Pinjian Chen

In Andromeda's stellar stream, a long ribbon of stars ripped from a small galaxy during a collision with a larger one, astronomers spotted a star that outshines all its neighbors. It pulsates, swelling and contracting every 89 days, like a heart beating in rhythm. Such stars are called Type II Cepheids, and this one is the brightest known.

A dense fog, through which only occasional headlight beams pierce. So it was in the early universe: young galaxies were wrapped in clouds of neutral hydrogen, which eagerly absorbed ultraviolet light. But sometimes gaps appeared in this shroud, and ionizing radiation burst out, making the cosmos transparent.