The Relative Stability against Merger of Close, Compact Binaries
The Relative Stability against Merger of Close, Compact Binaries
复制标题
针对紧密、紧凑的二进制文件合并的相对稳定性
DOI：
10.1086/304861
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
J. E. Tohline
中科院分区：
文献类型：
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作者：
K. New;J. E. Tohline
由于引力辐射的发射，致密双星的轨道间隔会随着时间的推移而缩小。双星系统演化的这个螺旋阶段通常会比系统的轨道周期长得多，但最终的合并可能是动态的，并且在很大程度上受到流体动力学效应的驱动，特别是如果存在临界分离，系统在合并时变得动态不稳定。事实上，如果弱相对论性系统（例如白色矮-白色矮双星）在某个临界距离处遇到动力学不稳定点，合并可能完全是一个经典的流体动力学过程。因此，对这一阶段双星演化的适当研究必须包括三维流体动力学模拟。我们构造了同步旋转的平衡序列，等质量的双星在圆轨道上与一个单一的参数-二进制分离变化沿着每个序列。序列已被构造与各种多变以及现实的白色矮星和中子星星的状态方程。使用牛顿，有限差分流体力学代码，我们已经检查了动态稳定性的个别模型沿着这些平衡序列。我们的模拟表明，没有不稳定点存在的序列，我们分析，有相对较软的状态方程（多变指数n = 1.0和1.5的多变序列和两个白色矮星序列）。然而，我们确定了动态不稳定的二元模型的状态方程较硬的序列（n = 0.5多方序列和两个中子星星序列）。因此，我们推断，软状态方程的二进制系统不会被驱动合并的动力学不稳定性。对于n = 0.5多变序列，动力学不稳定性发生的分离似乎与序列沿着的最小能量和角动量配置有关。我们的模拟表明，但没有最终证明，在相对论效应的情况下，这种相同的关联也可能适用于双中子星星系统。
The orbital separation of compact binary stars will shrink with time owing to the emission of gravitational radiation. This inspiral phase of a binary system's evolution generally will be very long compared to the system's orbital period, but the final coalescence may be dynamical and driven to a large degree by hydrodynamic effects, particularly if there is a critical separation at which the system becomes dynamically unstable toward merger. Indeed, if weakly relativistic systems (such as white dwarf-white dwarf binaries) encounter a point of dynamical instability at some critically close separation, coalescence may be entirely a classical, hydrodynamic process. Therefore, a proper investigation of this stage of binary evolution must include three-dimensional hydrodynamic simulations. We have constructed equilibrium sequences of synchronously rotating, equal-mass binaries in circular orbit with a single parameter—the binary separation—varying along each sequence. Sequences have been constructed with various polytropic as well as realistic white dwarf and neutron star equations of state. Using a Newtonian, finite-difference hydrodynamics code, we have examined the dynamical stability of individual models along these equilibrium sequences. Our simulations indicate that no points of instability exist on the sequences we analyzed that had relatively soft equations of state (polytropic sequences with polytropic index n = 1.0 and 1.5 and two white dwarf sequences). However, we did identify dynamically unstable binary models on sequences with stiffer equations of state (n = 0.5 polytropic sequence and two neutron star sequences). We thus infer that binary systems with soft equations of state are not driven to merger by a dynamical instability. For the n = 0.5 polytropic sequence, the separation at which a dynamical instability sets in appears to be associated with the minimum energy and angular momentum configuration along the sequence. Our simulations suggest but do not conclusively demonstrate that, in the absence of relativistic effects, this same association may also hold for binary neutron star systems.