Sahu K C, Casertano S, Livio M, Gilliland R L, Panagia N, Albrow M D, Potter M
Space Telescope Science Institute, Baltimore, MD 21218, USA.
Nature. 2001 Jun 28;411(6841):1022-4. doi: 10.1038/35082507.
Gravitational microlensing offers a means of determining directly the masses of objects ranging from planets to stars, provided that the distances and motions of the lenses and sources can be determined. A globular cluster observed against the dense stellar field of the Galactic bulge presents ideal conditions for such observations because the probability of lensing is high and the distances and kinematics of the lenses and sources are well constrained. The abundance of low-mass objects in a globular cluster is of particular interest, because it may be representative of the very early stages of star formation in the Universe, and therefore indicative of the amount of dark baryonic matter in such clusters. Here we report a microlensing event associated with the globular cluster M22. We determine the mass of the lens to be 0.13(+0.03)(-0.02) solar masses. We have also detected six events that are unresolved in time. If these are also microlensing events, they imply that a non-negligible fraction of the cluster mass resides in the form of free-floating planetary-mass objects.
引力微透镜提供了一种直接测定从行星到恒星等各类天体质量的方法，前提是能够确定透镜天体和源天体的距离及运动情况。在银河系中心致密恒星场背景下观测到的球状星团为此类观测提供了理想条件，因为发生微透镜效应的概率很高，且透镜天体和源天体的距离及运动学特征受到很好的限制。球状星团中低质量天体的丰度尤其令人关注，因为它可能代表了宇宙中恒星形成的极早期阶段，因此也能指示此类星团中暗重子物质的数量。在此，我们报告了一起与球状星团M22相关的微透镜事件。我们确定透镜天体的质量为0.13（+0.03）（-0.02）个太阳质量。我们还探测到六个时间上无法分辨的事件。如果这些也是微透镜事件，那就意味着该星团质量中不可忽略的一部分以自由漂浮的行星质量天体的形式存在。
