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Stars A Star is an object that produces energy at its core! A mass of plasma held together by its own gravity; Energy is released as electromagnetic radiation! Stars differ in size, age and temperature. Star Power Stars are powered by nuclear fusion • At 15 million degrees Celsius in the center of the star, fusion occurs. • Very simplified: 4 Hydrogen 1 Helium + energy! E= 2 mc Nuclear fusion • Fusion makes LOTS of energy • E = mc2 What do E and M symbolize? E = Energy and m = mass ….and “c”….? c = the speed of light (300,000,000 m/s) • Astronomers learn about stars by studying their luminosity, spectrum, and motion Life Cycle of the Stars Stars are formed, changed, and recycled! Stars • A celestial body of hot gases that radiates energy from nuclear fusion occurring at the core. Milky Way, Nebula NGC 3603 20,000 light years away http://news.nationalgeographic.com/news/2007/10/images/071002-star-picture_big.jpg _______ Light Year _____ is the distance light can travel in ONE YEAR. Light travels at a speed of 300,000,000 meters/second. Milky Way, NGC 3949, 50 million light years In one Second, light can travel around the Earth 10 times, according to one estimate. 9,400,000,000,000,000 meters 9 quadrillion (9 thousand billion) http://www.nasa.gov/multimedia/imagegallery/image_feature_202.html http://www.nasa.gov/multimedia/imagegallery/image_feature_73.htm l http://www.nasa.gov/mission_pages/spitzer/news/spitzer20070212.html ____________: NEBULA A dense cloud of gas and dust; the birthplace of stars. Horesehead Nebula; 1500 light years distant Bubble Nebula Stingray Nebula Horsehead Nebula Red Square Nebula Crab Nebula Eye (of God) Nebula Southern Crab Nebula Eskimo Nebula The nebula begins to contract due to __________. GRAVITY The pressure and temperature increase as a PROTOSTAR is formed. _____________ When the temperature gets hot FUSION enough, _______________ begins andMAIN a _______ ____________ star is SEQUENCE born. Nuclear Fusion: The process of taking atom centers ( the nucleus) and fusing them together. A Balancing Act • Energy released from nuclear fusion counter-acts inward force of gravity. Throughout its life, these two forces determine the stages of a star’s life. MASS A star loses ____________ during fusion as energy is released. This decreases the star’s gravity. A star will expand, becoming a _______________. RED GIANT Very massive stars become ________ _____ GIANTS _________. SUPER RED http://www.daviddarling.info/images/red_giant.gif http://www.universetoday.com/2008/01/31/will-earth-survive-when-the-sun-becomes-a-red-giant/ As the fuel runs out in a average sized star, fusion _________ slows down. The star will shrink in size, becoming a White _________ _______. Dwarf PULSAR A ____________ is a rotating white dwarf emitting radio waves. Small and medium stars cool and stop producing energy. We then call them ___________________. BLACK DWARVES http://chandra.harvard.edu/photo/2004/rxj1242/index.html http://www2.ph.ed.ac.uk/nuclear/photo/ A ___________________ SUPERNOVA is an explosion _____________ that marks the end of a very massive star’s life. When it occurs, the exploding star can outshine all of the other stars in the galaxy in total for several days and may leave behind only a crushed core. Discovered by 14 year old Catherine Moore, on Nov. 7 2008. 1987 Supernova Large Magellanic Cloud 160,000 light years away Larger stars supernovae and form __________________. http://chandra.harvard.edu/photo/2004/rxj1242/index.html http://www2.ph.ed.ac.uk/nuclear/photo/ The most massive stars supernovae and form _________________ BLACK HOLES A black hole is an extremely massive remnant from which light can not escape. “Black holes are where God divided by zero” Stephen Wright The Largest stars are red supergiants, 1500 times our sun. The smallest are red dwarfs, not much larger than Jupiter. What makes some stars appear brighter? • LUMINOSITY refers to the brightness of stars. Because some stars are CLOSER or BIGGER, they may seem more luminous. What makes some stars appear different colors? • The temperature affects the color. The hottest stars are blue, while the coolest stars are red. Blue > 30,000 Kelvin Blue to blue white 10,000 -> 30,000 Kelvin White 7,500 -> 10,000 Kelvin Yellowish White 6,000 -> 7,500 Kelvin Yellow 5,200 -> 6,000 Kelvin Orange 3,700 -> 5,200 Kelvin Red 1,000 < 3,700 Kelvin Brown < 1,000 Kelvin Black 0 Kelvin H-R diagram http://www.cosmosportal.eu/cosmos/tr/node/56058 Do larger stars or smaller stars last longer? Do hot stars or cool stars last longer? Large, more massive stars have much more _____________ than the sun. This greater internal gravity pressure causes fusion reactions to occur quickly __________. This causes the largest stars to burn their fuel, and eventually run out, much more ______________. quickly Larger stars live ___________ lives. shorter Bigger stars are brighter and hotter due to the rapid fusion rate of __________. All stars spend the majority of their lives hydrogen fusing __________ into helium ________________: the main sequence. hydrogen in the central When all of the _____________ regions is converted to helium, the star will begin to “burn” helium into _______________. carbon Stars heavier than about 5 times the mass of the ______ can do this with no problem: they burn hydrogen helium _____________, and then _______________, and oxygen carbon then _____________, _______________, silicon, and so on…until Iron. Iron is the lightest element that doesn’t energy when you attempt to release __________ fuse it together. You actually end up with less energy than you started with! So instead of generating pressure to hold up the outer layers, the iron fusion actually takes it out of the core. Thus, there is nothing left to combat gravity from the outer layers. ________________ supernova The result: ___________! Iron collapse This implosion (___________) happens very, very quickly: about 15 seconds. During the collapse, the nuclei in the outer parts of the star are pushed together, so close that elements heavier than __________ Iron are formed. Apparent Magnitude: How bright an object appears from Earth. Absolute Magnitude: How bright an object would appear from 32.6 light years away. Low numbers are brighter. Negative numbers are extremely bright. The End.