ScienceNow

30 April 2003

Chemistry at 11 Billion Light-Years

The modern ingredients of the universe were well established just 2.5 billion years after the big bang, a new study suggests. The world's largest telescopes have unveiled a rich broth of heavy elements in the gas of a distant galaxy, in the same proportions seen in our sun. Most of the elements arose when very massive stars exploded, astronomers believe.

Stars are chemical chefs, cooking elements as heavy as iron during fusion at their cores. Giant stars consume their nuclear fuel quickly and then explode as supernovas. The fierce heat forges other elements as particles combine in a frenzy of reactions. By this process of nucleosynthesis, generations of stars have transformed a fraction of the big bang's hydrogen and helium into the elements of our world. However, astronomers weren't sure how quickly this happened in the early cosmos, because no one had spotted an array of heavy elements in remote galaxies.

Now, astronomer Jason X. Prochaska of the University of California, Santa Cruz, and colleagues have made the first such measurement. The team used the 10-meter Keck Telescopes on Mauna Kea, Hawaii, to study distant quasars, bright beacons of energy unleashed by matter falling into huge black holes. As quasar light passes through other galaxies on its way to Earth, chemical elements in the galaxies' gas absorb some colors, imprinting unique signatures on the light's spectrum.

Among 50 quasars, one showed an especially rich pattern of heavy elements. As the team reports in the 1 May issue of Nature, the quasar illuminated more than 25 distinct chemical fingerprints in a galaxy about 11.1 billion light-years away, dating to an era 2.5 billion years after the big bang. The light reveals rarely seen elements such as boron, germanium, tin, and lead. "We're covering just about every major process of nucleosynthesis in this one galaxy," Prochaska says. The ratios of certain elements suggest that stars at least 15 times more massive than our sun exploded to seed the galaxy with silicon, sulfur, zinc, and other metals. Moreover, the ratios of elements are similar to those in our sun, suggesting that the Milky Way and the distant galaxy were chemically enriched in the same way.

"This is quite a jump forward in our understanding of nucleosynthesis and star formation in the early universe," says astronomer John Cowan of the University of Oklahoma, Norman. He's encouraged by Prochaska's estimate that astronomers should be able to conduct similar analyses for at least 2% of all distant galaxies.

--ROBERT IRION