Stars

Life cycle of a star

Stars begin as clouds of dust and hydrogen, called nebulas. When they get hot enough they start burning hydrogen and produce energy. This process, called fusion, can last billions of years. When a star runs out of hydrogen the fusion process stops and it starts cooling down.

Most stars become red giants after they have burned away all their hydrogen. The core gets smaller but the temperature increases. The area around the core expands because of the high temperature. When a star gets very big it sometimes explodes. Such an explosion is called a supernova and lasts only for a few days. During this phase stars burn billions of times brighter than they normally do. Sometimes the material of a supernova collapses and turns into a very dense ball of matter called a neutron star. It sends out strong radio waves called pulsars.

Sometimes supernovas have enough energy and mass to collapse inward. They become a black hole. Nothing can escape its gravity and it pulls everything into it. Scientists cannot see a black hole because it has no light. They probably exist in the middle of galaxies.


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Stars