Close-up: Globular Star Cluster NGC 6723 in Sagittarius | Hubble Space Telescope

Close-up: Globular Star Cluster NGC 6723 in Sagittarius | Hubble Space Telescope

This Hubble Space Telescope picture is of an ancient inhabitant of our galaxy. This sparkling scene is of a globular cluster: a collection of tens of thousands to millions of stars, all tightly bound together under the influence of gravity. Astronomers know of more than 150 globular clusters in our galaxy, though there may be others yet to be discovered, hidden from view by dust or densely packed fields of stars.

This particular globular cluster is NGC 6723, sometimes called the Chandelier Cluster. Much like its namesake, this cluster sparkles with countless lights—but each ‘lightbulb’ in this chandelier is an individual star 27,000 light-years away in the constellation Sagittarius (the Archer).

Globular clusters like NGC 6723 contain examples of the oldest stars in our galaxy. The ages of these clusters often exceed 10 billion years old, and can be nearly as old as the Universe itself. Globular clusters are thought to be among the first structures to have formed in our galaxy, coalescing potentially billions of years before the thin disk of stars where our Sun orbits. The details of how globular clusters formed, however, are not yet certain. In NGC 6723, researchers found evidence of two closely-spaced periods of star formation, the second occurring within 634 million years of the first. This is a "blink of an eye" for a star cluster that is more than 10 billion years old.

Astronomers initially thought that all stars in a globular cluster formed at the same time in a single flourish of star formation. This would mean that all stars in a globular cluster would be the same age and be made of the same mixture of chemical elements. Now, thanks to observations from telescopes like Hubble, researchers know that these seemingly simple stellar populations have more complex histories than originally thought.

Hubble first observed NGC 6723 as part of an ambitious survey dedicated to demystifying the properties of globular clusters in our Milky Way galaxy. In this observing program (#10775, PI: Sarajedini), researchers used Hubble to study 65 globular clusters in our galaxy in visible and near-infrared light. These data allowed researchers to study everything from the ages of globular clusters to the process of massive stars sinking towards the center of a star cluster and of lower-mass stars drifting toward cluster outskirts. This survey has been scientifically valuable and has supported several hundred published research papers.

In a later observing program (#13297, PI: Piotto), researchers set their sights again on many of these same clusters, including NGC 6723. This time, they used Hubble’s unique sensitivity to ultraviolet light to detect the subtle variations in chemical composition between the stars of globular clusters and determine the age spread among the clusters’ stars. 

Thanks to these findings, astronomers are on the path to understanding how and when globular clusters formed—and Hubble observations of celestial chandeliers like NGC 6723 are lighting the way.

Image Description: A globular cluster. It is made up of many thousands of bright stars, tightly-packed in the center and more spread out at the corners, but filling the entire view. The stars are colored either orange or bright blue with the blue stars mainly concentrated in the center. Orange stars are located mainly around the edge, and also vary in size from small dots to glowing stars with four points, based on their position in the foreground or background of the cluster.

Credit: European Space Agency/Hubble & NASA, A. Sarajedini, G. Piotto

Duration: 30 seconds
Release Date: June 26, 2026

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