Our oldest stellar neighbor now has something of a near-official birth certificate, thanks to the Hubble Space Telescope.
The “Methuselah star,” also known as HD 140283, lies about 190 light years away from Earth in the constellation Libra. Astronomers have been studying the star for more than a century, but it wasn’t until very recently that anyone tried to calculate its age. Scientists knew, however, that it was likely a very old star, since it contains very few heavy elements, meaning it formed in the very early universe, before other stars began forging the first metals.
“We believe this star is the oldest known in the Universe with a well determined age,” Pennsylvania State University astronomer Howard Bond told Nature in January.
Some initial age estimates using observations stretching back to the year 2000 pegged Methuselah as truly ancient – 16 billion years old. However, that’s a dubious estimation since according to the best data we have, the universe is only 13.8 million years old!
Now, newly refined observations have rounded the initial Methuselah figure down to 14.5 billion years, plus or minus 800 million years -- which, at the younger end of that range, is actually feasible given what we know about the Big Bang. Researchers led by Bond published their latest findings in Astrophysical Journal Letters on March 1.
The new age estimate comes from new Hubble observations that pinned Methuselah’s distance from Earth more precisely than previous estimates from the European Space Agency’s Hipparcos satellite. Knowing the distance allowed Bond and his team to better calculate Methuselah’s intrinsic brightness, which then allowed the team to better scrutinize the star’s chemical makeup and structure.
They found that Methuselah has a much higher oxygen-to-iron ratio than previously thought, lowering the age estimate even more. The universe got more oxygen-rich as it aged, so more oxygen means a younger star.
"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. "This is the best star in the sky to do precision age calculations by virtue of its closeness and brightness."
Methuselah likely started off as a resident of a primeval dwarf galaxy that was then gobbled up by the Milky Way 12 billion years ago. Being sucked into our galaxy left Methuselah with an elongated orbit, zooming through our solar neighborhood at around 800,000 miles per hour.