Astronomy
Gravitational Lensing and Its Uses
Quick fact
A single faraway galaxy bent by a massive cluster can appear as multiple images — and sometimes as a perfect or near-perfect ring of light, called an Einstein ring, predicted by Einstein's theory of general relativity.
Why this is interesting
You have probably seen distorted images in a funhouse mirror — but did you know that entire galaxies can act as giant natural lenses, bending light around them in space? How can something invisible, like black holes or dark matter, be 'seen' using only light?