'Birth certificate' of oldest known star found

Astronomers using NASA's Hubble Space Telescope say they are a step closer to finding the exact birth date of the oldest star known yet.
"We have found that this is the oldest known star with a well-determined age," said Howard Bond of Pennsylvania State University.
The star could be as old as 14.5 billion years (plus or minus 0.8 billion years), which at first glance would make it older than the universe's calculated age of about 13.8 billion years, an obvious dilemma, NASA said.
But earlier estimates from observations dating back to 2000 placed the star as old as 16 billion years. And this age range presented a potential dilemma for cosmologists.

"Maybe the cosmology is wrong, stellar physics is wrong, or the star's distance is wrong. So we set out to refine the distance," Bond said in a statement.
The new Hubble age estimates reduce the range of measurement uncertainty, so that the star's age overlaps with the universe's age - as independently determined by the rate of expansion of space, an analysis of the microwave background from the big bang, and measurements of radioactive decay.

The "Methuselah star," catalogued as HD 140283, has been known about for more than a century because of its fast motion across the sky.
The star formed at a very early time before the universe was largely "polluted" with heavier elements forged inside stars through nucleosynthesis, researchers said.

Hubble's observational prowess was used to refine the distance to the star, which comes out to be 190.1 light-years.
Before the Hubble observation, the European Space Agency's Hipparcos satellite made a precise measurement of the star's parallax, but with an age measurement uncertainty of 2 billion years.
Bond's team managed to shrink the uncertainty so that the age estimate was five times more precise.
The star has a higher than predicted oxygen-to-iron ratio, and this too lowers the age. Bond thinks that further oxygen measurement could reduce the star's age even more, because the star would have formed at a slightly later time when the universe was richer in oxygen abundance.

Lowering the upper age limit would make the star unequivocally younger than the universe.
"Put all of those ingredients together and you get an age of 14.5 billion years, with a residual uncertainty that makes the star's age compatible with the age of the universe," said Bond.
The study published in the Astrophysical Journal Letters.