“This research demonstrates how the chemical information preserved in stellar atmospheres can be used as a fingerprint to reconstruct the evolutionary history of a galaxy,” explains Sara Vitali, PhD candidate in Astrophysics at UDP.
An international team of astronomers, led by the Institute of Astrophysical Studies at Diego Portales University, successfully reconstructed the chemical evolution of the Sagittarius dwarf spheroidal galaxy with unprecedented detail. This ancient companion of the Milky Way is currently in the process of dissolving due to its interaction with our galaxy.
The study titled “The Pristine Inner Galaxy Survey (PIGS) XI: Revealing the chemical evolution of the interacting Sagittarius dwarf galaxy”, soon to be published in the specialized scientific journal Astronomy & Astrophysics (A&A), constitutes the core of Sara Vitali’s doctoral thesis. Vitali is a PhD student in Astrophysics at Diego Portales University, set to complete her studies in June of this year. The research is based entirely on observations conducted in Chile, using the FLAMES spectrograph of the European Southern Observatory (ESO), installed on the Very Large Telescope (VLT) in the north of the country.
“This work presents the most extensive and homogeneous high-resolution optical analysis conducted to date on stars in the central core of the Sagittarius galaxy,” explains Sara Vitali, who holds a degree in Physics from the University of Turin (Italy) and a Master’s in Astrophysics from the University of Potsdam (Germany). In total, 111 giant stars were studied, carefully selected from a catalog of over 50,000 possible members, thanks to data from the international Pristine Inner Galaxy Survey (PIGS), of which Vitali is a member.
The observations made it possible to measure the abundance of up to 14 different chemical elements per star (including sodium, magnesium, calcium, barium, and europium) and to estimate their ages. This allowed the researchers to trace a chronological evolution of the galaxy’s star formation process.
The results show that Sagittarius had a richer and more prolonged evolutionary history than previously thought. During its first billion years, it formed stars rapidly and efficiently, resulting in an old, metal-poor stellar population. But the most revealing finding is that this activity did not stop—the galaxy continued forming stars in later episodes, even as recently as 4 billion years ago.
This demonstrates that, despite having lost much of its gas due to interactions with the Milky Way, Sagittarius managed to maintain favorable conditions for continuing to generate new generations of stars. “This research demonstrates how the chemical information preserved in stellar atmospheres can be used as a fingerprint to reconstruct the evolutionary history of a galaxy,” adds Vitali.
From UDP, renowned astronomer Paula Jofré—Director of the PhD Program in Astrophysics and Sara Vitali’s thesis advisor—highlights the structural importance of the work: “This is the final article of Sara’s PhD, and her research clearly shows how we are building strong talent in stellar spectroscopy from Chile—a discipline with a long-standing tradition worldwide, which is gradually reaching a critical mass in our country to develop a wide range of star-related projects, from stars as hosts of planets to stars as tracers of galactic histories.”
Additionally, the study has direct implications for broader research on the history of galaxies. “Sara’s work has been important in laying the groundwork for what we’re developing in galactic phylogenetics. It is one of the studies that contributed tools, data, and specific cases to the Millennium Nucleus ERIS, which I lead. Now, with this chemical dataset from Sagittarius, we plan to see how the phylogenetic trees compare with those we have built for the Milky Way and thus contrast the histories of both galaxies,” adds Jofré.
This study is the result of a collaboration between Álvaro Rojas, Principal Investigator, and Paula Jofré, Director—both from the Millennium Nucleus ERIS—initiated by the ERIS team and strengthened through spectral analysis contributions by Claudia Aguilera, a researcher from the same center. Beyond its scientific impact, the work highlights the potential of the astronomical infrastructure established in Chile. “All observations were conducted entirely using telescopes located within national territory, taking advantage of the privileged skies in the north. And although it was an international collaboration, a large part of the work was carried out from UDP, which demonstrates our country’s growing capacity to lead world-class research in astrophysics,” concludes Vitali.