The average star cycle: nebula, protostar, main sequence, red giant, white dwarf. The massive star cycle: nebula, protostar, main sequence, super red giant, supernova, black hole, neutron star.

The star cycle is the sequence of changes that a star undergoes throughout its existence.

<h3>The evolutive stages of an<u> average star</u> are </h3>

Nebula: Stars are born from the nebula that is the dust and gas particles condensation due to gravity effect in the interstellar clouds

Protostar: It is a more advanced level of condensation.

Main sequence. Equilibrium between gravity and nuclear fusion helps the star keep stable as long as the fuel lasts. The two main types are

• <em>Orange dwarf</em><em>: </em>between the red dwarf and the yellow dwarf

• <em>Yellow dwarf:</em> Like the sun

Subgiant: occurs when orange and yellow dwarfs finish their main sequence and start to run out of fuel, expanding.

Red giant. After the subgiant stage, the star enters a giant phase. The star can reach a size of up to 100 times its current size.

White dwarf. When average-sized stars run out of fuel, the red giant begins to disintegrate, losing its outer layers and exposing its core, which will become a white dwarf.

<h3>The evolutive stages of a<u> </u><u>giant star</u><u> </u>are </h3>

Nebula

Protostar

Main sequence. There are two main types

• <em>Yellow supergiant</em>. Extremely short phase. Almost no stars are known to be in this stage. The star swells on its way to becoming a red supergiant.

• <em>Red supergiants</em> are the largest stars in volume, but not in mass.

Supernova. When fuel is over in the red supergiants, the gravitational collapse produces a violent explosion originating the supernova.