An article accepted for publication in “The Astrophysical Journal” describes the discovery of a galaxy called CR7 seen as it was at the time of the early universe in which first-generation stars were found. This research was carried out mainly using ESO’s Very Large Telescope but data collected by the W. M. Keck Observatory, the Subaru Telescope and the Hubble Space Telescope were also used.
So far, the existence of first generation of stars was only a theoretical concept. They are known as Population III stars because astronomers had already classified the Milky Way stars as Population I and Population II, depending on their characteristics, even if they are younger.
A team led by David Sobral, from the Institute of Astrophysics and Space Sciences, the Faculty of Sciences of the University of Lisbon in Portugal, and Leiden Observatory in the Netherlands, used the VLT to observe ancient galaxies. We’re talking about a period known as reionisation, because the light of the first stars interacted with the gas present in great abundance in the universe ionizing it and therefore separating electrons from protons.
By using the VLT and the other telescopes, the astronomers discovered several very bright and very young galaxies. Among them the brightest one is called CR7. This galaxy is so bright because of stars that were very huge and were created by the primordial hydrogen formed after the Big Bang. They’re the first stars that created other heavier elements.
The VLT’s X-shooter and SINFONI (Spectrograph for INtegral Field Observations in the Near Infrared) instruments found strong emission of ionized helium in the galaxy CR7 but no sign of heavier elements. This is evidence that there’s a group of Population III stars because they contain only hydrogen, helium and some traces of lithium, the elements created after the Big Bang.
David Sobral and his team have planned further observations with the VLT, Hubble and also ALMA to verify their discovery. Finding the first stars is difficult because they could reach masses hundreds of times that of the Sun, which means that their life was very short because they consumed hydrogen incredibly fast.
Observing star first generation is important because they show the first phase of creation of heavy elements. To be clear, those are all the elements other than hydrogen, helium and lithium, the same ones that were scattered around the universe by supernovae that marked the end of those stars. They’re the same elements we are made of too.
