Last updated April 1, 2019 at 11:54 am
The rare relic, seemingly untouched since the Big Bang, is only the third pristine gas cloud ever discovered.
Simulation of galaxies and gas in the universe. Within the gas in the (blue) filaments connecting the (orange) galaxies lurk rare pockets of pristine gas – vestiges of the Big Bang that have somehow been orphaned from the explosive, polluting deaths of stars, seen here as circular shock waves around some orange points. Credit: TNG Collaboration
The universe today is a very different place to what it was straight after the Big Bang, however Australian astronomers have found a ‘fossil’ that may give an insight into those early moments in time.
The researchers, from Melbourne’s Swinburne University, have announced the discovery of a relic cloud of gas in the distant universe, described as being pristine and seemingly untouched since the Big Bang.
“Everywhere we look, the gas in the universe is polluted by waste heavy elements from exploding stars,” says Frédéric Robert, who led the finding as part of his PhD research.
“But this particular cloud seems pristine, unpolluted by stars even 1.5 billion years after the Big Bang.”
The newly discovered cloud is only the third of such Big Bang ‘fossils’ ever found.
Over the lifetime of the universe – some 13.7 billion years – supernovae have spewed heavy elements across the galaxies. When astronomers look into space today they usually find gas clouds containing these heavy elements, polluted by the remnants of dead stars.
However, using the massive W. M. Keck Observatory in Hawaii, the researchers have identified a gas cloud almost completely devoid of these heavy elements. And that, they suggest, could mean it is a relic of the very early universe that has since remained untouched.
The results have been published on the pre-print site arXiv, and will be published in the journal Monthly Notices of the Royal Astronomical Society.
“If it has any heavy elements at all, it must be less than 1/10,000th of the proportion we see in our Sun. This is extremely low; the most compelling explanation is that it’s a true relic of the Big Bang.”
Robert and his team used two of Keck Observatory’s instruments – the Echellette Spectrograph and Imager (ESI) and the High-Resolution Echelle Spectrometer (HIRES) – to observe the spectrum of a quasar behind the gas cloud. The quasar, which emits a bright glow of material falling into a supermassive black hole, provides a light source against which the spectral shadows of the hydrogen in the gas cloud can be seen.
“We targeted quasars where previous researchers had only seen shadows from hydrogen and not from heavy elements in lower-quality spectra,” says Robert. “This allowed us to discover such a rare fossil quickly with the precious time on Keck Observatory’s twin telescopes.”
The authors note that while the Big Bang relic explanation is the most compelling, there are two other potential explanations. The cloud could have very trace levels of heavy elements left by hypothesised Population III stars which are thought to contain very little heavy elements, leaving remnants which are below the sensitivity of the Keck Observatory. Another possible explanation is that the gas cloud originally formed in the areas between galaxies out of the intergalactic medium, and is yet to become polluted as it passes through a galaxy for the very first time.
Only two fossil clouds have been discovered previously, in 2011 by John O’Meara, formerly of St. Michael’s College in the UK, and Michele Fumagalli from Durham University.
“The first two were serendipitous discoveries, and we thought they were the tip of the iceberg. But no one has discovered anything similar — they are clearly very rare and difficult to see. It’s fantastic to finally discover one systematically,” says O’Meara.
“It’s now possible to survey for these fossil relics of the Big Bang,” says Robert’s supervisor Michael Murphy. “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.”
