引力透镜效应与暗物质探测*

引力透镜是广义相对论引申的强引力场中特殊的光学效应。20世纪80年代以来，天文观测发现了许多引力透镜效应的实例，包括“爱因斯坦环”。一些本来很难探测的非常遥远、非常暗弱的天体，幸亏引力透镜效应而进入当代天文学家的视野。“大爆炸”70万年以后，宇宙处于延续4～5亿年的“黑暗年代”，物质大体呈均匀结构，没有任何自主发光的天体。星光灿烂的辉煌时期始于何时？引力透镜效应的观测给出了相关信息。被称为21世纪“两朵乌云”之一的暗物质，比所有人类已知物质的总量多4倍以上，不发出任何辐射，不可能被直观测到。引力透镜效应作为发现宇宙暗物质的探针，在寻找暗物质确实存在的直接证据和分析暗物质的空间分布方面作出了贡献。

Gravitational Lensing and Detection of Dark Matter

According to the general theory of relativity, gravitational lensing occurs when light from the distant objects is distorted and magnified in a strong gravitational field. Many examples of gravitational lensing, including Einstein rings, have been discovered since 1980. Thanks to gravitational lensing, today's astronomers can catch sight of celestial bodies that are too far away to be observed. 700 000 years past after the Big Bang, the universe lasted next 400-500 million years when it was in dark, with the matters homogeneous in general. There were not any objects that shone. When did stars begin to emit light? From gravitational lensing, astronomers have got some information about it. Dark matter, one of two dark clouds called in 21st century, is over 4 times in mass more than whole matter we have ever known, and radiate nothing, so it is impossible to be detected directly. By means of gravitational lensing, however, we can obtain the evidence to prove the presence of such dark matter and analyze the space distribution.