Home Science Space Astronomers discover HE 1523 star: Almost as old as universe


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HE 1523-0901 is a star within our Milky Way galaxy that astronomers estimate to be about 13.3 billion years old. It is the oldest object yet discovered in our galaxy. HE 1523 is only about 400 million years younger than the age of the universe itself (estimated at 13.7 billion years).

A team of astronomers, which includes Anna Frebel (Research School of Astronomy and Astrophysics, Australian National University), found that HE 1523-0901 contains only a few elements heavier than hydrogen and helium. Two of these heavier elements are uranium (U) and thorium (Th). With these two elements, the researchers measured the age of HE 1523-0901 based on the radioactive decay of uranium (U) and thorium (Th), two radioactive elements.

The process of using radioactive decay measures a radioactive element’s half-life, which is the amount of time it takes for 50% of the original amount to decay. Uranium and thorium have half-lives of 4.7 billion and 14 billion years, respectively.

HE 1523-0901 is a bright red giant star within a group of bright metal-poor stars observed from the Hamburg/ESO Survey (European Southern Observatory’s Very Large Telescope [VLT]). It can be seen with a telescope from the Southern Hemisphere. The star is about 80% the size of the Sun.

The scientists studying HE 1523-0901 contend that the star was formed directly from scattered materials left over after first generation stars—with sizes about 200 times that of our Sun—exploded at the end of their lives (which lasted probably only for a few hundred million years).

(First generation stars are the group of stars that formed first after the Big Bang, the theorized beginning of our universe. They are considered by astronomers to have formed between 30 and 150 million years after the Big Bang.)

Frebel’s team state that uranium and thorium found within HE 1523-0901, which they used to estimate its age, were probably left over from first generation stars that exploded as supernovas.

The article bearing this information is found in the May 10, 2007 issue (volume 660, part 2 (2007), pages L117–L120) of Astrophysical Journal. The article is titled “Discovery of HE 1523-0901, a Strongly r-Process enhanced Metal-poor Star with Detected Uranium”. Authors of the article include Anna Frebel, Norbert Christlieb, John E. Norris, Christopher Thom, Timothy C. Beers, and Jaehyon Rhee.


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