1. Nebula

• All stars form from a giant cloud of?hydrogen gas?and?dust?called a?nebula

2. Protostar

• The force of?gravity?within a nebula pulls the particles?closer together?until it forms a hot ball of gas, known as a?protostar
• As the particles are pulled closer together the?density?of the protostar will?increase
  • This will result in?more frequent collisions?between the particles which causes the?temperature?to?increase

   

3. Main Sequence Star

• Once the protostar becomes hot enough,?nuclear fusion? reactions occur within its core
  • The?hydrogen?nuclei will fuse to form?helium?nuclei
  • Every fusion reaction releases?heat?(and light) energy which keeps the core hot

   

• Thermal expansion from?fusion?reactions occur within its core due to fusion and the force of gravity keeps the star in equilibrium
• At this point, the star is born, and it becomes a?main-sequence star
• During the main sequence, the star is in?equilibrium?and?said to be?stable
  • The?inward force?due to?gravity?is?equal?to the?outward pressure force?which results from the expanding hot gases inside the star

   

4. Red Giant

• After several billion years the hydrogen causing the fusion reactions in the star will begin to run out
• Once this happens, the fusion reactions in the core will start to?die down
• This causes the core to?shrink?and?heat?up
  • The core will shrink because the inward force due to gravity will become?greater?than the outward force due to the pressure dies down

   

• A new series of reactions will then occur around the core, for example,?helium?nuclei will undergo?fusion?to form?beryllium
• As the core shrinks, more reactions will cause the outer part of the star to?expand
• It will become a?red giant
  • It is red because the?outer surface?starts to?cool

   

5. White Dwarf

• The star will eventually become?unstable?and eject the outer layer of dust and gas
• The core which is left behind will?collapse completely, due to the pull of?gravity, and the star will become a?white dwarf
• The white dwarf will be?cooling?down and as a result, the amount of?energy?it emits will?decrease

The lifecycle of a solar mass star