An Ancient Cluster Hidden in the Glare of Sagittarius

A faint ball of stars buried behind thick dust near the center of the Milky Way may be one of the oldest objects in our galaxy. Astronomers estimate that the globular cluster VVV CL001 is about 13.4 billion years old, give or take 400 million years, according to a study accepted for publication and reported by Phys.org on Nov. 2.

That figure would place the cluster's birth only a few hundred million years after the Big Bang, which happened about 13.8 billion years ago. If it holds up, VVV CL001 would be a near-pristine sample of the material the Milky Way was built from — a fossil from the galaxy's infancy.

The age is an estimate, not a settled measurement. It depends on stellar models and, above all, on how far away the cluster is. Those two inputs are hard to pin down for an object this deeply buried.

Globular clusters are tightly packed swarms of hundreds of thousands of stars. Astronomers often call them galactic fossils because their stars formed early and have changed little since. NASA's Jet Propulsion Laboratory has described them as among the oldest objects in our galaxy, with ages of roughly 10 to 13 billion years.

The Milky Way hosts at least 170 known globular clusters. Most of the well-studied ones orbit in the galaxy's outer halo, far from the dust that fills the central bulge. VVV CL001 sits in the constellation Sagittarius, close to the galactic center, roughly 24,000 light-years from Earth.

Seeing Through the Dust With Infrared Light

The galactic bulge is one of the hardest places in the sky to study. Thick clouds of interstellar dust block and redden visible light. Millions of unrelated foreground and background stars crowd every image, so it is hard to tell which stars actually belong to a cluster.

Infrared light gets around much of the problem — its longer wavelengths pass through dust that scatters visible light, which is why near-infrared surveys have uncovered many hidden clusters. One of those surveys, VISTA Variables in the Vía Láctea (VVV), run from Chile, has used infrared imaging to reveal previously hidden open and globular clusters across the inner galaxy. VVV CL001 was the first globular cluster that the survey found in 2011.

For the new study, a team led by Julio Olivares Carvajal used near-infrared images from the FourStar camera on the 6.5-meter Magellan Baade Telescope in Chile. Those images span about 13 years. Because cluster stars move across the sky together, the team could sort true members from unrelated stars by their shared motion.

Hubble Space Telescope images, which are less affected by dust, then let the researchers examine the cluster's main-sequence turnoff. That is the point where a cluster's stars begin to exhaust their core hydrogen, and it works as one of astronomy's most dependable age markers.

"Both methods estimate the cluster age at 13.4±0.4 Gyr," the team wrote, according to Phys.org, using the astronomers' shorthand for billion years. The researchers added that the result makes VVV CL001 a candidate for the oldest globular cluster in the bulge, and possibly in the entire galaxy.

An Age That Depends on the Distance

Readers should treat the 13.4-billion-year figure as model-dependent. Cluster ages come from comparing observed stars with computer models of how stars of a given mass and chemistry evolve. Those models agree well with one another, but they share many of the same assumptions.

Distance matters even more. A star that looks faint could be dim and nearby, or bright and far away. A detailed summary of the paper by Martin Cid Magazine reports that the team estimates a systematic uncertainty of about 1 billion years tied to distance, on top of the stated 400-million-year range. Using a slightly smaller distance from an earlier study would push the age to about 13.7 billion years, uncomfortably close to the age of the universe itself.

Earlier estimates came out younger. A 2021 analysis of the cluster's chemistry estimated a median age of about 11.9 billion years, and a separate 2025 study arrived at about 12.1 billion years. Both relied on images that did not reach the turnoff stars as clearly. The new Hubble data reach that turnoff for the first time, but not the entire turnoff region, and only two horizontal-branch stars could be used to anchor the distance.

The study type matters too. This is an observational analysis that has been accepted by a journal but not yet independently repeated. No outside team has confirmed the 13.4-billion-year age. The researchers plan high-resolution spectroscopic follow-up to check the cluster's chemistry.

Clues to the Galaxy's Earliest Building Blocks

The cluster's chemistry is part of what makes it special. Its stars carry only about 0.6% of the Sun's proportion of iron relative to hydrogen. That makes VVV CL001 the most metal-poor globular cluster known in the bulge, suggesting it formed from gas that had barely been enriched by earlier generations of stars.

Its orbit adds another clue. The cluster's path stays confined to the inner galaxy, which suggests it formed in place rather than being captured from a passing dwarf galaxy. Phys.org reports that the cluster may represent an ancient stellar population that formed where it sits today.

The 2025 study reached a similar view. Its authors concluded that "VVV-CL001 would be a fossil remnant from the earliest phases of Galactic assembly." If that reading is right, the cluster is a direct sample of the Milky Way's original core rather than a later addition.

VVV CL001 also has company. Other bulge clusters, including Ton 2, NGC 6558 and HP 1, have recently been dated between about 12.9 and 13.6 billion years. Rather than standing clearly apart, VVV CL001 appears to belong to a tight group of very old clusters near the galactic center.

For astronomers, that grouping is the bigger story. It suggests the Milky Way's central bulge began forming stars remarkably early. Confirming that picture will require better distances, deeper infrared imaging and detailed chemical measurements, work that future telescopes are well positioned to do.

For everyday stargazers, VVV CL001 is far too faint and dust-hidden to see. But the Sagittarius region it lies in is visible low in the southern sky from much of the U.S. in summer. That patch of sky marks the direction of the galaxy's oldest known neighborhoods.

What Readers Want to Know

What is VVV CL001? It is a globular cluster, a dense group of hundreds of thousands of stars, located in the Milky Way's central bulge in the constellation Sagittarius, about 24,000 light-years from Earth.

How old is the cluster? The study estimates about 13.4 billion years, plus or minus 400 million years. Researchers add a further uncertainty of roughly 1 billion years tied to the cluster's distance.

Is it confirmed as the oldest cluster in the Milky Way? No. The team calls it a strong candidate. Other bulge clusters have similar estimated ages, and no independent group has repeated the measurement yet.

Why are bulge clusters so hard to study? Thick dust dims and reddens their light, and crowded star fields make it hard to separate cluster members from unrelated stars. Infrared imaging and long-term tracking of star motions help solve both problems.

Why does the cluster matter for understanding the galaxy? Its extremely low metal content and inner-galaxy orbit suggest it formed early and in place, making it a possible fossil of the Milky Way's original core.

What happens next? Researchers plan high-resolution spectroscopy to check the cluster's chemical makeup. Better distance measurements would also sharpen the age estimate.