Asymptotic giant branch (AGB) stars are one of the main contributors of the chemical evolution of galaxies, and their ejecta represents an exceptional test for our theoretical knowledge of stellar and nuclear physics.

The planetary nebula shown in the picture is Messier 57, also known as the Ring Nebula. It was formed by the ejection of the outer layers during a very advanced evolutionary phase (phase AGB) of a star with an initial mass between 2 and 3 solar masses.

The Messier 57 Nebula. Credits: Daniele Gasparri

Asymptotic giant branch (AGB) stars are important contributors to the chemical enrichment of our galaxy. In particular, low-mass AGB stars (1.5 < M/M < 3) are one of the main sites of s-process (‘slow’ neutron-capture process), i.e., the neutron-capture nucleosynthesis process mainly responsible for around half of the abundances of the elements heavier than iron in the solar system.

Moreover, the same type of winds that shaped wonderful nebulae like Messier 57, also enriched with newly forged atoms of various elements (some even quite heavy, such as barium and lead) the protosolar nebula from which the Sun and all its planets formed, including the Earth.

References:

Vescovi, D.; Reifarth, R. s-Processing in Asymptotic Giant Branch Stars in the Light of Revised Neutron-Capture Cross Sections. Universe 2021, 7, 239. https://doi.org/10.3390/universe7070239

Nanni, A.; Cristallo, S.; van Loon, J.T.; Groenewegen, M.A.T. Dust Production around Carbon-Rich Stars: The Role of Metallicity. Universe 2021, 7, 233. https://doi.org/10.3390/universe7070233

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