gravitational lensing

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The redirection or bending of light rays traveling in the gravitational field of an object, predicted by the general theory of relativity and commonly observed near massive objects like the sun, other stars, and distant galaxies.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun astronomy The action of a star that acts as a gravitational lens and focusses starlight from another star that passes behind it as observed from the Earth