宇宙磁场

Cosmic magnetic fields

磁场在宇宙中无处不在,贯穿各种天体。磁场对天体形成、辐射和演化起重要作用,也是宇宙线研究的基础。以前人们对宇宙磁场的理解主要是来自对地球和太阳磁场的测量和物理解释。近20年来,对宇宙更大尺度天体的磁场测量取得很大进展:发现了银河系具备沿着银河旋臂的几万光年尺度磁场,强度为2-4μG;发现了银河系晕里具有环向磁场,在银道面上下方向相反;发现了银河系中心有极向磁场的观测证据;发现了邻近旋涡星系可能具有万光年尺度磁场的证据;发现了星系团几千万光年范围内磁场存在的证据。宇宙学模拟也显示在宇宙超大纤维结构中应该有磁场存在。这些磁场可能都是宇宙早期产生并在天体形成和演化过程中得以发扬光大。

Magnetic fields are ubiquitous in the universe,threading through all kinds of celestial bodies.They play a critical role in the formation,radiation and evolution of all kinds of these objects,and are an agent for cosmic ray propagation.Previously,our understanding of cosmic magnetic fields mainly came from observations and theoretical explanations of the solar and geomagnetic fields.In the last two decades,much progress has been made in the measurement of magnetic fields on larger scales:ordered magnetic fields along the spiral arms have been discovered in our Milky Way with a strength of 2―4 micro Gauss and a scale of several tens of thousand light years;toroidal magnetic fields have been found in the halo of the Milky Way with reversed directions below and above the Galactic plane;evidence for poloidal magnetic fields has been found near the center of the Galactic center;large-scale ordered fields with a scale length of several tens of thousand light years have also been revealed in nearby spiral galaxies and even in the clusters of galaxies with a scale length of tens of million light years.Simulations of cosmological structure formations also show that magnetic fields should exist in the filament structure.These magnetic fields are probably primodial fields generated in the early universe and then amplified during the formation and evolution of the structure and stars or galaxies.