globular-clusters

Determining a star's age is one of astronomy's most difficult problems — stars carry no birth certificates. Astronomers use stellar evolution models, colour-magnitude diagrams of star clusters, radioactive isotope ratios, asteroseismology (listening to stars vibrate), and gyrochronology (how stars spin down with age). The oldest stars in the Milky Way are 13.5 billion years old — almost as old as the universe itself.

Globular clusters are the oldest and densest stellar systems in the universe — spherical swarms of hundreds of thousands of stars bound together for billions of years. Here's how they form, what they reveal about galactic history, and why they remain one of astronomy's most productive laboratories.