Astronomers from the University of Notre Dame have been studying a group of very old stars and believe they have learned something about the composition of the first stars in the universe, which we have not been able to observe yet.
In a paper, published in the Astrophysical Journal, the researchers discussed the observations of carbon-enhanced, metal-poor stars rich in nitrogen and oxygen (CEMP-no). These objects are some of the most chemically primitive stars ever observed, indicating that they must have formed before the universe became enriched in heavier elements.
“The CEMP-no stars we see today, at least many of them, were born shortly after the Big Bang, 13.5 billion years ago, out of almost completely unpolluted material,” lead author Jinmi Yoon said in a statement. “These stars, located in the halo system of our galaxy, are true second-generation stars – born out of the nucleosynthesis products of the very first stars.”
Most of the atomic nuclei that formed in the Big Bang were hydrogen and helium. Heavier elements, like carbon and iron for example, are instead formed in stars and then spread out around galaxies when said stars go supernova.
The CEMP-no stars are believed to have been enriched by the heavier elements produced by the first stars. The astronomers studied about 300 stars outside the disk of the Milky Way, and by looking at their light in high-resolution, they were able to work out exactly what these CEMP-no stars are made of.
“We’re analyzing the chemical products of the very first stars by looking at what was locked up by the second-generation stars,” said Professor Timothy Beers, the Notre Dame chair in Astrophysics. “We can use this information to tell the story of how the first elements were formed and determine the distribution of the masses of those first stars. If we know how their masses were distributed, we can model the process of how the first stars formed and evolved from the very beginning.”
The first stars were much bigger on average than stars in the recent universe. They shined brightly and died young. Our instruments are yet to observe these primordial stars, but the James Webb Space Telescope, which will be launched in 2018, has a good chance to finally see them.