Accurately measuring the age of low-mass, hydrogen burning stars is notoriously difficult, but now astronomers say they have come up with a technique for measuring those difficult stars using white dwarfs, reports the LA Times. A white dwarf is a star that has burned through all of its hydrogen, shed its outer layers, and become a dense lump of carbon and oxygen, and astronomers consider them relatively simple objects to measure. Jason Kalirai from Baltimore's Space Telescope Science Institute compared newly formed white dwarfs from the inner halo of the Milky Way with a well-studied cluster of stars called Messier 4.
Because more massive stars burn faster, Kalirai was able to calculate how old the stars were that became the white dwarfs. From there, he was able to figure out how old the stars in the inner halo were: 11.4 billion years (plus or minus 700 million years). "If we want to assess when components of the Milky Way formed, we need the ages of the stars," said Kalirai. You can check out an abstract of Kalirai's original article in Nature.