An international team of researchers discovered a star that is among the least polluted by heavy elements. Such stars are extremely rare survivors of the early ages of the universe. At that time, the gas those stars formed from hadn’t yet been contaminated by the remnants of successive generations of dead stars. This new discovery opens a window onto star formation at the beginning of our universe.
For the study of the early universe, astronomers have different methods at their disposal. One is to look far into the universe and back in time, to see the first stars and galaxies growing. Another option is to examine the oldest surviving stars of our home galaxy, the Milky Way, for information from the early universe. The “Pristine” survey, led by Nicolas Martin from the University of Strasbourg, France and Else Starkenburg at Leibniz Institute for Astrophysics, Germany is looking for exactly these pristine stars. The team uses CFHT for their observations.
The early universe contained almost exclusively hydrogen and helium. Throughout the life of any star, fusion takes place in the core and creates elements heavier than helium, such as carbon, oxygen, calcium or iron. When these stars explode at the end of their lifetime, they enrich the surrounding gas with these “heavy” elements.
This newly enriched gas serves as the birthplace for the next generation of stars.
Each generation becomes more and more enriched with heavy elements created by their ancestors. Our sun, for example, is made up of about 2 percent of these heavy elements. However, very old stars contain very small quantities of heavy elements. They are extremely rare and extremely difficult to find in our cosmic neighborhood.
The discovery of the star unveiled by the Pristine team was made possible thanks to a new mapping of the night sky conducted at Canada-France-Hawaii Telescope. The Pristine team uses Megacam at CFHT to observe a small part of the ultra-violet light that is very sensitive to the percentage of heavy elements and enables the distinction of rare, pristine stars from the much more common stars polluted with heavy elements.
The team estimates that less than one star in a million is as pristine as the newly discovered star. Follow up observations with spectrographs of the Isaac Newton Group, located in Spain, and the European Southern Observatory, located in Chile, confirmed that star Pristine_221.8781+9.7844 is almost void of heavy elements, with the concentration of heavy elements being 10,000 to 100,000 times lower than those found in the atmosphere of our sun.
This star, whose discovery is presented in a publication of the Monthly Notices of the Royal Astronomical Society, brings strongly needed constraints on star formation models of the very first stars and opens a window onto an epoch that is still poorly understood. The discovery of Pristine_221.8781+9.7844 at the start of the Pristine project bodes well for the discovery of many such stars in the years to come.
