Space Clocks - January through April 2001
These white dwarf stars, located 5,600 light-years away in the constellation Scorpius, are the dimmest and oldest stars in our Milky Way, still cooling after a 12-billion to 13-billion-year existence. White dwarfs cool off at a predictable rate, so scientists can tell a star’s age from its brightness. If, as astronomers theorize, the first stars formed less than 1 billion years after the universe’s birth, these stars clock the universe at 13 billion to 14 billion years old. Astronomers had already calculated this age in 1997, based on the rate at which the universe is expanding. The Hubble photographs verified that their math was correct.