Shock waves in tidally compressed stars by massive black holes
Shock waves in tidally compressed stars by massive black holes
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DOI：
10.1051/0004-6361:20078264
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发表时间：
2007-07
影响因子：
6.5
通讯作者：
M. Brassart;J. Luminet
中科院分区：
文献类型：
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作者：
M. Brassart;J. Luminet
目标。我们研究了主序星深入穿透大质量黑洞潮汐半径的情况。我们关注的是压缩阶段，这会导致恒星在最大压缩时刻形成所谓的煎饼形状。其目的是研究潮汐压缩过程，特别关注激波的发展，推导出与煎饼星有关的热力学参数的可靠估计，并解决关于是否可以在潮汐压缩恒星的核心引发热核反应的争议。方法：研究方法。我们建立了一个与问题的几何形状相适应的一维流体动力学模型。基于高分辨率的Godunov激波捕获型方法，该模型允许我们研究恒星在与其轨道平面垂直的方向上的压缩相。结果。我们证明了两个区域的存在取决于冲击波是在最大核压缩瞬间之前还是之后发展的。在这两种情况下，我们都证实了恒星核心中的高压缩系数和高加热系数能够引发热核爆炸。此外，我们还表明，激波将一个短暂但非常高的温度峰值从恒星的中心向外携带到恒星的表面。我们初步得出结论，这种现象可能会引起硬电磁辐射，与在其宿主星系中已经观察到的一些伽玛暴类型的耀斑相比。最后，我们估计煎饼星的速率应该是每个星系每年大约10−5。如果是在硬X射线或γ波段中产生的，每年应该可以在整个可观测宇宙中探测到几次这类事件。
Aims. We investigate the case of a main-sequence star deeply penetrating the tidal radius of a massive black hole. We focus on the compression phase leading to a so-called pancake configuration of the star at the instant of greatest compression. The aim is to study the tidal compression process paying particular attention to the development of shock waves, to deduce reliable estimates of the thermodynamical quantities involved in the pancake star, and to solve a controversy about whether thermonuclear reactions can be triggered in the core of a tidally compressed star. Methods. We set up a one-dimensional hydrodynamical model adapted to the geometry of the problem. Based on the high-resolution shock-capturing Godunov-type approach, this model allows us to study the compression phase of the star in a direction orthogonal to its orbital plane. Results. We show the existence of two regimes depending on whether shock waves develop before or after the instant of maximum core compression. In both cases we confirm that high compression and heating factors in the stellar core are able to trigger a thermonuclear explosion. Moreover, we show that the shock waves carry a brief but very high peak of temperature outwards from the centre to the surface of the star. We tentatively conclude that the phenomenon could give rise to hard electromagnetic radiation, to be compared to some GRB-type flares already observed in their host galaxies. Finally, we estimate that the rate of pancake stars should be about 10 −5 per galaxy per year. If generated in hard X- or γ-ray bands, several events of this kind per year should be detectable within the full observable universe.