The Life Cycle of a Star

Topics: Star, White dwarf, Supernova Pages: 1 (289 words) Published: March 16, 2013
Part 7
The life cycle of a star
How does gravity, nuclear fusion and mass affect the life cycle of a different sized stars? * Stars initially form from clouds of dust and gas. The force of gravity makes the gas and dust spiral in together to form a protostar. Gravitational energy has converted into heat energy, so the temperature rises * When the temperature gets high enough, hydrogen nucli undergo thermonuclear fusion to form helium nuclei and give out massive amounts of heat and light. A star is born. It immediately enters a long stable period where the heat created by the nuclear fusion provides an outwards pressure to balance the force of gravity pulling everything inwards. In this stable period it`s called a MAIN SEQUENCE STAR and it typically lasts several billion years * Eventually the hydrogen begins to run out and the star then swells into a RED GIANT (it becomes red because the surface cools). A small-to-medium-sized star like the sun then becomes unstable and ejects its outer layer of dust and gas as a planetary nebula * This leaves behind a hot, dense solid core- a WHITE DWARF which just cools down and eventually fades away (That`s going to be really sad). * Big stars ,however, form red supergiants- they start to glow brightly again as they undergo more fusion and expand and contract several times, forming heavier elements in various nuclear reactions. Eventually they`ll explode in a SUPERNOVA * The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a NEUTRON STAR. If the star is big enough this will become a BLACK HOLE How can we explain the theory that we are all made of “star
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