Astronomers have used the ages of more than 155,000 stars in the Milky Way to independently estimate the age of the universe, and their findings may be good news for the standard cosmological model. The new research was reported in a paper submitted to the arXiv preprint server on July 1.
Age tracers
The age of the universe is tied to a discrepancy known as the Hubble tension. There are two main ways to measure how fast the universe is expanding, known as the Hubble constant. The first uses the cosmic microwave background (CMB), the “afterglow” of the Big Bang, and gives a certain value. The other uses local measurements in our cosmic neighborhood, including Cepheid stars and supernovae, and gives a noticeably higher value.
The two figures disagree by about 9%—a mismatch known as the Hubble tension.
The universe’s actual age depends on these figures: if standard cosmology (ΛCDM) with the CMB-based figure is correct, the universe is about 13.8 billion years old. If the locally measured expansion rate applies throughout almost all of cosmic history, calculations suggest the universe would be only about 12.5–12.9 billion years old. Astronomers have proposed a range of explanations for the Hubble tension. Some point to new physics that shaped the universe’s expansion from its earliest moments; others suggest the mismatch is a more recent or local effect.
Cosmic fossils
In this new study, a team led by Indranil Banik of the University of Portsmouth independently calculated the minimum age of the universe using the oldest stars in the Milky Way galaxy. Just as tree rings or fossils tell geologists about Earth’s past, old stars act as “fossils” for the universe.
“We can also achieve this by studying the oldest Galactic stars, which serve as ancient ‘fossils’ telling us about the history of the universe,” the team writes in the paper. If astronomers find a star that’s 13 billion years old, then the universe must be at least that old plus a bit more, since stars would have taken some time after the Big Bang to form.
The researchers began with 247,103 “subgiant” stars—stars just past the main-sequence phase of their lives—whose ages are easier to measure accurately. The stars came from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and Gaia surveys. The researchers cleaned the sample to remove stars that didn’t fit the chemical pattern of typical old stars. They were left with a sample of 155,600 stars after a cross-check with another independent method.
By analyzing these oldest long-lived stars in the Milky Way galaxy, the team found that the oldest star is about 13.73 billion years old (with a small uncertainty of roughly +0.18/-0.15 billion years). This figure is more consistent with prior studies using other old stars and globular clusters and with the standard cosmological prediction from the CMB, assuming it would have taken about 200 million years (0.2 billion years) for that star to form after the Big Bang.
A recent effect
The team cautions that five sources of uncertainty could still introduce errors in the results. They are sample size, quality cuts, stellar model assumptions, star-formation timescales and theoretical predictions. Each limits precision by about 0.15–0.2 Gyr, meaning no single improvement would sharply refine the result.
Nevertheless, the estimated age is notably higher than the figure expected if the Hubble tension arose from new physics affecting nearly all of cosmic history. Instead, it favors solutions in which whatever’s causing the Hubble tension is a more recent, “late-time” phenomenon.
Researchers say this could indicate a change in how the universe has expanded only in the past several billion years, or other local effects, such as the presence of a void that makes local expansion appear artificially fast. “Taken together, these results suggest a late universe solution to the Hubble tension,” they explain. “Another possibility is that the Hubble tension is due to a large local underdensity or void.”
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Publication details
Indranil Banik et al, The age of the Universe from a large sample of the oldest Galactic stars, arXiv (2026). DOI: 10.48550/arxiv.2607.00764
Journal information:
arXiv
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A new stellar census strengthens the case for a 13.8-billion-year-old universe (2026, July 15)
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