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Astronomers find pristine gas from the big bang
Posted: 10 November 2011

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Two clumps of gas that formed in the opening moments of the Universe's existence have been found by astronomers using telescopes at the W. M. Keck Observatory, the first time that gases never involved in star formation have been detected.

Only the very lightest elements such as hydrogen and helium were formed in the big bang; heavier elements were synthesized a few hundred million years later in the hot furnaces of the first stars and subsequent stellar generations. Although the newly discovered gas clouds were found two billion years after the big bang, they represent the simplest material that existed just seconds after the Universe was born.

“It’s quite exciting, because it’s the first evidence that fully matches the composition of the primordial gas predicted by the big bang theory,” says Michele Fumagalli of the University of California, Santa Cruz, lead author of a paper on the findings published online in Science today.

The two pristine gas clouds found by astronomers could sit in one of the filamentary regions visible around galaxies, represented here in a frame from a computer simulation. Image: Ceverino, Dekel & Primack

The team used the HIRES spectrometer on the 10-metre Keck I telescope to analyse light from a distant quasar that was absorbed by the intervening gas clouds. By looking at the way in which the light was absorbed, the astronomers could determine the composition of the constituent elements in the gas cloud, finding nothing other than hydrogen and its heavier isotope, deuterium.

"It was an exciting surprise to see gas with such a lack of heavy elements two billion years after the big bang," Fumagalli tells Astronomy Now. "Prior to this discovery, the lowest measurements of metal abundance in the Universe were about one-thousandth the metallicity of the Sun [metallicity describes how enriched stellar objects are in elements heavier than hydrogen and helium]. Based on this empirical evidence, people started to believe in a 'floor' to the metallicity of cosmic structures, essentially that nothing could be less than one-thousandth the solar metallicity."

Yet the newly discovered gas cloud has just one ten-thousandth of the Sun's metallicity. The finding may point astronomers to the sites of so-called cold flows, streams of as yet never detected cold gas that played a crucial role in building galaxies.

"We know that galaxies need a continuous replenishment of fresh fuel for the formation of stars," explains Fumagalli. "Modern theories and simulations say that this accretion occurs along filaments of cold gas that is not highly enriched with heavy elements, but no direct observations exist to confirm these models. The two gas clouds we have found are composed by cold and pristine gas, similarly to what predicted for these cold flows. This is tantalizing, but at the moment, we do not know if the gas clouds lie in empty regions or in proximity of galaxies. We need to take images and other spectra of that part of the sky to answer this question."