Lithium as a Probe of Stellar and Galactic Physics

Lithium plays a unique role in astrophysics, as it is a powerful diagnostic for the physics and evolution of low-mass stars, Galactic archaeology, and cosmology. We review the Li observations in stars at different phases of their evolution, the strengths and the limitations of the current theoretical stellar models to explain the Li abundance data, and our understanding of the Li sources and of the evolution of Li throughout the Galactic history. Key takeaways from the current state of the research in the field include the following: ▪ Stellar evolution models accounting for fundamental transport processes of chemical species and angular momentum hold the promise of providing a common “stellar Li depletion” explanation to the Li abundance patterns observed in all Galactic stellar populations, including the “dip” and the “plateau(s).” ▪ Novae are most probably the main source of Li in the Galaxy, on observational (but not yet theoretically established) grounds. ▪ Radial migration of stars in the Galactic disk holds the key to understanding many aspects of the Li evolution in the Milky Way.