Life Cycle of the Stars

By: Jake Bears

Life Cycles in Stars and Humans

Stars and Humans have life cycles that are very similar to each other. Humans start out as a fetus, which is the equivalent of the protostar stage in the stars. During these stages they both start to form and take shape. Then stars enter their main sequence, which is like infancy through adulthood in humans. The stars and humans grow and are most productive during this stage. Then they reach middle age or a red giant for stars. They start to lose energy and it is the first step of old age. But both life cycles have to come to an end. When a human is in old age and a star becomes a white dwarf or black hole, it is no longer productive.


The protostar is the starting point of a stars life and it lasts for around 100,000 years. Protostars are normally composed of hydrogen and helium gases and dust particles. Protostars are large celestial bodies formed from the compression of a nebula. They pull in instellar matter, the area of low density between stars that consists of gas (99%) and dust.

Main Sequence

The longest part of a stars life is the main sequence. During this stage the star has reached equilibrium, which is the battle between gas pressure pushing out and gravity pulling in. If a star does not reach equilibrium, it will die. This is similar to homeostasis in humans. When a star has reached Equilibrium, it can then starts nuclear fusion. Fusion is combining two or more objects to create one entity. During the main sequence, stars fuse hydrogen into helium at it's core by nuclear fusion.

Red Giants

Billions of years into the stars life, it begins to run out of hydrogen to fuse into helium. The stars new source of energy becomes the helium that has been fused from hydrogen. The helium goes through nuclear fusion to create heavier elements. The most common ones are carbon, nitrogen and oxygen, but it also creates elements as heavy as iron. Since the star has to be hotter to fuse these elements, the heat cause it to swell, hence the name red giant.

The Death of Stars

A star can become three different things when it dies; a white dwarf, a neutron star, or a black hole. Which ever one it becomes depends on the stars mass before it dies. For the lower mass stars, they will become a white dwarf. For this to happen the stars luminosity, size, and temperature decreases until it is about the size of the earth. This is the most common ending of a stars life because of the amount of stars with lower masses. Bigger stars can die in a more violent episode. The stars outer layers explode into space in an event called a supernova. They blast into space but the very dense core remains as a neutron star. This rapidly spinning ball of neutrons is extremely dense but only about the size of a large city. The rarest death of a star that can happen is becoming a black hole. This only occurs with enormous stars. It begins the same way as a neutron star, a supernova blasts the outer layers into space but the core shrinks to a point, creating an area of infinite density.

The Color of Stars

The color of a star will tell us a lot about it. The main thing that it will tell us is the temperature as we can see in HR diagrams. HR diagrams combine the variables of temperature and luminosity and will help determine what faze of a stars life it is in. Blue stars are the hottest and the red stars are the coolest. Another factor that we have to take into account when looking at the color of a star is the Doppler affect. When a star is moving away from us and we see it as red it is because of red shift and the same when it is moving towards us and we see blue it is because of blue shift. This is because of the different wavelengths caused by the Doppler affect.