CEA News, December 2018

Simulation of galaxies and gas in the Universe. Credit: TNG Collaboration.

Big Bang “fossil” discovered

A relic cloud of gas, orphaned after the Big Bang, has been discovered in the distant universe by astronomers using the world’s most powerful optical telescope. Durham University’s Centre for Extra-galactic Astronomy is a partner in the research that offers new information about how the first galaxies in the Universe formed. The discovery of the rare galactic fossil was led by PhD student Fred Robert and Professor Michael Murphy at Swinburne University of Technology, in Australia.

Big Bang relic

“Everywhere we look, the gas in the Universe is polluted by waste heavy elements from exploding stars,” said Mr Robert. “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.”

The researchers used the twin 10-metre telescopes of the WM Keck Observatory in Hawaii to observe the spectrum of a quasar behind the gas cloud.

Supermassive black hole

The quasar – the 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.

Simulation of galaxies and gas in the Universe. Credit: TNG Collaboration.
“We targeted quasars where previous researchers had only seen shadows from hydrogen and not from heavy elements in lower-quality spectra,” Mr Robert said. “This allowed us to discover such a rare fossil quickly with the precious time on the Keck telescope.”

Co-authors of the new research, Professor Michele Fumagalli in Durham University’s Institute for Computational Cosmology and Centre for Extragalactic Astronomy, and Professor John O’Meara, formerly at Saint Michael’s College, USA, and now Chief Scientist at the WM Keck Observatory, discovered the only two other fossil clouds known in 2011.

First stars and galaxies

Professor Fumagalli said: “At present, our latest discovery is one of only three gas clouds know to have survived unpolluted by stars. Their existence, and hence their discovery, provides insight into how elements formed and spread out in the Universe, thereby providing insight into the origin of the first stars and galaxies.”
Professor O’Meara added: “Those (2011 discoveries) 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. Now it’s fantastic to finally discover one systematically.”

Early Universe

“It’s now possible to survey for these fossil relics of the Big Bang,” said Professor Murphy 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 research was funded by an Australian Research Council Discovery Project grant and Professor Fumagalli's contribution was partially funded by a European Research Council grant. The paper, “Exploring the origins of a new, apparently metal- free gas cloud at z = 4.4”, is to be published by Monthly Notices of the Royal Astronomical Society. A preprint version is available here.