Free Astronomy Magazine March-April 2023

24 MARCH-APRIL 2023 ASTRO PUBLISHING (IAC) and former researcher at the University of Florence-NEFERTITI group, first author of this work pub- lished in the January 2023 issue of the journal Astronomy & Astro- physics , explains: “It was a real sur- prise to discover that this star was actually a long period binary star, which was not foreseen and which requires a revision of the theory of formation of the first stars.” Funda- mental was the use of the ESPRESSO spectrograph which, thanks to its high precision, has made possible to follow the small variations in the speed of this star due to its orbital motion around its companion, which remains nevertheless unknown. These stars have a low iron content but a high carbon content, and are called CEMP-no in the astronomical jargon. They are thought to have formed from material processed from the interior of the first massive stars and ejected in the explosion of supernovae in the early stages of the formation of the Milky Way. “All the oldest stars we know belong to the CEMP-no class and I like to remem- ber that with Piercarlo Bonifacio we discovered the prototype of this class of stars back in 1997,” under- lines Paolo Molaro, astronomer of INAF-Trieste, co-author of this work and principal investigator of the re- search programme. The high resolution of the instru- ment allowed a detailed analysis of the relative composition of the car- bon isotopes which provided new information on the origin of the el- ements observed in the atmosphere of the star. Elisabetta Caffau, an Italian as- tronomer who works at Paris Ob- servatory, explains: “The key was provided to us by the relationship between Carbon-12 and Carbon-13. The relative quantity of these two isotopes demonstrates that the in- A near-pristine star found to be binary by IAC − Science Communication and Culture Unit S tars with very low content of chemical elements are consid- ered to be the older stars in the Milky Way. Formed a few hundred million years after the Big Bang, a very small time compared to the age of the Universe, these stars are real fossils which encode the first phases of the chemical evolution of the Uni- verse in their atmosphere. The star SMSS1605-1443, discovered in 2018, was identified as one of the earliest stars in the galaxy, but its true nature was unknown. Now, thanks to the joint effort of several European research groups and the use of the ESPRESSO spectrograph, capable of operating with any of the four VLT telescopes in Chile, it has been possible to understand the al- most primordial origin of this ar- chaeological stellar jewel. David Aguado, currently Ramón y Cajal Ad- vanced postdoctoral fellow at the In- stituto de Astrofísica de Canarias