A low-mass star has a mass between about 0.5 and 10 solar masses. The Sun is a low-mass star.When most of the hydrogen in the core has been fused into helium, fusion in the core slows and the radiation pressure falls. Gravity makes the core contract and heat up. This heat starts hydrogen fusion in a shell around the core, and the outer layers of the star expand and cool. The star becomes a red giant: very large, with a cool (red) surface but a high luminosity.
The core keeps contracting until it is hot enough (about 108 K) for helium nuclei to fuse into carbon and oxygen.When the helium in the core runs out, a low-mass star's core cannot get hot enough to fuse carbon. The outer layers drift away into space, forming a glowing shell of gas called a planetary nebula. Despite the name, it has nothing to do with planets.The hot, dense core that is left behind is a white dwarf. No fusion happens in a white dwarf. It glows only because it is still very hot, and it slowly cools and fades over billions of years.The life cycle of a low-mass star is:protostar → main sequence star → red giant → planetary nebula + white dwarf
The core keeps contracting until it is hot enough (about 108 K) for helium nuclei to fuse into carbon and oxygen.When the helium in the core runs out, a low-mass star's core cannot get hot enough to fuse carbon. The outer layers drift away into space, forming a glowing shell of gas called a planetary nebula. Despite the name, it has nothing to do with planets.The hot, dense core that is left behind is a white dwarf. No fusion happens in a white dwarf. It glows only because it is still very hot, and it slowly cools and fades over billions of years.The life cycle of a low-mass star is: