There’s a Star That Dates Back to the Early Universe

HE 1523-0901 is one of the oldest stars known. Uranium and thorium in its atmosphere act like a radioactive clock, and they point to an age of about 13.2 billion years, with a sizable margin of error. It formed when the universe was still figuring itself out, from gas enriched by only a few earlier generations of stars. To put that in perspective, hydrogen and helium nuclei formed within minutes after the Big Bang, but heavier elements took hundreds of millions of years to appear. In a way, it’s a fossil of the early universe, still glowing today.