Near the center of the Milky Way, behind dense clouds of interstellar dust, lies a globular cluster almost as old as the Universe itself. For the first time, astronomers have identified stars within it that allowed them to measure its distance and age. Its orbit lies entirely within the Galaxy’s central region. Most likely, the cluster formed within the Milky Way rather than arriving from elsewhere, and it may prove to be the oldest in our Galaxy.
Almost as Old as the Universe
VVV CL001 is approximately 13.4 billion years old, with a statistical uncertainty of 400 million years in either direction. Current estimates place the age of the Universe at 13.8 billion years. The cluster is almost three times older than the Sun, which is about 4.6 billion years old.
Globular clusters are among the oldest objects in the Galaxy. The age of the oldest cluster therefore sets a minimum age for both the Galaxy and the Universe. For VVV CL001, this estimate nearly matches the age of the Universe determined using other methods.
The authors acknowledge that uncertainty in the distance adds approximately another billion years to the age uncertainty. Using the distance estimate of about 23,000 light-years from a study published in Astronomy & Astrophysics in early 2026 gives the cluster an age of 13.7 billion years—almost as old as the Universe.
Hidden Behind Dust
The cluster was discovered in 2010 during the VISTA Variables in the Vía Láctea infrared sky survey, but its nature was not confirmed until 2019. Interstellar dust dims its visible light by a factor of approximately 5,000, so the object has so far been studied almost exclusively at infrared wavelengths.
The cluster is also small and faint, and no RR Lyrae variable stars—the usual tools for measuring distances—have been found within it. As a result, its distance was known with an uncertainty of at least 3,000 light-years. That distance, in turn, affected calculations of its orbit around the Galactic center. It is approaching us at 325 kilometers per second, while the surrounding stars move very differently. Depending on the assumed distance, calculations showed the cluster either remaining within the central region or traveling beyond it.
How Its Age Was Measured
The stars in a globular cluster formed at nearly the same time, but more massive stars evolve faster. When the hydrogen in a star’s core runs out, it leaves the main sequence—the stage of stable nuclear fusion. The location where this happens on a stellar diagram is called the turnoff point.
The older the cluster, the less massive and fainter the stars that have already reached the turnoff point, so its position on the diagram reveals the cluster’s age. Meanwhile, horizontal-branch stars are already converting helium into carbon in their cores. They all shine with nearly the same intrinsic brightness, allowing their apparent brightness to be used to determine distance.
Julio Olivares Carvajal’s team at the Capodimonte Astronomical Observatory used infrared images from the Magellan Baade telescope in Chile and the Hubble Space Telescope. They distinguished genuine cluster members from unrelated stars through their shared motion across the sky, comparing images taken almost 13 years apart with the help of a machine-learning algorithm. This identified 155 stars, including, for the first time, both stars at the turnoff point and horizontal-branch stars.
The resulting distance was approximately 24,000 light-years, with an uncertainty of about 1,500 light-years—greater precision than anyone had previously achieved. The paper has been accepted for publication in the peer-reviewed journal Astronomy & Astrophysics, and its preprint is available on arXiv.
Born in the Galactic Center
According to its refined orbit, the cluster never travels more than 7,000 light-years from the Galactic center. Its stars contain approximately 160 times less iron than the Sun. Generally, the fewer elements heavier than helium a cluster contains, the earlier it formed. All of this indicates that VVV CL001 most likely originated in the Galaxy’s central region rather than arriving in a dwarf galaxy that was later absorbed. As Phys.org reports, if this is indeed the case and the cluster is that old, the age of the Galaxy—and possibly the Universe—will need to be reconsidered.
The team plans to verify the cluster’s origins using high-resolution spectroscopy, which will reveal the abundances of different chemical elements in its stars. New optical observations should also capture fainter horizontal-branch stars that are not visible in the current images.
