MORE than a century after it was first observed by astronomers a star has been identified as the oldest yet seen in the universe.

The star is just 186 light years away from Earth and is at least 13.2 billion years old, and quite possibly many millions of years older than that.

The Big Bang is calculated by scientists to have taken place about 13.77 billion years ago and the star, known only as HD 140283, was among the earliest stars to form. ‘We believe this star is the oldest known in the Universe with a well determined age,’ Howard Bond, an astronomer at Pennsylvania State University, told the American Astronomical Society.

Because it contains some heavy elements it is thought to have been one of the second generation of stars to be created following the Big Bang.

The first generation of stars contained hardly any elements heavier than helium but when they exploded in a succession of supernovas within a few hundred million years after forming they were replaced by stars like HD 140283.

Observations from the Hubble Telescope helped researchers fix the distance of the star from the Earth with unprecedented accuracy which allowed them to make more accurate measurements of how brightly it shines.

Once its brightness was established they were able to work out how rapidly its hydrogen is being exhausted and so determine its age.

When stars start running short of hydrogen they start dimming which is regarded as a reliable indicator of age.

The actual age that the astronomers’ calculations gave was 13.9 billion years but calculations of this type usually contain large error margins.

In the case of HD 140283 the error margin was 700 million years, making it at least 13.2 billion years old. One other star, known as Methuselah2, has previously been shown to be 13.2 billion years old but the research team are confident they have determined HD 140283’s age with greater certainty.                –MO