US scientists have found two interstellar clouds of original gas, which contain only original elements created moments after the universe's birth.
Unlike everything else in the universe — the gas clouds have never mingled with elements forged later in stars.
The existence of pristine gas that formed minutes after the Big Bang explosion some 13.7 billion years ago, had been predicted, but never before observed.
The clouds, which are located about 12 billion light-years from Earth within the constellations Ursa Major and Leo, were found serendipitously during an ongoing study to characterise gas in distant galaxies.
In analysing the light coming from quasars (active nuclei of distant galaxies), astronomers realised the rays had passed through gas that contained only hydrogen and deuterium, elements that formed minutes after the Big Bang.
The surprise was that the clouds contained nothing else — no carbon, no nitrogen, no silicon, no iron — none of the heavier elements forged in stars and spread throughout the universe.
"In some respect we were searching for this, but we had been doing so for years and had been unsuccessful so the discovery was a very welcome surprise," says astronomer and study co-author Jason Prochaska, from the University of California's Lick Observatory.