A team of astronomers led by Ph.D. student Fred Robert and Professor Michael Murphy from the Swinburne University of Technology in Melbourne, Australia, have discovered what they describe as a cloud of “metal-free gas” deep in the universe.
The pristine gas cloud, which the researchers call LLS 1723 (Layman Limit System 1723), is apparently a fossil relic from the Big Bang that can, potentially, provide unprecedented data on the origins of the first galaxies in the universe.
It is indeed a rare and significant find, in that the gas cloud has somehow remained untouched by heavy elements – the cosmic waste left behind by exploding stars, or supernovae – even though 1.5 billion years have passed since the cosmic exp[losion.
“Everywhere we look, the gas in the universe is polluted by waste heavy elements from exploding stars,” the Swinburne University website quotes Robert as saying.
“But this particular cloud seems pristine, unpolluted by stars even 1.5 billion years after the Big Bang,” Robert told the website.
“If it has any heavy elements at all, it must be less than 1/10,000th of the proportion we see in our Sun,” he said, adding that “this is extremely low – the most compelling explanation is that it’s a true relic of the Big Bang.”
The researchers, who had access to the W. M. Keck Observatory in Hawaii, made full use of the facility’s instruments, including the Echellette Spectrograph and Imager (ESI) and the High-Resolution Echelle Spectrometer (HIRES), to study LLS 1723 in the background of the spectrum originating from a quasar behind it.
A quasar is a massive celestial object that is extremely bright, it’s luminosity emanating from gasses getting sucked into a massive blackhole it contains.
A Blackhole can range in mass from millions to billions of times the Sun’s mass in different quasars, and as gas falls into it huge amounts of energy, which can glow thousands of times brighter than the Milky Way, is released.
“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 the Keck telescope,” added the Ph.D. student.
The discovery may have been fortuitous, but it does motivate more focused searches in the future, “instead of relying on further serendipitous discoveries or large samples of existing high-resolution quasar spectra,” say the authors of the research paper.
While the paper, entitled “Exploring the origins of a new, apparently metal-free gas cloud at z = 4.4,” is pending publication in the science journal Monthly Notices of the Royal Astronomical Society (MNRAS), a preprint can be viewed here.
Prof Murphy believes that the discovery paves the way for more surveys of such Big Bang relics to better understand the birth of the universe.
“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,” said the Swinburne professor.
Prior to the LLS 1723, only two other fossil gas-clouds were known to astronomers; they discovered in 2011 by co-authors of the Swinburne study, Professor Michele Fumagalli, an astrophysicist at Durham University, and Prof John O’Meara, formerly attached to St. Michael’s College.
“Those 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,” Professor O’Meara said. “Now it’s fantastic to finally discover one systematically.”
The project was funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program.
Managed by the California Association for Research in Astronomy, the W.M. Keck Observatory is a non-profit organization with representation from Caltech and the University of California (UC).
“Australian access to the W. M. Keck Observatory has been made available through Astronomy Australia Limited via the Australian Government’s National Collaborative Research Infrastructure Strategy, via the Department of Education and Training, and an Australian Government astronomy research infrastructure grant, via the Department of Industry, Innovation and Science,” acknowledge the authors in the paper.
The array of instruments at the Hawaiian observatory include:
- MOSFIRE – Multi-Object Spectrometer for Infra-Red Exploration
- DEIMOS – Deep Extragalactic Imaging Multi-Object Spectrograph
- HIRES – High-Resolution Echelle Spectrometer
- KCWI – Keck Cosmic Web Imager
- LRIS – Low-Resolution Imaging Spectrograph
- LWS – Long Wavelength Spectrometer for the Keck I telescope
- NIRC – Near Infrared Camera for the Keck I telescope
- NIRC-2 – second-generation Near Infrared Camera
- NIRES – Near-Infrared Echellette Spectrometer
- NIRSPEC – Near-Infrared Spectrometer for the study of very high redshift radio galaxies
- OSIRIS – OH-Suppressing Infrared Imaging Spectrograph (source: Wikipedia)