Stellar evolution is a fascinating process that begins with the birth of stars. Stars are born within vast clouds of gas and dust called nebulae. These clouds are composed mostly of hydrogen and helium, the two lightest elements in the universe. As these clouds collapse under their own gravity, they heat up and form a protostar. Over time, the protostar continues to accrete more mass from the surrounding cloud, growing larger and hotter until nuclear fusion ignites in its core.
The Life of a Star
Once a star begins nuclear fusion, it enters the main sequence phase of its life cycle. During this phase, the star fuses hydrogen into helium in its core, releasing energy in the form of light and heat. This energy creates an outward pressure that balances the inward pull of gravity, maintaining the star's stability. The length of time a star spends on the main sequence depends on its mass, with more massive stars burning through their fuel more quickly than less massive ones.
The Death of Stars
As a star exhausts its hydrogen fuel, it begins to undergo changes that ultimately lead to its death. For smaller stars like our Sun, this process involves expanding into a red giant and shedding its outer layers to form a planetary nebula. The remaining core collapses to form a white dwarf, a dense stellar remnant that slowly cools over billions of years. In contrast, more massive stars end their lives in spectacular supernova explosions, leaving behind neutron stars or black holes depending on their mass. These remnants continue to influence the evolution of galaxies long after their parent stars have faded away.