How is Betelgeuse built?

Answer 1

Stars are formed when hydrogen molecular clouds collapse. The Sun, for example, is halfway through its main sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. Stars without the mass to explode will enter the red giant phase, in which its outer layers expand as the hydrogen fuel in the core is consumed and the core contracts and heats up. Stars with more than about 10 solar masses after burning their hydrogen become red supergiants during their helium-burning phase. Betelgeuse is one such red supergiant and has formed in the same way.