Main-Sequence Stars

The main sequence represents the distinctive line of stars going up and left on an HR-Diagram. Main sequence stars are also known as dwarf stars, and our Sun is included in the main sequence. Proxima Centauri, the closest star to the Sun, is a low-mass red dwarf in the main sequence. Sometimes, astronomers divide the main sequence into two portions, the lower being for stars with masses below 1.5 solar masses and the upper being above that mass threshold. Stars below this mass primarily partake in fusing hydrogen atoms together via the proton-proton chain to form helium, which only occurs if the helium atoms in the star's core are hot enough to overcome their electrostatic attraction to one another. In stars above the mass division, the CNO Cycle dominates to form helium from hydrogen. This involves the nuclear fusion of four protons using carbon, nitrogen, and oxygen catalysts to speed up the reaction. This later forms an alpha particle, which is just a stable helium nucleus, along with other products.

Main sequence stars have varying lifetimes depending on their masses. Generally, the more mass a main-sequence star holds, the shorter its life will be as a main-sequence star.