Red giant brightness so common on both types of stars. Red giants are evolved from main-sequence stars with masses in the range from about to around . When a star initially forms from a collapsing molecular cloud in the interstellar medium, it contains primarily hydrogen and helium, with trace amounts of "metals" (in stellar structure, this simply refers to "any" element that is not hydrogen or helium i.e. atomic number greater than 2). These elements are all uniformly mixed throughout the star. The star reaches the main sequence when the core reaches a temperature high enough to begin fusing hydrogen (a few
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