Scientists have found a new way to measure the age of the universe — by counting the birthdays of ancient stars in our own galaxy. A team led by astronomer Indranil Banik from the University of Portsmouth studied more than 155,000 stars in the Milky Way to independently calculate how old everything is. Their answer? The universe is about 13.8 billion years old, which matches what scientists have believed for decades.
The finding is good news for the "standard model" of cosmology, the broadly accepted framework that describes how the universe began and evolved. The research, posted online in July, adds another line of evidence supporting this picture.
Banik and his colleagues looked at a special type of star called a subgiant — stars that are transitioning from their main life phase into a later stage. These stars act like cosmic timekeepers. "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 wrote.
Think of it like archaeology. If you dig up a fossil that's 100 million years old, you know the rock layer beneath it must be even older. Similarly, if astronomers find a star that's 13 billion years old, the universe must be at least that old — plus some extra time for that star to form after the Big Bang.
The researchers started with 247,103 subgiant stars from two major sky surveys: LAMOST and Gaia. After filtering out stars that didn't fit the chemical patterns of ancient stars, they were left with 155,600 stars to analyze. The oldest star they found was about 13.73 billion years old, with an uncertainty of roughly plus or minus 0.2 billion years. Adding the roughly 200 million years it would have taken for that star to form after the Big Bang brings the total to about 13.8 billion years.
This matters because of something called the Hubble tension — a puzzle in astronomy. There are two main ways to measure how fast the universe is expanding. One uses the afterglow of the Big Bang, called the cosmic microwave background, and suggests the universe is 13.8 billion years old. The other uses nearby stars and explosions, and gives a noticeably higher expansion rate, which would make the universe younger — only 12.5 to 12.9 billion years. The two methods disagree by about 9%.
This new star census favors the older age. It suggests the Hubble tension is probably caused by something relatively recent and local — like a giant cosmic void making our neighborhood expand faster than average — rather than new physics affecting the entire history of the universe. "Taken together, these results suggest a late universe solution to the Hubble tension," the researchers explained.
The team acknowledges five sources of uncertainty that could still affect their result, but say no single fix would dramatically change the picture. For now, the evidence points toward a universe that is ancient, consistent, and behaving according to rules we can understand.