Numerical analysis for merger of binary neutron stars in full general relativity

由两颗中子星组成的天体物理系统称为双中子星。这种近轨道的二元组发出引力波，导致轨道分离减少到合并。根据统计研究，这种合并每年发生一次，距离我们银河系50Mpc。在合并前的最后大约15分钟，超过10赫兹的引力波被发射出来。这种高频引力波是最有前途的引力波探测器来源之一，如LIGO。引力波形的预测是理论天体物理中的一个问题，双中子星合并后形成黑洞或超大质量中子星。如果形成一个被巨大的、热的、致密的环面包围的黑洞，它可能是伽马射线爆发的中心引擎。虽然这一假设已经提出了大约20年，但没有人知道它是否正确。弄清楚这个场景是否…是天体物理学中的重要问题之一。更多的里约是正确的或不正确的。基于这两个动机，我们在完全广义相对论中进行了两年的数值模拟。我们得出了以下结论。(1)如果总质量超过某一临界质量，则双中子星合并后形成黑洞。这取决于中子星的状态方程；对于看似合理的刚性核状态方程，临界质量是2.6-2.8个太阳质量。(2)如果总质量小于临界质量，则形成椭圆形的HMN。由于它的椭圆形状，HMNS发出引力波并耗散角动量。由于离心力的减小，HMNS在大约100毫秒内坍塌成一个黑洞。(3)如果双中子星的质量比不是1，则在黑洞周围形成吸积环。但即使在质量比为2/3的情况下，环面质量也约为太阳质量的10%。(4)对于黑洞的形成，在最后时刻发出了与准正则模环相关的引力波，在50Mpc的距离处，振幅约为10^&lt；-23&gt；，频率约为7 kHz。除非合并发生在我们银河系周围，否则很难探测到这样的引力波。(5)在HMN形成的情况下，由于椭圆HMN的旋转而发出准周期引力波。在50 MpC的距离上，有效振幅约为10°~(-20)，频率约为3 kHz。这种引力波可能会被下一代探测器探测到。(6)不等质量双星合并后，形成一个被大质量环面包围的黑洞。这样的系统是伽马射线爆发中心引擎的候选系统。较少

Astrophysical systems of two neutron stars are referred to as binary neutron stars. Such binary of close orbits emits gravitational waves, resulting in decreasing the orbital separation to merger. According to statistical studies, the merger happens once a year in a distance of 50 Mpc around our Galaxy. In the last about 15 minutes just before the merger, gravitational waves of more than 10Hz is emitted. Such high frequency gravitational waves are among the most promising sources of gravitational wave detector such as LIGO. Predicting the gravitational waveforms is an issue in theoretical astrophysics.After merger of binary neutron stars, a black hole or a hypermassive neutron star (HMNS) is formed. If a black hole surrounded by massive, hot, and dense torus is formed, it may be a central engine of gamma-ray burst. Although this hypothesis has been proposed for about 20 years, no one knows if it is correct. It is one of the important issues in astrophysics to clarify whether this scena … More rio is correct or not.By these two motivations, we have performed numerical simulations in full general relativity for two years. We have reached the following conclusion. (1) A black hole is formed after merger of binary neutron stars if the total mass exceeds a critical mass. It depends on the equation of state of neutron stars ; for plausible stiff nuclear equations of state, the critical mass is 2.6-2.8 solar mass. (2) If the total mass is smaller than the critical mass, an HMNS of elliptical shape is formed. Because of its elliptic shape, the HMNS emits gravitational waves and dissipates angular momentum. As a result of the reduced centrifugal force, the HMNS collapses to a black hole in about 100 ms. (3) Accretion torus is formed around a black hole if the mass ratio of binary neutron stars is not unity. But even for the mass ratio 2/3, the torus mass is about 10% of the solar mass. (4) For the black hole formation, gravitational waves associated with the quasinormal mode ringing are emitted in the last moment.The amplitude is about 10^<-23> at a distance of 50 Mpc and the frequency is about 7 kHz. It is very difficult to detect such gravitational waves unless the merger happens around our Galaxy by chance. (5) In the case of HMNS formation, quasiperiodic gravitational waves are emitted due to rotation of elliptic HMNS. The effective amplitude is about 10^<-20> at a distance of 50 Mpc and the frequency is about 3 kHz. Such gravitational waves may be detected by the next-generation detectors. (6) After merger of unequal mass binaries, a black hole surrounded by a massive torus is formed. Such system is a candidate of the central engine of gamma-ray bursts. Less