Stellar Remnants

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Star Evolution Nebula • The makings of a star • Made of dust and gas. Protostar • A nebula begins to collapse. • Nuclear fusion converts hydrogen to helium. Sequence of Star Birth • As nuclear fusion occurs, the star begins to burn. • This burning changes gravitational energy into heat energy. The main factor to shape a star’s fate is it’s mass. Main Sequence Star • As star is burning, it is known as a main sequence star. • May be main sequence for millions of years (large stars) or billions of years (small and medium stars). • As a main sequence it is burning H and producing He Main Sequence Star • While a main sequence star, there is a battle between gravity and gas pressure Gas pressure from the burning of the star is pushing outward away from the core Gravity is trying to collapse the star Low Mass Stars • When the H has been used up, there is not enough pressure to prevent gravity from collapsing the star and forming a white dwarf Medium Mass Stars • Medium mass stars burn hot enough to use He as a fuel as well as H • Medium mass stars expand to form a red giant when their H is nearly gone • When all of the H & He is used, the star collapses to form a white dwarf High Mass Stars • Massive stars quickly use up their H & He fuel • When the fuel is gone, the star collapses so rapidly that it explodes as a Supernova. The Sun’s Fate • The sun is an adult main sequence star. –What will happen to it in the next 4 billion years? Stellar Remnants White Dwarfs continue to burn very hot and therefore are very bright even though they are very small Stellar Remnants http://www.edwinhubble.com/s Stellar Remnants are what’s left pace_pics/planetary_nebula_IC _418_350.jpg when a star “dies” Planetary Nebula is the burning gas surrounding a white dwarf star http://nssdc.gsfc.nasa.gov/image/ Planetary nebula are associated with astro/hst_stingray_nebula.jpg medium mass stars (i.e. Sun) Planetary nebula neither planets nor nebula Stellar Remnants Black Dwarfs are what’s left when the white dwarf runs out of fuel It is a mass of the heavy elements (i.e. iron) that resulted from nuclear fusion We have never actually observed a black dwarf Stellar Remnants Neutron Stars are extremely dense (1 tsp. has a mass of 100 million tons) and composed entirely of neutrons Neutron stars are thought to be remnants of supernova events Pulsars are remnants of a supernova that radiate short bursts or pulses of radio energy in very regular periods Stellar Remnants Black Holes are massive stars that have collapsed to such a small volume that its gravity prevents the escape of everything, including light We are able to “see” black holes in two ways The gravity of the black hole bends other light passing nearby As matter is pulled into a black hole, becomes very hot and emits X-rays .

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Plasma Physics and Pulsars
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11. Dead Stars
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