Faculty astrophysicist makes splash among peers

By: Mark Tarnacki
O'Meara gas clouds

Computer simulation of the explosion of the first stars in the universe showing how they send heavy elements out into the young universe. Experimental results in John O’Meara’s recent study with colleagues can be used to test the models. (Credit: Smith, Britton D.; Wise, John H.; O'Shea, Brian W.; Norman, Michael L.; Khochfar, Sadegh)

Saint Michael’s College physics professor John O’Meara has teamed with researchers Neil Crighton and Michael Murphy from Australia in the recent discovery of a distant, ancient cloud of gas that may contain the signature of the very first stars that formed in the universe.

O'Meara, a co-author on the study, will be presenting the results at the American Astronomical Society meeting in Kissimmee, FL, January 4-8, 2016. 

The gas cloud his team discovered 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 distant, and is observed as it was only 1.8 billion years after the Big Bang, say the researchers, whose observations were drawn from data from the Very Large Telescope (VLT), operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile.

“Heavy elements weren't manufactured during the Big Bang, they were made later by stars,” says lead researcher Neil Crighton, from Australia’s Swinburne University of Technology’s Centre for Astrophysics and Supercomputing. “The first stars were made from completely pristine gas, and we think they formed quite differently from stars today.”

The researcher 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. They say the composition of those clouds records information about the first stars and their deaths.

“Previous gas clouds found by astronomers show a relatively high enrichment level of heavy elements, so they were probably polluted by more recent generations of stars, diluting and obscuring any signature from the first stars,” Crighton says.

“This is the first cloud to show the tiny heavy element fraction expected for a cloud enriched by the first stars,” said O’Meara.

The researchers hope to find more of these systems, where they can measure the ratios of several different kinds of elements.

“We can measure the ratio of two elements in this cloud - carbon and silicon. But the value of that ratio doesn't conclusively show that it was enriched by the first stars; later enrichment by older generations of stars is also possible,” said O’Meara.

“By finding new clouds where we can detect more elements, we will be able to test for the unique pattern of abundances we expect for enrichment by the first stars,” he said.

The work will appear in the January 13 edition of the Monthly Notices of the Royal Astronomical Society.

Also at the recent meeting in Florida, O’Meara and another Swinburne researcher, Jeff Cooke, presented other exciting discoveries in their field: Using the world’s largest telescopes, they have discovered ancient cold gas clouds larger than galaxies in the early Universe. The discovery has helped solve a decades-old puzzle on the nature of gas clouds, known as damped Lyman alpha systems, or DLAs. Cooke and O’Meara realized that finding DLA gas clouds in the line of sight to background galaxies would enable measurements of their size by determining how much of the galaxy they cover, according to a Swinburne press release.

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