Frequently asked in the IGCSE exam 👍
Life Cycle of Stars
Formation of Star
- Dust and gas clouds exist as a form called nebula in the galaxy. The nebula is mostly composed of hydrogen.
- The gravitational attraction between these dust and gas brings them together, forming a protostar.
- As the clouds become more concentrated, the temperature and pressure increase to an extent that fusion of hydrogen nuclei to make helium nuclei becomes possible.
- During the fusion process, a lot of radiation energy is released. This energy tends to expand the star, while the gravitational attraction tends to collapse the star.
- A star is formed when an equilibrium is reached between these two forces, and the gravitational attraction is equal to the radiation pressure from the fusion.
Evolution of Average Mass Star
- When the star uses up all of its hydrogen fuel for fusion reaction, it starts to fuse heavier elements.The star then swells to a red giant star.
- When all the reactions are over, the star contracts due to gravitational pull and cools into a white dwarf.
Evolution of Large Mass Star
- It will first undergo a similar process as an average mass star, fusing heavier elements and swelling to a red super giant star.
- Since a large star can continue on with the nuclear reaction, the fusion reaction will go on until the star becomes too hot and expands. When the star cannot sustain itself anymore, it will explode as a supernova.
- Either a neutron star or black hole is left behind.