Presolar grains allowed astronomers to make significant discoveries about the evolution of AGB stars through precise chemical analyses.
AGB stars, which are very old, low-mass stars, have enriched the interstellar medium with a great variety of chemical elements. They are extremely bright and cold compared to the Sun, allowing for the formation of complex molecules that coalesce into dust grains. These dust grains interact with the star’s light and can carry away stellar gas, resulting in mass loss. AGB stars are indeed characterised by a very strong mass loss, which forms beautiful planetary nebula (such as Messier 57, also known as the Ring Nebula, in the picture below) before leaving their bare hot core that will evolve as a white dwarf.
AGB stars are considered the most efficient producers of dust in the universe and play a significant role in polluting the interstellar medium. Some of these dust grains, known as presolar grains, have been discovered in meteorites on Earth. These granules survived the formation of the Solar System and became trapped in asteroids (i.e. one of the main sites meteorites originate from), and they can now be extracted and analyzed in laboratories. By studying these grains, astronomers have made significant discoveries about the evolution of AGB stars through precise chemical analyses. This ability to analyze pieces of past stars in the laboratory is a remarkable achievement and opportunity for astronomers.
