Revealed the origin of a jewel of stellar archeology


An international team with scientists from Institute of Astrophysics of the Canary Islands (IAC) has confirmed the primordial origin of an ancient star in the Milky Way with the ESPRESSO instrument.

The stars with a lower metallic content are considered the oldest in the Milky Way, formed just a few hundred million years after the Big Bang. A time that is considered fleeting compared to the age of the Universe. These stars are authentic living fossils that they carry encoded in their chemical composition the first stages of evolution of the Universe.

The star SMSS1605-1443 was discovered in 2018, and identified as one of the oldest in the galaxy due to its chemical composition, but its true nature was unknown. Now, thanks to the combined effort of several European research groups and the use of the ESPRESSO spectrograph, installed on the VLT telescope, has deduced the origin of this jewel of stellar archeology. The results of this research are published in the journal Astronomy & Astrophysics (A&A).

“It was a surprise to discover, thanks to ESPRESSO and the VLT (Very Large Telescope), that this object was actually a double (or binary) star. Something that, until recently, it was believed that it did not occur in most of these very old stars“, says David Aguado, lead author of this work and researcher at the University of Florence.

The research team has used the ESPRESSO instrument which, given its high precision, has made it possible to follow the small variations in the speed of this star, which confirm its binary nature, but leave that of its companion open. These types of stars are believed to have formed from the material processed inside the first massive stars, ejected in supernova explosions in the early stages of the formation of the Milky Way. As a consequence, these stars have a low iron content but a high carbon content, generated inside the first massive stars.

The high resolution of the ESPRESSO instrument has made it possible to analyze in detail the relative composition of carbon isotopes, which yields new information regarding the origin of this object.

The IAC researcher Jonay González Hernández, co-author of this work, clarifies it’s a statement: “The key was given to us by the ratio of carbon-12 and carbon-13 that we found in the atmosphere of this star. The relative amount of these two isotopes proves that the internal processes of the star have not altered its original composition. It’s like have an intact sample of what the environment in which this star formed was like more than ten billion years ago.”

“This discovery must be understood in the context of a project that began a decade agoin which we have studied in detail all the known stars of this rare class until we come across this marvelous finding, which helps us to better understand the chemical evolution of the Universe”, reports Carlos Allende Prieto, IAC researcher and co-author of this worked.