Giant star mass, when on the main sequence, was below approximately , it will never reach the central temperatures necessary to fuse helium. It will therefore remain a hydrogen-fusing red giant until it runs out of hydrogen, at which point it will become a helium white dwarf. According to stellar evolution theory, no star of such low mass can have evolved to that stage within the age of the Universe. In stars above about the core temperature eventually reaches 10 K and helium will begin to fuse to carbon and oxygen in the core by the triple-alpha process. When the core is
Planetary system and B typically rotate very quickly, which makes it very difficult to measure the small Doppler shifts induced by orbiting planets because the spectral lines are very broad. However, this type of massive star eventually evolves into a cooler red giant that rotates more slowly and thus can be measured using the radial-velocity method. A few tens of planets have been found around red giants. Observations using the Spitzer Space Telescope indicate that extremely massive stars of spectral category O, which are much hotter than the Sun, produce a photo-evaporation effect that inhibits planetary formation. When the O-type star goes