Hubble's Chandelier Cluster Reveals Star Formation in Closely Spaced Bursts

The image is the product of two coordinated observing programs. The first, led by astronomer Anto Sarajedini, surveyed 65 Milky Way globular clusters using visible and near-infrared light. This large-scale survey was designed to characterize globular cluster properties by studying their stellar populations .

A second team, led by Giampaolo Piotto, conducted a follow-up study using ultraviolet light . The UV data was key: it allowed the team to resolve differences in stellar chemistry and timing that visible light alone could not distinguish.

Evidence of Multiple Star Formation Episodes

By combining the visible, near-infrared, and ultraviolet data, Piotto's team found that NGC 6723 — a cluster more than 10 billion years old — experienced two closely spaced periods of star formation. Those episodes occurred within 634 million years of each other .

This finding is significant. For decades, astronomers assumed globular clusters formed in a single, dramatic burst of star formation early in the universe's history. The detection of "multiple stellar populations" with such a small age difference — resolvable even within a 10-billion-year-old object — provides direct evidence that clusters built up their stars in rapid succession rather than in one event .

Why It Matters for Understanding Globular Clusters

Globular clusters are among the oldest objects in the Milky Way. Astronomers know of more than 150 such clusters in our galaxy, each containing tens of thousands to millions of stars bound tightly by gravity . Because they preserve a record of the early universe's star-forming conditions, understanding how they formed is crucial to models of galaxy assembly.

The ability to distinguish age differences of only a few hundred million years within a 10-billion-year-old system gives researchers a new tool. It supports the "multiple population" paradigm of globular cluster formation, which posits that successive generations of stars enriched the cluster's gas, triggering subsequent rounds of star birth .

The Chandelier Cluster, named for its resemblance to a chandelier filled with countless lights — where each lightbulb is an individual star — now also serves as a laboratory for understanding the first chapters of stellar and galactic evolution .