Hubble Reveals Complex History of NGC 6723

A new image from the Hubble Space Telescope of the globular cluster NGC 6723, released on June 26, 2026, reveals a complex stellar population. The cluster, located 27,000 light-years away in the constellation Sagittarius, contains tens of thousands to possibly millions of stars.

NGC 6723 is one of roughly 150 known globular clusters orbiting in the Milky Way's halo. These clusters are among the most ancient structures in our galaxy, with stars often older than 10 billion years. Some stars date back nearly to the universe's beginning 13.8 billion years ago. They likely formed billions of years before the galaxy's thin disk, where our sun resides, took shape.

Challenging Old Theories

The traditional view held that all stars in a globular cluster formed simultaneously from the same material. This would mean the stars share identical ages and chemical compositions. Hubble's view of the Chandelier Cluster, as it is also known, demonstrates this is not the case.

The image shows a dense concentration of bright-blue stars at the cluster's center, with more orange stars toward the edges. Since blue stars are younger than orange stars, this suggests the cluster has a complex history with multiple stellar populations.

Hubble's Detailed Surveys

Hubble first studied NGC 6723 in visible and near-infrared light in 2013 as part of a major survey of 65 globular clusters. That research found that massive stars sink toward a cluster's center while lower-mass stars drift outward. Further studies in 2013 and 2014 searched for small chemical differences and measured the spread of stellar ages within NGC 6723.

Those observations identified two distinct epochs of star formation. The data indicates a second burst of star formation occurred approximately 634 million years after the first.

Origins and Galactic Context

One leading hypothesis is that globular clusters formed from the rapid collapse of enormous gas clouds in the early universe. However, recent simulations suggest an alternative: some clusters may be the surviving cores of ancient dwarf galaxies stripped of their outer stars by larger galaxies. Either way, they act as fossil remnants offering clues to galactic evolution.

Globular clusters are not exclusive to the Milky Way. They are found around many galaxy types, including spirals, giant ellipticals, and dwarfs. According to NASA, the nearby Andromeda galaxy is estimated to host about 460 globular clusters. The giant elliptical galaxy M87 contains roughly 15,000.