A lifetime is the duration of a thing's existance or usefullness. Stars can have different lengths of lifetime depending on the composition and size of the star. Small and massive stars have different lifecycles illustrated below.
Small stars have nine stages in their lifetimes. Small stars have mass up to one and a half times that of the Suns mass.
Stage 1 – Stars are born in a region of high density Nebula. They condense into a huge glbule of gas and dust and contracts under its own gravity.
Stage 2 – A region of condensing matter begins to heat up and start to glow. This stage forms Protostars. If a protostar contains enough matter the central temperature will reach 15 million degrees centigrade.
Stage 3 – Due to the high temperature, nuclear reaction in which hydrogen fuses to form helium can start.
Stage 4 – The star starts to release energy. This stops the star from contracting even more and causes it to shine. The star is now called the Main Sequence Star.
Stage 5 – A star of one solar mass remains in main sequence for about 10 billion years until all of the hydrogen has fused to form helium.
Stage 6 – The helium core now starts to contract and reactions begin to occur in the shell around the core of the star.
Stage 7 – The core is hot enough for the helium to fuse to form carbon. The outer layer of the star begins to expand, cool and shine less brightly. The expanding star is now called a Red Giant.
Stage 8 – The helium core finally runs out. The outer layer will begin to drift away from the core as a gaseous shell. The gas that surrounds the core is called Planetary Nebula.
Stage 9 – The core becomes a White Dwarf and the star eventually cools and dims. When it stops shining, the star is dead and called a Black Dwarf.
Massive stars have five stars in their lifetime. Massive stars are categorized by the fact they are three times larger than the Sun. Some massive stars are up to fifty times larger than the sun.
Stage 1 – Massive stars evolve in a similar way to a small stars until it reaches its main sequence stage. The star shines steadily until the hydrogen has fused to form helium.
Stage 2 – The star then becomes a Red Supergiant and starts off with a helium core surrounded by a shell of cooling and expanding gas.
Stage 3 – A series of nuclear reactions occur forming different elements in the shell around the iron core. This takes approximately one million years.
Stage 4 – The core collapses in less than a second. This causes an explosion called a Supernova. A Supernova is a shack wave that blows the outer layer off the star.
Stage 5 – Sometimes the core will survive. If the core does survive it becomes a tiny and dense Neutron Star. If the core is greater than three solar masses the core contracts to become a Black Hole.