In the constellation of Sagittarius, 27,000 light-years from Earth, a celestial chandelier burns with ancient light. NGC 6723, known as the Chandelier Cluster, is a globular cluster home to tens of thousands to millions of stars bound together by gravity—some of them over 10 billion years old, nearly as old as the universe itself.
For decades, astronomers assumed that all stars within such clusters formed simultaneously, like a single cosmic spark igniting everything at once. But the Hubble Space Telescope is rewriting that story. New observations of NGC 6723 reveal something surprising: the cluster's stars weren't born in one grand burst, but in two separate formation periods separated by 634 million years. That span might sound immense, but for a structure more than 10 billion years old, it's the equivalent of two heartbeats in the span of a human lifetime.
The discovery comes from two ambitious Hubble survey programs. The first, led by principal investigator Sarajedini, captured visible and near-infrared images of 65 globular clusters across our Milky Way, examining everything from stellar ages to how massive stars migrate toward a cluster's center while lighter stars drift outward. The second program, directed by Piotto, returned to many of those same clusters with Hubble's ultraviolet sensitivity, detecting subtle chemical variations that revealed hidden complexity in stellar populations.
Together, these observing programs have generated several hundred published research papers, transforming our understanding of these ancient stellar cities. More than 150 globular clusters orbit our galaxy, though astronomers suspect others remain hidden, obscured by dust or the crowded star fields around them.
The Chandelier Cluster now stands as a beacon of discovery. In a universe often defined by entropy and decay, here is a structure that has endured for over 10 billion years—and that still holds secrets about how galaxies form. Scientists may never fully recreate the conditions that birthed these ancient clusters, but with each observation, they're lighting their way closer to the answer.