Astronomers Find Oldest Star Yet

Larry O'Hanlon, Discovery News

May 14, 2007 — A stellar Methuselah nearly as old as the universe has been identified right here in the Milky Way Galaxy.

Known as HE1523-0901, the 13.2-billion-year-old star was born half a billion years after the universe exploded into existence, say astronomers.

That unprecedented birthdate was confirmed by using the European Southern Observatory's (ESO) Very Large Telescope to split the star's ultraviolet light into individual wavelengths — like a UV rainbow. In that rainbow, or spectrum, they were able to identify lines that show the presence of heavy elements like uranium and thorium.

"We see gold and silver in these stars," added astronomer Anna Frebel of the McDonald Observatory in Texas. Frebel is lead author of a paper about the discovery in the May 10 issue of Astrophysical Journal.

Heavy elements decay into lighter elements over vast but reliable amounts of time. That process serves as an atomic clock to measure how long minerals or in this case, a star, have been around.

Unlike other potentially old stars out there, HE1523-0901 just happens to have been born in a corner of the galaxy that was heavily polluted with heavy elements.

"They have basically six different clocks," said ESO astronomer Wolfram Freudling. "It's really a breakthrough."

Past attempts to measure the ages of apparently old stars were based on just one elemental clock, said Freudling, which made it impossible to cross-check for accuracy. But with a half-dozen nuclear clocks there is very little doubt that HE1523-0901 is the oldest star on the books.

"It's a normal, old, primitive star that formed with this baggage," Frebel told Discovery News.

And those heavy elements have yet another tale to tell, said Frebel. They are very likely the remains of an even earlier, short-lived super giant star, which manufactured the elements in the extreme atom-fusing pressures of its death throes.

"So this may be the first or second generation of stars," Frebel said of the long-gone super giant.

So in a way, HE1523-0901 is the lucky exception to a cosmic Catch-22: The oldest stars are expected to have the least heavy elements and harder to date because there were few stars around before them to churn those elements out. What's absolutely certain is that HE1523-0901 itself could not have produced the heavy elements itself.

Like all old stars, HE1523-0901 is quite small and stable, and very unspectacular in appearance. And like all old stars, its size is somewhere between 20 and 30 percent smaller than the sun.

"These (small old stars) are very quiet survivors," Frebel said.

Source: Discovery Channel