Researchers from Australia and the USA have discovered a distant, ancient cloud of gas that may contain the signature of the very first stars that formed in the Universe, in research to be published in Monthly Notices of the Royal Astronomical Society. The research was undertaken by Dr Neil Crighton and Professor Michael Murphy from Swinburne University of Technology in Melbourne, Australia, and Associate Professor John O’Meara from Saint Michael’s College in Colchester, Vermont, USA. Professor O’Meara presented the results at the American Astronomical Society meeting.
The gas cloud has an extremely small percentage of heavy elements, such as carbon, oxygen and iron — less than one thousandth the fraction observed in the Sun. It is many billions of light years away from Earth, and is observed as it was just 1.8 billion years after the Big Bang. The observations were made by the Very Large Telescope in Chile.
“Heavy elements weren’t manufactured during the Big Bang, they were made later by stars,” says lead researcher, Dr Neil Crighton, from Swinburne University of Technology’s Centre for Astrophysics and Supercomputing. “The first stars were made from completely pristine gas, and astronomers think they formed quite differently from stars today.”
The researchers say that soon after forming, these first stars — also known as Population III stars — exploded in powerful supernovae, spreading their heavy elements into surrounding pristine clouds of gas. Those clouds then carry a chemical record of the first stars and their deaths, and this record can be read like a fingerprint.
“Previous gas clouds found by astronomers show a higher enrichment level of heavy elements, so they were probably polluted by more recent generations of stars, obscuring any signature from the first stars,” Dr Crighton says. “This is the first cloud to show the tiny heavy element fraction expected for a cloud enriched only by the first stars,” said one of the co-authors, Swinburne’s Professor Michael Murphy.
Reference: Neil H. M. Crighton, John M. O’Meara, Michael T. Murphy. Possible Population III Remnants at Redshift 3.5. Monthly Notices of the Royal Astronomical Society, 2015