KISSIMMEE, FLORIDA—Astronomers have spotted evidence of how the very first generation of stars seeded the universe with elements forged from the pristine hydrogen and helium produced by the big bang. Last year observers found a distant galaxy that seemed to have patches of stars made up of hydrogen and helium but nothing else. Making significant amounts of heavier elements, such as carbon, oxygen, and iron, is thought to have taken multiple generations of stars, so these appeared to be some of the very earliest stars. Today, a team of astronomers told the American Astronomical Society meeting here that they’ve found a cloud of gas that has tiny amounts of heavy elements, just as you would expect if primordial stars—so-called population III stars—had burned out, exploded, and spread their ingredients through the previously pristine gas cloud. To probe the cloud, the team used an even more distant quasar—a hugely bright light source powered by a supermassive black hole—as a backlight. As the quasar’s light passed through a galaxy that existed 1.8 billion years after the big bang, atoms in its gas clouds absorbed some wavelengths, leaving a fingerprint of the elements present. Analyzing the light with the European Southern Observatory’s Very Large Telescope in Chile, the researchers found the amount of elements heavier than helium to be less than one-thousandth that in the sun’s neighborhood, and the ratio of carbon to silicon is just what would be expected of exploded population III stars.