An article published in the journal “Monthly Notices of the Royal Astronomical Society” describes the discovery of a new family of stars at the center of the Milky Way tha are unusually nitrogen-rich. A team of astronomers from the Liverpool John Moores University (LJMU) made this discovery working on the APOGEE (the Apache Point Observatory Galactic Evolution Experiment) project, which aims to collect infrared data of hundreds of thousands of stars in the Milky Way.
LJMU is a member of the Sloan Digital Sky Survey, an international collaboration that created the most detailed three-dimensional maps of the universe ever produced. In 2014 the fourth survey began with a duration scheduled until 2020. The APOGEE project is part of this collaboration and star observations at infrareds allowed to discover a new population of them, of a type only seen so far in globular clusters.
This new family of stars may have been originally a part of globular clusters that were destroyed during the formation of the Milky Way. Sometimes traces of them remain such as in the case of Terzan 5 but in other cases it’ become impossible to distinguish them, at least until the stars are examined in details such as in the APOGEE project. It’s possible that when the galaxy was young there was an amount of globular clusters even ten times the present.
Infrared observations allow to see through the large amount of dust that blocks the view of the Milky Way’s core in visible light. For this reason, the APOGEE project allows astronomers to collect previously unknown data that can help them better understand how the Milky Way formed and the role of globular clusters in that process. The conclusions could be extended to other galaxies.
A key to this research was the ability to determine the chemical composition of thousands of stars. That allowed the identification of a significant amount of stars different from most of those existing in the Milky Way’s inner regions and in particular for the great abundance of nitrogen. It’s an anomaly that doesn’t have a final explanation but for the moment only a couple of hypotheses.
The astronomers suspect that those stars are the result of the destruction of globular clusters but don’t have enough evidence to be certain. Another possibility is that those stars are the by-product of the first star formation episodes that occurred at the beginning of the Milky Way’s history. The project continues, as well as the observations to gather more data to test these hypotheses.
It’s no coincidence that various studies focused on the exam of the galactic core and certainly there will be more. The results seem to confirm the important role of globular clusters in galaxy formation but the exam of new data might point to different answers. It’s for this reason that surveys such as the Sloan Digital Sky Survey and the APOGEE project are important.
