How is a star's life cycle determined?

Answer 1

Largely by it's size and color. To keep it simple, if all stars were the same size, blue and blue/white stars would be the youngest, white stars next, then yellow stars (middle aged, like our Sun) and red stars. But size also figures into it. A medium sized blue star has a long life ahead of it. A very big blue star will have a shorter life: Bigger "engine", faster "speed", sooner "breakdown", basically. Stars begin life as mostly hydrogen. Their size creates tremendous pressure in their centers which converts the hydrogen to helium, creating as a by-product tremendous heat. As the hydrogen becomes used up, the star cools somewhat and expands - getting larger and redder. Old Age, as it were. This is all very simplified, but it gives you the general picture. Astronomers classify stars as type O (hottest) through B, A, F, G, K, and M, with many subcategories within those! Our sun is an utterly ordinary type K star, about halfway through it's expected lifetime of 8-9 billion years right now.

Answer 2

A star's life cycle is determined by its mass. Higher mass stars have shorter life spans due to the increased nuclear fusion reactions happening in their cores, leading to faster consumption of fuel. Lower mass stars, like our Sun, have longer life spans, gradually fusing hydrogen into helium over billions of years. The life cycle of a star involves stages such as nebula, main sequence, red giant or supergiant, and can end as a white dwarf, neutron star, or black hole depending on its mass.