A star near our solar system is the oldest ever detected - it formed shortly after the Big Bang, and could throw light on what happened in the earliest years of the universe.
The star, HD 140283 is 13.2 billion years old, and could be much older. It lies 190 light years from Earth, and has been studied by astronomers for over a century.
The universe formed 13.77 billion years ago, and the new find hints that generations of stars lit up very soon after that.
The report, published in the journal Nature, offers insight into what happened after the Big Bang.
“We believe this star is the oldest known in the Universe with a well determined age,” says Howard Bond, an astronomer at Pennsylvania State University in University Park in an article published in Nature.
The star consists almost entirely of hydrogen and helium - a sign of having formed early in the history of the Universe.
Measurements using the Hubble space telescope exploited the fact that the star is slowly dimming as it burns up the hydrogen in its core - a reliable way to calculate its age.
The Pennsylvania team's calculations showed the star is 13.9 billion years old, plus or minus 700 million years - so it is at least 13.2 billion years old, and may well be older.
The star is part of the second generation of stars: the first were made purely of hydrogen and helium, and exploded in supernovae after a few million years.
The explosions heated gas and seeded it with heavier elements, traces of which can be seen in HD 140283.
Volker Bromm, an astronomer at the University of Texas at Austin says that this means the mechanism to form the second generation of stars “must have been in place very early”.