According to a Swinburne University of Technology-led study, the newly-discovered relic cloud of gas is unpolluted by stars even 1.5 billion years after the Big Bang.
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. Image credit: TNG Collaboration.
“Everywhere we look, the gas in the Universe is polluted by waste heavy elements from exploding stars,” said study lead author Dr. P. Frederic Robert, Ph.D. student at Swinburne University of Technology.
“But this particular cloud seems pristine, unpolluted by stars even 1.5 billion years after the Big Bang.”
“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 co-authors used two instruments — the Echellette Spectrograph and Imager (ESI) and the High-Resolution Echelle Spectrometer (HIRES) – at W. M. Keck Observatory on Maunakea, Hawaii, to observe the spectrum of a quasar called PSS 1723+2243 behind the gas cloud LLS 1723.
PSS 1723+2243, 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 LLS 1723 can be seen.
“We targeted quasars where previous researchers had only seen shadows from hydrogen and not from heavy elements in lower-quality spectra,” Robert said.
“This allowed us to discover such a rare fossil quickly with the precious time on Keck Observatory’s twin telescopes.”
LLS 1723 is one of only three fossil clouds known in the Universe; the two other clouds were discovered in 2011.
“The first two were serendipitous discoveries, and we thought they were the tip of the iceberg,” said study co-author Dr. John O’Meara, chief scientist at Keck Observatory.
“But no one has discovered anything similar — they are clearly very rare and difficult to see. It’s fantastic to finally discover one systematically.”
“It’s now possible to survey for these fossil relics of the Big Bang,” said study co-author Professor Michael Murphy, an astronomer at Swinburne University of Technology.
“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.”
The study will be published in the Monthly Notices of the Royal Astronomical Society.
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P. Frederic Robert et al. 2018. Exploring the origins of a new, apparently metal-free gas cloud at z = 4.4. MNRAS, in press; arXiv: 1812.05098
