What is the oldest known star in the universe?

But it wouldn’t take much to refute this idea. If we were to find a star definitively older than this one, it would show that the universe existed before 13.8 billion years ago. Enter star HD 140283, which appears suspiciously non-metallic.

HD 140283, better known as the star Methuselah, is located about 200 light years from Earth in the constellation Libra. It is known to be a high-speed subgiant star and one of the closest metal-poor stars to our solar system.

“The high speed of movement proves that the star is simply a visitor to our stellar neighborhood,” NASA’s Hubble mission team explains about the star. “Its orbit carries it across the plane of our galaxy from the ancient halo of stars surrounding the Milky Way, and will eventually return to the galactic halo.”

In the 1950s, astronomers discovered that HD 140283 was very metal-poor compared to other nearby stars, suggesting that the star formed earlier in the universe, before being “polluted” by heavier elements merging into the centers of other stars. In the early 2000s, astronomers tried to evaluate it and arrived at an even more surprising result. According to their observations and analyzes using stellar evolution models, the age of the star Methuselah was probably around 16 billion years.

The ages of stars are quite difficult to pin down, relying on measurements of their absolute luminosity as well as their chemical abundances, and it is far from being the last word on the subject.

“Maybe the cosmology is wrong, the stellar physics is wrong, or the distance to the star is wrong,” Howard Bond of Pennsylvania State University in University Park and the Space Telescope Science Institute in Baltimore said in a 2013 statement, after new measurements by the Hubble Space Telescope. “So we decided to refine the distance.”

This team refined the distance measurements to the star, an important step in determining the intrinsic luminosity of a star, fundamental to determining its age. Think of it like you don’t know whether you see a torch held by an approaching stranger or a lighthouse far away. Placing the star’s distance at 190.1 light years and finding that it had a higher oxygen-to-iron ratio than expected, the team aged the star to be a much less revolutionary star in the model of the universe.

“Put all these ingredients together and you get an age of 14.5 billion years, with a residual uncertainty that makes the age of the star consistent with the age of the universe,” Bond said, adding: “It is the best star in the sky for making precise age calculations because of its proximity and brightness.”

With an uncertainty of about 0.8 billion years, at the lower end of the age estimate, it is at least not older than the universe is thought to be. Other studies have placed the star’s age between 13.7 and 12.2 billion years, with another suggesting between 11.5 and 12.5 billion years.

The star Methuselah, named after Noah’s biblical grandfather, described as dying at the age of 969, is probably not older than the universe, nor does it prove that we are horribly wrong about the age of the universe. But it remains the oldest star we have found so far in the universe. There are other candidates, such as J22132050-5137385, which is believed to be around 13.6 billion years old, give or take 2.6 billion years. Further measurements of this and other stars could cause Methuselah to lose the top spot, or could refine the age estimate downward.