A gas cloud has survived the universe's first 1.5 billion years without being contaminated with elements from stars, making it a pure remnant of the Big Bang. The discovery could help us understand the early universe's development.
In 2011 astronomers observed two gas clouds apparently composed of the original material formed in the Big Bang. The discovery surprised astronomers who expected the debris of stars to have invaded such spaces by the times at which we were seeing them. Even more unexpected was how unusual the pair appeared.
According to Professor Michael Murphy of Australia's Swinburne University of Technology, the first findings were made by chance. Newly identified populations of astronomical objects found in this way usually quickly lead to the identification of others of the same kind, but for seven years searches turned up nothing. Now Murphy has filled this gap, identifying a third such cloud, using a method he anticipates will prove an efficient way to find more examples.
Murphy's discovery, to be reported in the Monthly Notices of the Royal Astronomical Society (preprint available on arXiv), has a redshift indicating we are seeing it as it was 1.5 billion years after the Big Bang. Its gas is too diffuse to have formed any stars of its own which could manufacture heavy elements, and presumably is too far from nearby galaxies for them to sully it.
Without stars, the cloud produces no light. We can observe it only because an even more distant powerful quasar lies beyond it. The absorption spectrum of the quasar's light reveals the cloud's composition.
The quasar was one of 10 Murphy and co-authors investigated because previous studies had indicated they might be illuminating clouds low on heavy elements. The team are confident repeating the work with larger samples will produce more such objects. “That will tell us exactly how rare they are and help us understand how some gas formed stars and galaxies in the early universe, and why some didn’t,” Murphy said in a statement.
At such a great distance it is impossible to prove the cloud has absolutely no heavy elements, but the paper shows they are at least 10,000 times scarcer than in the Sun. Murphy told IFLScience that while it is possible tiny amounts of supernova residue have polluted the cloud, models suggest it is more likely it is entirely pure.
“We're interested not just in the pristine clouds, but the ones that retain the chemical signals from the long-dead first stars,” Murphy told IFLScience. “Having shown we can find gas clouds that hang around for at least 1.5 billion years without interacting, it should be possible to find those that can tell us about the first generation of stars.”