Dr. Timothy C. Beers, Notre Dame Chair in Astrophysics, and an international team of astronomers have discovered a low-mass star in the Milky Way galaxy that could help explain the origin of elements in the universe. The star exhibits the peculiar chemical abundance ratios associated with the process of creating new atomic nuclei (nucleosynthesis) in a first-generation very-massive star, according to a University press release.
The group of astronomers published their study, entitled “A chemical signature of first-generation very-massive stars,” in the Aug. 22 issue of the journal "Science."
The star has a unique set of chemical ratios that have never been seen before, Beers said. Using high-resolution spectroscopic instruments on the Subaru Telescope located in Hawaii, Beers and his team, comprised of astronomers from Japan and Korea, observed a star in the halo region of the Milky Way galaxy 300 parsecs (or about 1000 light years) away.
“We are essentially reconstructing a stellar history from the chemistry of objects we discovered today,” Beers said.
The study of ancient stars and their origins is known as Galactic archaeology, he said.
“This was the first example of an ancient star whose elements had to have been produced by another star that was much more massive, maybe several hundred times the mass of the sun,” Beers said.
Beers compared the formation of early stars to the pollution of a river.
“You have a massive star that was formed out of pure Big-Bang material, pristine, hydrogen, helium, a little bit of lithium [and] nothing else," he said. "When that star exploded, it created heavier elements, which then polluted pristine gas around it. It’s that polluted gas which carries the fingerprint of the progenitor that the star we discovered formed from.
“If you can go back and find the almost-pristine, perfect, unpolluted stars, you know you have to be at the beginning,” Beers said.
The star is approximately 12- to 13-billion-years-old, approaching the age of the 14-billion-year-old universe, Beers said.
“The chemistry tells us this star was born at least 10-billion-years-ago, because if it were born any later, it would have formed out of gas that was polluted to a higher degree,” Beers said. “When people think ancient, they often think far away. What many people find fascinating is that these are objects in our own galaxy. They’re ... right here. It’s just that we can recognize them as markers of this early history. You don’t have to go to the edge of the universe to study the very beginning of it, in the chemical sense they are pristine fossils."
According to a University press release, the star is the first such star identified in the Milky Way. The astronomers hope to discover more stars similar to this one, and refine their analysis in order to confirm the existence of very-massive stars in the first generation. Such stars could have contributed to the development of super-massive black holes like the one at the center of the Milky Way.
Beers said he is currently searching the universe for more stars like this one using the Large Binocular Telescope in Arizona, which is operated by a research consortium.
“This discovery is one of many along the way,” Beers said.
