It neither emits nor absorbs light significantly, which is why astronomers failed to notice it for millennia, even though dark matter contributes five times as much to the total mass of the universe as normal matter. It was only in the late twentieth century that careful study of the motion of normal, visible matter revealed the gravitational influence of lots of otherwise invisible stuff.
暗物质的“暗”并不是通常意义上的暗，而是彻底透明。它既不释放也不吸收光，因此几千年以来的天文学家一直忽略了这些物质的存在。直至 20 世纪后期，对普通可见物质运动规律的研究才揭示了大量不可见物质的重力影响。