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arXiv 1507.01940astro-ph.CO
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大星系团中的自相似能量学

Self-similar energetics in large clusters of galaxies

Francesco Miniati, Andrey Beresnyak

摘要:

大质量的星系团充满了炽热、动荡和磁化的团内介质。在引力不稳定性的作用下仍然形成,它们通过超音速流的吸积而增加质量。这些气流通过复杂的大尺度激波网络部分消散为热量[1],而剩余的跨音速气流则产生巨大的湍流涡流和级联[2,3]。湍流加热团簇内介质[4],并通过发电机作用放大磁能[5-8]。然而,调节重力能转化为动能、热能、湍流能和磁能的模式仍然未知。在这里,我们报告说,集群内介质的能量成分是有序的,根据一个永久的层次结构,其中热的比湍流的磁能密度保持几乎不变的整个集群的历史,尽管每个单独的组件和驱动器的湍流发电机均分的演变。这一结果围绕着质量吸积过程中释放的引力能产生湍流的近似恒定效率,这一点由我们的宇宙结构形成计算模型揭示[3,9]。这个层次的永久性特征反映了宇宙学中另一种类型的自相似性[10-13],而它的结构与当前的数据一致[14-18],编码了有关湍流加热和发电机作用效率的信息。

英文摘要:

Massive galaxy clusters are filled with a hot, turbulent and magnetized intra-cluster medium. Still forming under the action of gravitational instability, they grow in mass by accretion of supersonic flows. These flows partially dissipate into heat through a complex network of large-scale shocks [1], while residual transonic flows create giant turbulent eddies and cascades [2,3]. Turbulence heats the intra-cluster medium [4] and also amplifies magnetic energy by way of dynamo action [5-8]. However, the pattern regulating the transformation of gravitational energy into kinetic, thermal, turbulent and magnetic energies remains unknown. Here we report that the energy components of the intra-cluster medium are ordered according to a permanent hierarchy, in which the ratio of thermal to turbulent to magnetic energy densities remains virtually unaltered throughout the cluster's history, despite evolution of each individual component and the drive towards equipartition of the turbulent dynamo. This result revolves around the approximately constant efficiency of turbulence generation from the gravitational energy that is freed during mass accretion, revealed by our computational model of cosmological structure formation [3,9]. The permanent character of this hierarchy reflects yet another type of self-similarity in cosmology [10-13], while its structure, consistent with current data [14-18], encodes information about the efficiency of turbulent heating and dynamo action.

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