Old stars act as cosmic fossils to date our universe
In short: How do we know how old the universe is? While light from the Big Bang provides one answer, a new method looks at the Milky Way's oldest inhabitants. By treating ancient stars like tree rings, astronomers are finding evidence that supports our current understanding of cosmic history.
The age of the universe is currently tied to a significant discrepancy known as the Hubble tension. This refers to the disagreement between two primary methods of measuring the expansion rate of the universe (the Hubble constant). One method relies on the cosmic microwave background—the afterglow of the Big Bang—while the other uses local measurements from nearby objects like Cepheid stars and supernovae. These two figures currently disagree by about 9%.
The stakes for this measurement are high: if the expansion rate derived from the cosmic microwave background is correct, the universe is approximately 13.8 billion years old. Yet, assuming that cosmic expansion rates remained constant across most history, figures indicate a significantly younger cosmos of roughly 12.5–12.9 billion years. This mismatch has led some scientists to propose that new physics may have shaped the universe's expansion in its earliest moments.
Seeking a solution, University of Portsmouth researchers headed by Indranil Banik performed an autonomous analysis involving upwards of 155,000 Milky Way stars. By identifying and dating 'subgiant' stars—which are easier to measure accurately than other types—the researchers established a minimum age for the universe. Because stars require time to form after the Big Bang, finding a star that is 13 billion years old proves the universe must be at least that old plus additional time. This stellar census provides a crucial independent check on our cosmological models.
The study highlights a shift toward using 'cosmic fossils.' Just as geologists use tree rings or physical fossils to reconstruct Earth's history, astronomers are now using the oldest Galactic stars to verify the timeline of the cosmos. By anchoring the universe's age in tangible stellar data, researchers can better determine whether the Hubble tension is a local anomaly or a sign of fundamental new physics.
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Sources
- Summary by Intellect · source: New Method Finally Confirms the Age of the Universe
- Also: A new stellar census strengthens the case for a 13.8-billion-year-old universe
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