There is a life cycle of stars. Stars are born, they live and mature, and then they die. Our sun is a star and it is approaching the middle of its life cycle. As it gets older it will turn into a red giant. Life on earth will not be possible when that happens. The sun will expand until its core turns into a white dwarf. The outer layers of the sun will become a planetary nebula. And, our solar system will no longer exist.
Start of the Life Cycle of Stars
Stars are born in regions of space with clouds of hydrogen gas and dust. These regions are called nebulae. The life cycle of stars begin in these nebulae. Gravitational attraction of the gases and dust gradually cause these clouds to condense. The clouds begin to collapse into a ball which spins more and more rapidly. Pressures begin to build and the temperature of the ball of gas begins to rise. This ball is known as a protostar.
When the temperature of the gas ball is high enough, nuclear fusion begins. Fusion is the combining of hydrogen atoms into a helium atom. Nuclear fusion releases tremendous amounts of energy. Once fusion begins, a star is born.
Young Stars and Main Sequence
A newly formed star obtains its energy from fusion. This energy creates surface temperatures that vary from 2,000° Centigrade to more than 30,000° Centigrade. The hottest stars are blue-white in color. The cooler stars are red in color.
These stars are now in a stage called main sequence. Fusion creates energy that creates pressure. This pressure pushes the star's gases outward to space. At the same time, stars are giving off energy in the form of light and heat. This results in the gradual loss of materials from the star. The loss then results in a gradual contraction of the star from gravity. A main sequence star is in a balance between pressure pushing outwards and gravitational contraction pulling inwards.
As the star continues to consume its hydrogen it will reach a point when there is none left. Without fusion, the star is no longer in a balance. Without outward pressures, the star begins to collapse and enters another stage in the life cycle of stars.
Older Stars and Death
Older stars begin to collapse when the star runs out of its hydrogen fuel. The core of the star is mostly helium at this stage. As the star begins to collapse, tremendous pressures are created. These presures force helium to now begin a new type of fusion reaction. This time the helium fuses into heavier materials such as carbon.
The pressures from the helium fusion reaction push outward. The star begins to expand into a much larger star than it was before. At this stage, the star becomes a red giant. This is just a temporary phase in the life cycle of stars.
Red giants can be over a hundred times larger than our sun. They are bright but have a lower temperature than a main sequence star.
For stars with a smaller mass than our sun, the red giant expands and loses its outer layers. The remaining core shrinks and becomes a white dwarf star. The outer layers become planetary nebulae. The white dwarf continues to cool slowly until it has no more energy. The dwarf star becomes a black dwarf star in the life cycle of stars.
Stars with a much larger mass than our sun will experience a violent explosion. Instead of becoming a dwarf star, they explode and are destroyed. This explosion of the star is called a supernova. A supernova will create a neutron star. The neutron star is a very small, dense and made up of neutrons.
If the mass of the neutron star is great enough, it will become a black hole. Although very small, the mass of the black hole is very high. This creates a very strong gravitational pull. The pull is so great that all nearby matter and light are pulled into the black hole.
(photo credits: Clearviewstock)
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