HD 140283, nicknamed the Methuselah star, once appeared older than the universe in a widely reported age estimate. It is not evidence of a star predating the Big Bang: the estimate carries enough uncertainty to overlap the universe’s age, and it depends on how astronomers model the star’s chemical makeup and evolution.
What is the Methuselah star?
HD 140283 is a nearby, fast-moving, extremely metal-poor subgiant in the constellation Libra. NASA gives its distance as 190.1 light-years, or 58.3 parsecs, and lists its coordinates as right ascension 15h 43m 03s.10 and declination −10° 56′ 00″.60. NASA’s Hubble release reports that its heavy-element content is about 1/250 that of the Sun.
That scarcity of heavy elements is a clue to its history. Much of the material heavier than hydrogen and helium is made in stars and dispersed into space; a star with very little of it likely formed before many generations of stars had enriched the surrounding gas. HD 140283’s elongated, halo-like orbit is consistent with an ancient stellar population and may reflect the Milky Way’s accretion of a dwarf galaxy.
Why did it seem older than the universe?
A 2013 study estimated the star’s age at 14.46 ± 0.31 billion years using its measured parallax and adopted chemical abundances. That is a parallax-only uncertainty, not the full error budget. When uncertainties in stellar parameters and composition were included, the uncertainty grew to about ±0.8 billion years. NASA and ESA reported the result as 14.5 ± 0.8 billion years.
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The comparison in that paper was a universe age of 13.77 ± 0.06 billion years, based on the cosmic microwave background and the Hubble constant. The central value for HD 140283 is higher, but the star’s estimated one-standard-deviation range extends down to about 13.7 billion years. The two estimates therefore overlap; the apparent age problem is not a demonstrated contradiction.
How astronomers estimated the star’s age
Stars do not come with birth dates. Astronomers infer age by comparing observed properties with stellar-evolution models: as a star changes over time, its brightness, temperature, and position in an evolutionary stage such as the subgiant phase change in ways the models can predict.
The 2013 analysis used a Hubble Fine Guidance Sensor trigonometric parallax of 17.15 ± 0.14 milliarcseconds to improve the star’s distance estimate. It then compared the observations with modern stellar isochrones, accounting for helium diffusion, revised nuclear reaction rates, and enhanced oxygen abundance. For adopted [O/H] = −1.67 and [Fe/H] = −2.40, the resulting parallax-only age was 14.46 ± 0.31 billion years. The broader estimate of about 14.5 ± 0.8 billion years includes additional uncertainties in the stellar parameters and chemical composition.
What makes the age uncertain?
- Distance: Parallax determines distance, which in turn affects the star’s inferred brightness. The Hubble measurement reduced the distance uncertainty compared with earlier Hipparcos data, but did not remove other sources of error.
- Chemical abundances: Oxygen and iron affect how a star evolves and therefore the age inferred from its observed properties. The 2013 paper found that, after the improved parallax, composition contributed more to the error budget than distance.
- Stellar physics: Choices about helium diffusion, nuclear reaction rates, convection, and the adopted mix of elements alter the model tracks used to estimate age.
- Abundance-specific modeling: A 2024 study using a tailored abundance mixture for HD 140283 reports materially different ages from different mixture assumptions. A solar-scaled mixture can yield an age of about 14 billion years, illustrating why no single headline value should be treated as exact.
So, is HD 140283 really older than the universe?
No such conclusion is established by the famous estimate. The accurate description is that its central 2013 age estimate was higher than the universe-age value used in the comparison, while the substantial uncertainty ranges overlap. The result points to a star that likely formed very early in cosmic history, not one shown to have existed before the universe.
Age estimates can change as measurements of the star’s properties and the models used to interpret them improve. The 2013 result remains important because it made the uncertainty visible: the inferred age depends on distance, chemical abundances, and stellar physics, not just on a number read directly from the star.
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