My topic is life cycle of stars.
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Birth: When a star is born its first created by the effects of a nebula. A nebula is nothing but gas and dust. The gravity of the nubula smashes the gas and dust together and forms a protostar. A protostar is 97% hydrogen and 3% helium from the nebula and as the star's atoms increase in number in grows hotter til it is a full grown star.
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Life: As the contraction of the gas and dust progresses and the tempature reaches 15 million degrees or so, the pressure at the center of the ball becomes enourmous. The electrons are stripped off of their parent atoms, creating plasma. The contraction continues and the nuclei in the plasma start moving faster and faster. Eventually, they approach each other so fast that they overcome the electrical repulsion that exists between their protons. The nulei crash into each other so hard that they stick together, or fuse. In doing so, they give off a great deal of energy. This energy from pours out from the core, setting up an outward pressure in the gas around it that balances the inward pull of gravity. When the released energy reaches the outer layers of the ball of gas and dust, it moves off into spaces in the form of electromagnetic radiation. The ball, now a star, begins to shine. New stars come in a variety of sizes and colors. They range from blue to red, from less than half the size of our Sun to over 20 times the Sun's size. It all depends on how much gas and dust is collectes during the stars formation. The color of the star depends on the surface temperature of the star. The more mass a star stars out with, the brighter and hotter it will be. For a star, everything depends on its mass. Throughout their lives, stars fight the inward pull of the force of gravity. It is only the outward pressure created by the nuclear reactions pushing away from the star's core that keeps the star "intact". But these nuclear reactions require fuel, in particular hydrogen. Eventually the supply of hydrogen runs out and the star begins its demise. Cores of stars at least half as massive as the sun, however, will eventually collapse and heat enough to start burning helium in their cores. Once helium-burning starts, the star decends the giant branch again, reverses its swelling a bit, and lives happy fusing helium in its core, and hydrogen in a sgell around the core. then the giant dance begins again. The core helium runs out, and the star once again becomes a red giant. Stars like the sun get off the bus here, and become planetary nebulae and white dwarfs.
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End: After millions to billions of years, depending on their initial masses, stars run out of their main fuel - hydrogen. Once the ready supply of hydrogen in the core is gone, nuclear processes occuring there cease. Without the outward pressure generated from these reactions to counteract the force of gravity, the outer layers of the star begin to collapse inward toward the core. Just as during formation, when the material contracts, the tempature and pressure increase. This newly generated heat temporarily counteracts the force of gravity, and the outer layers of the star are now pushed outward.BH1m.jpg