Giants, Supergiants and Hypergiants

Observing the stars in our night sky tells us that giant, supergiant and hypergiant stars hold an unique importance in the understanding of stellar populations. Theoretical stellar models predict a rich tapestry of evolved stars. These evolved stars result in supernova explosions for massive stars and the shedding of the outer layers of low- and intermediate-mass stars to form white dwarf stars. Stars on these pathways provide elemental and kinematic feedback that shapes their host galaxies and synthesize the elements that we observe in the Universe today. Observational surveys in the Milky Way and the Local Group of galaxies shape our physical understanding of stellar evolution. Hypergiant stars represent stellar evolution at the extremes, displaying evidence of intense stellar winds combined with luminosities and radii that are unrivalled. Supergiant stars are used as elemental beacons in distant galaxies, and supergiants that cross the Cepheid variable instability strip can be used as rulers to measure the scale of our Universe. The overwhelming majority of stars in the Milky Way will become giant stars. Giants are hundreds of times larger and thousands of times more luminous than the Sun, which makes them excellent tracers of stellar structure. In this chapter, I describe the observational and theoretical manifestations of stellar evolution at various stages and masses. I highlight evolutionary connections between evolved products and comment on their eventual endpoints.