超大质量黑洞周围双星碰撞率研究
On the rates of binary star collisions around hypermassive black holes
- Monash University（莫纳什大学）
- OzGrav: Australian Research Council Centre of Excellence for Gravitational Wave Discovery（澳大利亚研究委员会引力波发现卓越中心）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究通过蒙特卡洛模拟发现，超大质量黑洞周围主序双星碰撞可产生可观测瞬变，估计LSST每年可探测数千个此类事件，为核瞬变研究提供新途径。
AI中文摘要：
对银河系的观测表明，星系中心存在双星。我们利用蒙特卡洛模拟，对这类双星与星系中心黑洞（质量范围为10^5-10^10太阳质量，其中质量>=10^8太阳质量的黑洞称为超大质量黑洞HMBHs）相遇的群体统计进行了建模。虽然主序单星在超大质量黑洞周围不会发生潮汐瓦解事件，但主序双星的恒星碰撞可能产生可观测的瞬变现象。我们使用了三体代码Multistar中实现的后牛顿爱因斯坦-因费尔德-霍夫曼（EIH）方程。我们针对六个黑洞质量和十种不同的双星参数分布，每种情况模拟了100,000个模型。我们发现所有模型中均发生恒星碰撞，碰撞比例从圆形等质量双星的约7%到观测驱动的Moe2017双星分布的约0.2%不等。大多数碰撞发生在顺行、紧密双星且低撞击参数beta = r_t/r_p的情况下，此时黑洞的潮汐力在近心点通过期间驱动双星偏心率增大。对于较低质量黑洞（<=10^8太阳质量），碰撞速度接近双星逃逸速度，但对于较高质量黑洞，碰撞速度范围更广，这意味着恒星并合比例增加。利用经验损失锥速率和局部黑洞质量函数，我们估计对于Kroupa质量函数、Opik定律、倾斜轨道模型和MS17模型，在10^6太阳质量黑洞周围，LSST可探测的碰撞率分别约为每年8,600和3,000个事件；在10^8太阳质量黑洞周围，分别约为每年330和150个事件；在10^9太阳质量黑洞周围，分别约为每年3.5和2.8个事件。这些结果表明，超大质量黑洞周围的双星碰撞代表了一类潜在可观测的核瞬变群体，可能对宽视场光学巡天探测到的日益增多的模糊核瞬变样本有所贡献。
英文摘要：
Observations of the Milky Way show that galaxies have binary stars in their centres. Using Monte Carlo simulations, we model the population statistics of encounters of such binaries with galactic central black holes (BHs) of mass 10^5-10^{10} Msun (hypermassive BHs >= 10^8 Msun HMBHs). Whereas main-sequence single stars cannot undergo tidal disruption events around HMBHs, stellar collisions of main-sequence binary stars may produce observable transients. We use the post-Newtonian Einstein-Infeld-Hoffmann (EIH) equations as implemented in the three-body code Multistar. We simulate 100,000 models each for six BH masses and 10 different binary parameter distributions. We find that stellar collisions occur in all models, with collision fractions ranging from ~7% for circular, equal-mass binaries to ~0.2% for the observationally motivated Moe2017 binary distribution. Most collisions occur for prograde, tight binaries at low impact parameters beta = r_t/r_p, where the tidal force of the BH drives up the binary eccentricity during pericentre passage. Collision velocities are close to the binary escape velocity for lower-mass BHs (<= 10^8 Msun), but span a wider range for higher-mass BHs, implying an increasing fraction of stellar mergers. Using empirical loss-cone rates and the local BH mass function, we estimate detectable LSST collision rates of ~8,600 and ~3,000 events per year for our Kroupa mass function, Opik's law, inclined orbit model and our MS17 model, respectively, around 10^6 Msun BHs; ~330 and ~150 events per year around 10^8 Msun BHs; and ~3.5 and ~2.8 events per year around 10^9 Msun BHs. These results suggest that binary stellar collisions around HMBHs represent a potentially observable population of nuclear transients that may contribute to the growing sample of ambiguous nuclear transients detected by wide-field optical surveys.
