Hubble Captures a 10-Billion-Year-Old Star Cluster That Sparkles Like a Distant Chandelier

Hubble has delivered a crisp new view of NGC 6723, a globular cluster tucked in the constellation Sagittarius. The image shows a tight swarm of stars that fills the frame with countless points of light, each one a distinct sun shining across 27,000 light-years of space. Blue stars crowd the center while warmer orange stars appear more often near the edges, and many of the brighter ones carry the sharp, cross-shaped spikes created by the telescope’s optics.

Globular clusters are some of the Milky Way’s oldest structures, containing a wealth of ancient history and celestial knowledge. We have one in particular, NGC 6723, which originated over 10 billion years ago and is still going strong, with tens of thousands to millions of stars gravitationally linked together in a roughly spherical shape. As you move through this region, you can’t help but notice how dense and brilliant everything is, as the stars are far away from those near the Sun and move through a much smaller volume of space.

For a long time, scientists believed that these clusters created all of their stars in a single huge burst, but this was before Hubble got involved. New data from the reliable space telescope has thrown that notion out the window for NGC 6723. It turns out that there were two independent rounds of star creation, the second of which began only 634 million years after the first. That may not seem like much, but given the age of this object, it’s more like a brief halt in the big scheme of things, demonstrating that globular clusters have more complex histories than the older model anticipated.

Hubble gathered the raw data through two coordinated programs. The first examined 65 globular clusters using visible and near-infrared light, allowing researchers to observe how heavier stars shift towards the center over time while lighter stars drift away. A follow-up experiment adds UV sensitivity to the combination, allowing it to detect variations in the stars’ chemical makeup and sharpen the timeframe of those two formation phases.

The colors in the image aren’t simply for show, as they also offer information about the stars in the cluster. The hotter, bluer stars are usually younger or have been impacted by close encounters with other stars or mergers deep within the cluster’s dense core. The cooler, orange stars, on the other hand, are frequently older, having emerged from the main sequence and developed into the giants you see before you. The contrast between these two populations gives the cluster a layered appearance and reveals information about the mechanisms that caused its creation.

NGC 6723 is located in the Milky Way’s halo, not the flat disk around which the Sun orbits. That’s significant because clusters like this one presumably formed before the galaxy took on its current shape. This shows that the stars in this cluster have some of the earliest chemical traces from our galaxy’s first star formation generations. Studying them in this way helps us to track how the Milky Way grew from its basic building blocks.