Lifecycle of a Star

Key Stage 4

The lifecycle of a star is the set of distinct stages in a stars existence marked by its composition, behaviour and colour.

The stages in the lifecycle of a star depends upon the mass of the star. More massive stars tend to have shorter lives and more violent deaths.

Nebula - A huge cloud of gas and dust stretching across space which collapses due to gravity to form stars.
Protostar - A glowing ball of gas and dust that is not yet hot enough for fusion to occur in its core.
Main Sequence Star - The longest and most stable period of a stars life when the outward pressure caused by fusion of Hydrogen in its core is balanced by the inward pressure caused by gravity.
Red Giant - A star that has run out of Hydrogen for fusion so the pressures are no longer balanced and its core collapses under gravity until the core is hot enough to fuse Helium into more massive elements. During this time the outer layers expand as the star cools but becomes brighter as it becomes much bigger.
White Dwarf - A star which as run out of low mass elements to fuse. There is no more outward pressure due to fusion so the core collapses due to gravity into a ball of Iron and continues to glow for millions of years as it radiates its thermal energy.
Black Dwarf - Once a White Dwarf has cooled enough it will no longer glow and become a Black Dwarf. These stars do not yet exist because the Universe has not existed long enough for White Dwarves to cool.

Nebula - A huge cloud of gas and dust stretching across space which collapses due to gravity to form stars.
Protostar - A glowing ball of gas and dust that is not yet hot enough for fusion to occur in its core.
Main Sequence Star - The longest and most stable period of a stars life when the outward pressure caused by fusion of Hydrogen in its core is balanced by the inward pressure caused by gravity.
Red Super Giant - A massive star that has run out of Hydrogen for fusion so the pressures are no longer balanced and its core collapses under gravity until the core is hot enough to fuse Helium into more massive elements. During this time the outer layers expand as the star cools but becomes brighter as it becomes the largest type of star in the universe.
Supernova - When a massive star runs out of Helium to fuse the core collapses rapidly. Eventually the elements collide with one another and rebound outwards into an explosion known as a Supernova which can be brighter than all the other stars in a galaxy put together.
- Neutron Star - The elements in the core become packed so tightly that all the protons become neutrons and the star becomes one giant atom around 20km across made of only neutrons.
- Black Hole - The most massive stars collapse into a point so small that the gravity becomes so intense that not even light can escape. This is a Black Hole.