Life cycle of a star

• What is a star?

  a mass of gas releasing energy through nuclear fusion
• a star starts with a huge cloud of dust and gas particles in space(nebula)

  • the force of gravity pulls the particles in the cloud closer together
  • the compressed mass of particles forms a protostar
• protostar to star:

  when the volume of gas decreases, its temperature increases enough for fusion to begin, with hydrogen atoms combining to form helium
• Protostar to star 2

  once the fusion process has begun the star becomes stable. We call this the main sequence
• in a main sequence star the gravitational force pulling the star in is equal to the outward pressure produced by nuclear fusion in the core.
• the life of a main sequence star depends on how massive it is.
• a star is at the end of its main sequence when it runs out of hydrogen

  • nuclear fusion slows down and the force of gravity causes the star to contract ( collisions are more frequent= temperature increases)
• what happens to a star after its main sequence depends on its mass