The Oldest Stars in the Universe
The oldest star so far, is HE 1523-0901. HE 1523-0901 is the designation given to a red giant star located in the Milky Way galaxy approximately seven and a half light-millennia from Earth. The oldest staris located in the southern part (15:23-0901) of Constellation Libra, the Scales of Justice — south of Mu Serpentis and north of Gamma Librae. Because of its great distance from Earth, HE 1523-0901 is cannot be seen with the unaided eye, despite being a highly evolved and luminous bright giant.
It is thought to be a second generation Population II, or metal-poor, star ([Fe/H] = −2.95). The oldest star was found in the sample of bright metal-poor halo stars from the Hamburg/ESO Survey by Anna Frebel and collaborators.
The star’s age, as measured by ESO’s Very Large Telescope, is 13.2 billion years. This makes it the oldest object yet discovered in the galaxy and nearly as old as the estimated age of the universe itself (13.7 billion years as measured by WMAP). This oldest staris the first star whose age was determined using the decay of the radioactive elements uranium and thorium in tandem with measurements of several neutron capture elements.
A halo field star, HE 1523-0901 appears to be even older than the ancient stars found in globular clusters. Extremely scarce in elements heavier than hydrogen and helium (“metals”), HE 1523-0901 was found as part of a search for metal-poor halo stars in the Hamburg/ESO Survey, which gave it its “HE” designation in combination with this oldest star position.