Xiaodian 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.

The cosmological orchestra doesn't tune to a single tuning fork. There are two groups of instruments: one listens to the hum of the young universe — the cosmic microwave background, while the other reads notes from mature galaxies and supernovae.

In 2008, the Spitzer telescope aimed at the star HD 15407A and detected a strong infrared excess. Fifteen years later, in 2023, JWST repeated the measurements. The light from the dust had dimmed by 14%. But the mineral composition of the dust remained the same, like a fingerprint taken in different years.

An old lighthouse at the edge of the harbor blinks with the precision of a clockwork mechanism. Every few hours its lamp flares and dims, and sailors recognize that rhythm from afar, using the strength of the light to tell where the shore lies.