The discovery of a 13 billion-year-old cosmic cloud of gas enabled a team of Carnegie astronomers to perform the earliest-ever measurement of how the universe was enriched with a diversity of chemical elements.

The Big Bang started the universe as a hot, murky soup of extremely energetic particles that was rapidly expanding. As this material spread out, it cooled, and the particles coalesced into neutral hydrogen gas.

The universe stayed dark, without any luminous sources, until gravity condensed matter into the first stars and galaxies.

All stars, including this first generation, act as chemical factories, synthesizing almost all of the elements that make up the world around us. When the original stars exploded as supernovae, they spewed out the elements that they created, seeding the surrounding gas.

Subsequent generations of stars incorporated these elements and steadily increased the chemical abundances of their surroundings.

But the first stars formed in a still pristine, cold universe. Consequently these initial stars produced elements in different proportions than those synthesized by younger stars, which were formed in an environment that was already enriched by earlier generations.

Looking back in time far enough, one may expect cosmic gas clouds to show the tell-tale signature of the peculiar element ratios made by the first stars.

Quasars are tremendously luminous objects comprised of enormous black holes accreting matter at the centers of massive galaxies. Because the gas cloud exists between the quasar and us on Earth, the quasar’s incredibly bright light must pass through it to get to us and astronomers can take advantage of this to understand the cloud’s chemistry.

The team found that the cloud’s chemical makeup was quite modern, and not as primitive as expected if dominated by the first stars.

Although it formed only 850 million years after the Big Bang, its chemical abundances were already as high as those typically seen in cosmic gas clouds that were formed several billion years later.

Apparently, the first generation of stars had already expired by the time the cloud formed Researcher said.

This shows that the universe was rapidly swamped by the chemical products of later generations of stars, even before most of the present day galaxies were in place.


The research was published in Carnegie Institution for Science