8/9/2019 Slayton. Astronomy Project Summary Paper

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Life Cycle of a SunBy Asa Slayton

andMegan Decker

Stars form when interstellar gas collapse under the influence of gravity. During a stars lifetime it passes through a series of stages, with a sequence and timingdepending on the mass of the star. As a star passes through these stages, different elements are created depending on the stars mass. When stars are complete, they shed theirmaterial back into the interstellar medium, improving the matter from which future generations of stars will form.

Stars form from cold interstellar clouds. The colder a cloud is the less resistant it is to gravitational collapse. After the clouds are formed protostars begin to form. If thecloud is over a certain mass, and it experiences a gravitational pull, it will begin to collapse. As this happens it will fragment into smaller parts of differing size and mass.These fragmented cloud sections become protostars. Then the temperature and pressure rise. The protostar continues to collapse, and the central temperature and pressure rise.The temperature and pressure levels depend on the mass of the fragment -the higher the mass, the higher the temperature and pressure. If a protostar is less than 0.08 solarmasses, the pressure and temperature at the core do not get high enough for nuclear reactions to begin. Instead of going through the rest of the cycle the protostar becomes abrown dwarf.

After the pressure and temperature rise comes the Stellar Adolescence. The gas that contracts to make a protostar starts to rotate slowly and speeds up as it is pulledinward, creating a disk of stellar material. Before the main sequence, the protostar exhibits unstable behavior such as rapid rotation and strong winds.

Now the star has reached the main sequence. For protostars with more than about 0.08 solar masses, the pressure and temperature within become high enough fornuclear reactions to start. The pressure balances gravity and the protostar becomes a star. Next comes the formation of orbiting planets. Once a star is on the main sequenceand stable, any disk of remaining material will start to cool. As it cools, elements condense out and begin to stick together. The larger clumps attract the smaller ones, untilconglomerations are planet-sized.

Stars spend the greatest proportion of their lives in the main sequence. The more massive a star is, the shorter the period of time it will spend on the main sequence, sincelarger stars burn their fuel at a faster rate than smaller ones. Next stars can become like a sun. When a Sun-like star exhausts the hydrogen in its core, hydrogen-shell burningbegins and it becomes a red giant, often losing its outer layers to produce a planetary nebula. It eventually collapses, and the temperature and pressure at its core initiatehelium-core burning. The star again expands as helium-shell burning occurs, before finally collapsing to become a white dwarf that gradually fades to become a black dwarf.

Picture URLs

http://www.tqnyc.org/2006/NYC063368/redgiant.jpg

https://reader010.{domain}/reader010/html5/0601/5b1051d240e4a/5b1051d43b63f.jpg

https://reader010.{domain}/reader010/html5/0601/5b1051d240e4a/5b1051d48a12f.jpg