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The Life Cycle of Stars

Low Mass vs. High Mass

Holly Cordray

on 4 November 2012

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Transcript of The Life Cycle of Stars

The Life Cycle of Stars: Low Mass vs. High Mass Low Mass: High Mass: Bibliography: http://www.nasa.gov/images/content/57329main_MM_image_feature_151_jwfull.jpg http://2.bp.blogspot.com/-xAZLQ4Y1-Ak/ToHtwLGBHaI/AAAAAAAAACM/il-nSSbq-iU/s1600/protostar-440x339.jpg http://www.williamsclass.com/EighthScienceWork/ImagesEighth/Sun-MainSequence.jpg http://static.guim.co.uk/sys-images/Arts/Arts_/site_furniture/2007/06/11/catseyenebula460.jpg http://www.portaltotheuniverse.org/static/archives/posts/feature/post-118898.jpg http://ucsdnews.ucsd.edu/graphics/images/2006/neutron-star-jet_bg.jpg http://www.bibliotecapleyades.net/imagenes_universo/black_hole_4.jpg http://legalknowledgecenter.files.wordpress.com/2012/06/supernova.jpg http://www.dailygalaxy.com/.a/6a00d8341bf7f753ef014e88606119970d-500wi http://www.passmyexams.co.uk/GCSE/physics/images/stars-life-red-giant.jpg Nebulae are clouds of dust and gas. They are mainly composed of hydrogen. However, nebulae include other matter, helium being the secondary component. Many stars can be formed from a single nebula. Nebulae Protostars form from nebulae. The hydrogen in the nebula is eventually forced by gravity to compact and spin. As the matter spins, it increases in temperature, and becomes a protostar. Protostars Stars remain in the main sequence stage for much of their lives. Protostars continue to heat up to fifteen million degrees Celsius, at which point nuclear fusion takes place in the core of the star. It contracts, shines brightly, and stabilizes. For low mass stars, this stage could last up to ten billion years; for high mass stars, the stage's duration is one million to twenty million years. Also, the size of high mass stars in their main sequence is greater than that of low mass stars. Our sun is approximately halfway through this stage. Main Sequence http://imagine.gsfc.nasa.gov/docs/teachers/lessons/xray_spectra/background-lifecycles.html The red supergiant phase ends when a supernova occurs. Once the supergiant runs out of helium, there is enough heat to fuse carbon into a succession of increasingly massive elements until iron is formed. As iron absorbs energy, it causes the force of gravity to become greater than the outward-pushing force and the star collapses. The collapse results in iron being fused into heavier metals, and the subsequent energy release causes the explosion of the star. The supernova happens over the course of several months. Supernovae Stars with a solar mass of ten or greater eventually become red supergiants. They are vastly greater in size than their low-mass counterparts. The duration of this phase, like their overall lifespans, is shorter for red supergiants than red giants. Red Supergiants Stars in the main sequence stage maintain a constant process of nuclear fusion by converting hydrogen into helium. Once the star runs out of hydrogen, it must start fusing helium into carbon. The forces acting upon it (gravity pushing in, nuclear power pushing out) become unbalanced, because the force of gravity is overwhelmed by the fusion of elements more massive than hydrogen. This causes the core to contract and the outer shell to expand. The shell cools and becomes red; the color indicates a lower temperature. Red Giants A planetary nebula is formed after the red giant phase. When the core of the star collapses, the red outer shell is expelled. The formation that this leaves is called the planetary nebula, and is like a disc in appearance. Planetary Nebulae The core of the star, left within the center of the planetary nebula, becomes a dwarf. This remnant of the star is still extremely hot, so it is white in color. White Dwarfs A black hole is formed if the initial solar mass of the star was greater than thirty. In essence, the star is collapsing continually and infinitely. Black holes emit no light, so are completely dark, and they are spherical. They have such a strong gravitational force that any objects passing nearby (including stars and even light) are pulled into them. Black Holes After the explosion, if the solar mass of the star initially was between ten and thirty, a neutron star is formed. Neutron stars are minimal in size, yet are incredibly dense: one teaspoon worth of a neutron star weighs a million tons! This density is due to the combination of protons and electrons during the final collapse of the star. Neutron Stars http://www.daviddarling.info/images/black_dwarf.jpg As the star dies, it fades. The white dwarf gradually decreases in temperature and color. Eventually it becomes brown, then black, as the light radiating from it dims, then ceases altogether. Black Dwarfs
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