Red-giant branch Red-giant branch The red-giant branch (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass stars. Red-giant-branch stars have an inert helium core surrounded by a shell of hydrogen fusing via the CNO cycle. They are K- and M-class stars much larger and more luminous than main-sequence stars of the same temperature. Red giants were identified early in the 20th century when the use of the Hertzsprung–Russell diagram made it clear that there
Gas torus no clear evidence of such a torus. While neutral nitrogen could not be measured, the ions near the orbit of Titan were primarily hydrogen or water group (O, OH, HO and HO) from the Enceladus torus. Trace amounts of nitrogen ions were detected but at levels consistent with an Enceladus source. A fictional gas torus is the setting for Larry Niven's novels "The Integral Trees" and "The Smoke Ring", in which a gas giant in orbit around a neutron star generates a gas torus of sufficient density and free oxygen to support life (including humans). Gas torus A gas torus