Red-giant branch branch (SB), and red-giant branch (RGB), for stars with different initial masses, all at solar metallicity (Z = 0.02). Also shown are the helium core mass, surface effective temperature, radius, and luminosity at the start and end of the RGB for each star. The end of the red-giant branch is defined to be when core helium ignition takes place. Intermediate-mass stars only lose a small fraction of their mass as main-sequence and subgiant stars, but lose a significant amount of mass as red giants. The mass lost by a star similar to the Sun affects the temperature and luminosity of
Red giant system, if present, uninhabitable, some research suggests that, during the evolution of a star along the red-giant branch, it could harbor a habitable zone for several times 10 years at 2 AU out to around 10 years at 9 AU out, giving perhaps enough time for life to develop on a suitable world. After the red-giant stage, there would for such a star be a habitable zone between 7 and 22 AU for an additional 10 years. Later studies have refined this scenario, showing how for a star the habitable zone lasts from 10 years for a planet with an