Of the many mysteries in astronomy, one of the most exciting is the long-sought observation of Population III stars. These were the first stars that shone in the universe, but we are yet to have observational evidence for their existence.
Although not an observation, astronomers may have now found some compelling indirect evidence of these stars. They detected a cloud of gas with only a small amount of heavy elements like carbon and oxygen, and it was observed as it was only 1.8 billion years after the Big Bang.
“Heavy elements weren’t manufactured during the Big Bang, they were made later by stars,” lead researcher Neil Crighton, from Australia’s Swinburne University of Technology’s Center for Astrophysics and Supercomputing, said in a statement. “The first stars were made from completely pristine gas, and we think they formed quite differently from stars today.”
Hydrogen and Helium (with a small amount of lithium) formed in the primordial nucleosynthesis, but every other element (called metals in astronomy) was formed through nuclear fusion. From the calcium in our bones to the oxygen we breathe, most of the elements we see in the natural world were formed in the heart of ancient stars. Every generation of stars enriches the universe with heavy elements.
Population III stars were not only metal-free but they were also huge: Each star was between 10 to 100 solar masses, with other studies suggesting stars 1,000 and even 10,000 times heavier than our Sun. These stars would produce spectacular supernovae, which would spread metals throughout the cosmos.
“This is the first cloud to show the tiny heavy element fraction expected for a cloud enriched by the first stars,” said Professor John O’Meara, who is presenting the results at the American Astronomical Society meeting in Florida today.
The evidence is valid but far from overwhelming. “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,” added 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.”
The case of the unseen Population III stars is still unsolved, but we are getting closer to a solution every day. Next-generation telescopes should be able to directly observe them, though. In fact, the detection of Population III stars is a goal of NASA's James Webb Space Telescope, which will launch in 2018.