The dynamic ejecta of compact object mergers and eccentric collisions
The dynamic ejecta of compact object mergers and eccentric collisions
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DOI：
10.1098/rsta.2012.0272
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发表时间：
2012-10
期刊：
影响因子：
--
通讯作者：
S. Rosswog
中科院分区：
文献类型：
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作者：
S. Rosswog
紧凑的天体合并以多种方式喷射出富含中子的物质：通过由引力扭矩中介的动态喷射，如中微子驱动的风，可能也有很大一部分最终通过粘滞和核过程的结合而脱离束缚。如果紧凑的双星合并确实会产生伽马射线暴，那么也应该有一个相互作用区域，在那里超相对论性流出物与中微子驱动的风相互作用，并产生适度的相对论性抛射物。每种类型的抛射物具有不同的物理性质，因此对核合成和紧凑型物体碰撞时产生的电磁瞬变起着不同的作用。在这里，我们专注于动态抛射，并介绍了30多个流体动力学模拟的结果，这些模拟包括引力波驱动的合并和抛物相遇，因为它们可能发生在球状星团中。我们发现，合并喷射出的极富含中子的物质大约是太阳质量的1%。确切的数量，以及弹射速度，取决于不对称系统的相关质量，以更高的速度弹射更多的物质。这种物质经历了一个强大的r过程，其喷出量和丰度模式与中子星合并是“重”（a >130） r过程同位素的主要来源一致。抛物线碰撞，尤其是中子星和黑洞之间的碰撞，会喷射出大量的质量，因此，如果不产生过多的临界r过程物质，就不会频繁发生。我们还讨论了由抛射物内的放射性衰变（“巨新星”）提供动力的电磁瞬变，以及当抛射物在环境介质中消散其大动能时出现的射电耀斑。
Compact object mergers eject neutron-rich matter in a number of ways: by the dynamical ejection mediated by gravitational torques, as neutrino-driven winds, and probably also a good fraction of the resulting accretion disc finally becomes unbound by a combination of viscous and nuclear processes. If compact binary mergers indeed produce gamma-ray bursts, there should also be an interaction region where an ultra-relativistic outflow interacts with the neutrino-driven wind and produces moderately relativistic ejecta. Each type of ejecta has different physical properties, and therefore plays a different role for nucleosynthesis and for the electromagnetic (EM) transients that go along with compact object encounters. Here, we focus on the dynamic ejecta and present results for over 30 hydrodynamical simulations of both gravitational wave-driven mergers and parabolic encounters as they may occur in globular clusters. We find that mergers eject approximately 1 per cent of a Solar mass of extremely neutron-rich material. The exact amount, as well as the ejection velocity, depends on the involved masses with asymmetric systems ejecting more material at higher velocities. This material undergoes a robust r-process and both ejecta amount and abundance pattern are consistent with neutron star mergers being a major source of the ‘heavy’ (A>130) r-process isotopes. Parabolic collisions, especially those between neutron stars and black holes, eject substantially larger amounts of mass, and therefore cannot occur frequently without overproducing gala- ctic r-process matter. We also discuss the EM transients that are powered by radioactive decays within the ejecta (‘macronovae’), and the radio flares that emerge when the ejecta dissipate their large kinetic energies in the ambient medium.