An article published in recent days in “The Astrophysical Journal” describes a research showing that about 30% of the stars in the Milky Way – which means nearly one in three – moved dramatically from the orbit it had at its birth. This surprising result was achieved by a team of scientists who worked on the Sloan Digital Sky Survey (SDSS) observing for a four-year period 100,000 stars with the SDSS Apache Point Observatory Galactic Evolution Explorer (APOGEE) spectrograph.
Stars also have their own orbits, which for various reasons can be far more complex than that of planets around stars but is roughly around the center of their galaxy. A team of scientists tried to examine the current positions of a group of stars in the Milky Way to see how they moved doing it basing on their chemical composition.
Stars consume their hydrogen producing heavier elements, particularly those much more massive than the Sun, which explode as supernovae scattering elements around space. The consequence is a process of “chemical enrichment” for which each new generation of stars absorbs larger quantities of those elements.
In some regions of the Milky Way there are greater amounts of heavy elements than in other regions. This means that the average amount of heavy elements present in stars varies greatly in different parts of the Milky Way. This different distribution has been exploited by the scientists who carried out this research.
In the end, the analysis of the chemical composition of a star becomes a kind of DNA test that allows tracking its relations with other stars. That’s because the stars born from the same cloud of gas and dust contain very similar amounts of heavy elements, so they can trace their origin.
In this research, its lead author Michael Hayden of the New Mexico State University and his colleagues used the APOGEE spectrograph to map the amount of 15 different elements including carbon, silicon and iron. The result was really surprising because about 30% of the stars examined have a composition which indicates that they were formed in areas of the galaxy far away from their current location.
The researchers offered some preliminary hypotheses to explain such a common stellar migration but 100,000 stars in still a limited sample. This is only the first evidence that this phenomenon occurs throughout the galaxy but other studies will be made to understand it better. The fourth phase of the SDSS investigation has already begun and will continue until 2020. Many other data collected by the APOGEE spectrograph are already available. The next analyzes will allow to get a bigger picture of what’s happening in the Milky Way.
