The star life-cycle
Stars are born out of a huge, cold cloud of gas and dust called a nebula. The particles are drawn together by gravity and as they grow in size their gravitational energy is is converted into heat energy. This is called a Protostar. For these clumps to begin life as a star they must achieve and maintain equilibrium which is a balance between gravity pulling matter towards the centre and gas pressure pushing heat and light away from the centre. When equilibrium is maintained, the Protostar moves into a phase called the Main Sequence.
The Main Sequence takes up most of the Stars' lifetime. After a star has formed it creates energy at its core through nuclear fusion. The equilibrium allows for a long stable period in the star's lifetime. Over time, the star loses heat and light energy into the universe and slowly contracts causing the star's temperature, density and pressure to increase. As the hydrogen needed for nuclear fusion is used up the star swells and is called a Red Giant. It appears red as the surface cools.
As low mass stars, like our sun, cool their core can't contract enough to begin carbon fusion. There is more gravitational force pulling toward the centre than gas pressure pushing outwards and they collapse. They become White Dwarf Stars composed mostly of carbon and are about the size of our Earth. The White Dwarf surface becomes very hot, but without fuel it begins to cool and eventually fades to become a Black Dwarf Star.
Larger mass stars change as their outer layers collapse into the core. Material collects around the core until there is enough to cause a hydrogen explosion called a Supernova. The dense core left behind after a Supernova is called a Neutron Star. The largest stars become so dense that after a supernova the core collapses in on itself and becomes a Black Hole.
The dust and gas that explodes outwards during a Supernova becomes a nebula. As the star life cycle begins again, the stars that are formed this time are second generation stars. We know there is a difference in second genaration stars because the elements found in them are only made in the final stages of a big star.
The Main Sequence takes up most of the Stars' lifetime. After a star has formed it creates energy at its core through nuclear fusion. The equilibrium allows for a long stable period in the star's lifetime. Over time, the star loses heat and light energy into the universe and slowly contracts causing the star's temperature, density and pressure to increase. As the hydrogen needed for nuclear fusion is used up the star swells and is called a Red Giant. It appears red as the surface cools.
As low mass stars, like our sun, cool their core can't contract enough to begin carbon fusion. There is more gravitational force pulling toward the centre than gas pressure pushing outwards and they collapse. They become White Dwarf Stars composed mostly of carbon and are about the size of our Earth. The White Dwarf surface becomes very hot, but without fuel it begins to cool and eventually fades to become a Black Dwarf Star.
Larger mass stars change as their outer layers collapse into the core. Material collects around the core until there is enough to cause a hydrogen explosion called a Supernova. The dense core left behind after a Supernova is called a Neutron Star. The largest stars become so dense that after a supernova the core collapses in on itself and becomes a Black Hole.
The dust and gas that explodes outwards during a Supernova becomes a nebula. As the star life cycle begins again, the stars that are formed this time are second generation stars. We know there is a difference in second genaration stars because the elements found in them are only made in the final stages of a big star.