spectra, and show that BH binaries are preferentially formed by the most massive BHs, and additionally that these tend to be the tightest binaries (hence with shorter merger timescales). We also perform a simulation with neutron stars (NSs) in addition to BHs, more abundant by a factor of 5, and show that the formation of NS-BH binaries is $< 1\%$ that of BH-BH binaries, hence making the dynamical formation of NS-BH systems much less likely than that of binary BHs.