What factors determine the lifespan of a star?

The lifespan of a star is determined by its mass, composition, and nuclear fusion reactions.

Stars are born from clouds of gas and dust called nebulae. The mass of a star is the most important factor in determining its lifespan. The more massive a star, the hotter and brighter it is, and the faster it burns through its fuel. This means that more massive stars have shorter lifespans than less massive ones.

The composition of a star also plays a role in its lifespan. Stars are primarily made up of hydrogen and helium, but they also contain small amounts of other elements. The more heavy elements a star has, the faster it burns through its fuel and the shorter its lifespan.

Nuclear fusion reactions are the process by which stars generate energy. The type of fusion reaction that occurs in a star depends on its mass and composition. The most common fusion reaction is the fusion of hydrogen into helium. As a star runs out of hydrogen fuel, it will begin to fuse heavier elements, such as helium, carbon, and oxygen. Each fusion reaction releases less energy than the previous one, which means that the star's energy output decreases over time.

Eventually, a star will run out of fuel and will no longer be able to generate enough energy to counteract the force of gravity. The star will then collapse in on itself, either becoming a white dwarf, a neutron star, or a black hole, depending on its mass.

In summary, the lifespan of a star is determined by its mass, composition, and nuclear fusion reactions. The more massive a star and the more heavy elements it contains, the shorter its lifespan. As a star runs out of fuel, it will eventually collapse and become a white dwarf, neutron star, or black hole.