Evan N. Kirby

In the dense swarm of old stars known as the globular cluster M15, astronomers have spotted not just stars but layers of time. Some stars were born earlier, others later, and their chemical composition reveals their origin with the precision of an archaeologist reading the strata of an ancient settlement.

On the outskirts of the Milky Way, tiny stellar systems hide, so faint that even powerful telescopes barely spot them. Until recently, astronomers knew almost nothing about these objects, dubbed ultra-faint compact satellites.

Imagine a forest planted in a single day. At first glance, all trees look alike, but their cross sections tell different stories: some grew on clean soil, others on the ashes of ancient fires.