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arXiv 1509.06975astro-ph.SRastro-ph.HEgr-qc
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合并中中子星潮汐p模g模不稳定性的增长率

Growth rate of the tidal p-mode g-mode instability in coalescing binary neutron stars

Nevin N. Weinberg

摘要:

最近,我们描述了由于p模到g模的非线性耦合引起的不稳定性,作为应用,我们研究了合并中的中子星的潮汐稳定性。虽然我们发现潮汐在螺旋早期是p-g不稳定的,并迅速将模式驱动到大能量,但我们的分析只考虑了三模相互作用。Venumadhav、Zimmerman和Hirata表明,四模相互作用也必须考虑在内,因为它们以相同的顺序进入分析。他们发现了三模和四模相互作用之间近乎精确的抵消,并得出结论,虽然双中子星中的潮汐可能是p-g不稳定的,但增长速度还不足以影响引力波信号。他们的分析假设线性潮汐是不可压缩的,这对静态线性潮汐(m=0谐波)是正确的,但对非静态线性潮汐(m=+/- 2)不是。在这里,我们占的非静态线性潮汐的可压缩性,并发现,三,四模式的相互作用不再取消。结果,我们发现不稳定性可以迅速驱动模式到显著的能量(在二元合并之前有几十个e折叠的增长时间)。我们还表明,线性阻尼干扰的取消,并可能进一步提高p-g增长率。不稳定性的早期开始(在引力波频率接近50 Hz时),快速的增长率和大量的不稳定模式(> 10^3)表明不稳定性可能会影响来自双中子星的引力波的相位演化。评估其影响需要了解不稳定性如何饱和,并留待未来工作。

英文摘要:

We recently described an instability due to the nonlinear coupling of p-modes to g-modes and, as an application, we studied the stability of the tide in coalescing binary neutron stars. Although we found that the tide is p-g unstable early in the inspiral and rapidly drives modes to large energies, our analysis only accounted for three-mode interactions. Venumadhav, Zimmerman, and Hirata showed that four-mode interactions must also be accounted for as they enter into the analysis at the same order. They found a near-exact cancellation between three- and four-mode interactions and concluded that while the tide in binary neutron stars can be p-g unstable, the growth rates are not fast enough to impact the gravitational wave signal. Their analysis assumes that the linear tide is incompressible, which is true of the static linear tide (the m=0 harmonic) but not the non-static linear tide (m=+/- 2). Here we account for the compressibility of the non-static linear tide and find that the three- and four-mode interactions no longer cancel. As a result, we find that the instability can rapidly drive modes to significant energies (there is time for several dozen e-foldings of growth before the binary merges). We also show that linear damping interferes with the cancellation and may further enhance the p-g growth rates. The early onset of the instability (at gravitational wave frequencies near 50 Hz), the rapid growth rates, and the large number of unstable modes (> 10^3), suggest that the instability could impact the phase evolution of gravitational waves from binary neutron stars. Assessing its impact will require an understanding of how the instability saturates and is left to future work.

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