Most stars we see are on the main sequence. Stars spend most of their lives consuming their initial stock of hydrogen. Is there a connection between these two statements? If so, what is it?
Yes, there is a connection between these two statements. The main sequence is a region on the Hertzsprung-Russell (HR) diagram where most stars are located. It represents a stable stage in the life cycle of a star, during which it spends the majority of its lifetime.
Stars on the main sequence, including our Sun, generate energy through nuclear fusion in their cores. The primary fuel for this fusion process is hydrogen, which gets converted into helium. This process releases an enormous amount of energy in the form of light and heat, which allows the star to shine.
As stars consume their initial stock of hydrogen, they gradually exhaust this fuel in their cores over billions of years. The rate at which a star consumes hydrogen depends on its mass. More massive stars burn through their hydrogen more rapidly than lower-mass stars.
Once a star has exhausted its hydrogen fuel, it undergoes changes in its structure and evolves into a different phase, depending on its mass. This might include expanding into a red giant or contracting into a white dwarf, among other possibilities. But during their main sequence phase, stars remain relatively stable and maintain a consistent size, temperature, and luminosity.
Therefore, the connection between the two statements is that the majority of stars we observe are on the main sequence because they spend the majority of their lives consuming their initial stock of hydrogen, releasing energy through nuclear fusion.