More than 80 years ago, Albert Einstein made an astounding assertion: Gravity bends light. A clump of matter can act like an irregularly shaped piece of glass, altering the path of light rays from an object that lies behind it and creating a distorted image.
The material doing the distorting, an effect known as gravitational lensing, needn't be visible stars or galaxies. The unseen material known as dark matter, which astronomers believe pervades space and weighs 10 times as much as all the visible stuff, should also bend light (SN: 1/8/00, p. 30: A Dark View of the Universe).
Four teams of astronomers have now independently found signs of lensing due to dark matter, providing fresh evidence for the existence and distribution of this massive but unseen component of the cosmos.
Gathering the evidence required years of study. Dark matter typically elongates the image of a perfectly round galaxy by a tiny amount. Because no galaxy is exactly