Star Clusters - o Star is Born • Once nuclear reaction...

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Star Clusters Star clusters are the oldest objects in the universe look at stars having many different ages to get the life history of a typical stars o Clouds of gas and dust o if cloud is dense enough, its own self-gravity causes it to contract o Clout fragments into smaller parts known as protostars – they are in free-fall- so little gas that theres no collisions – slow gradual process As the density grows, collisions among particles cause the gas to heat up pressure rises and the contraction slows down Temperature and Pressure Rise need nuclear reactions to occur for a star to form o Pre-main-sequence star relatively slow gravitational contraction Gravitational energy is still being released Gas heats up and eventually heats up enough (10 million K) to get nuclear reactions
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Unformatted text preview: o Star is Born • Once nuclear reaction begins, gravitational energy stops acting as the primary force o Contraction Ceases Star’s L and T don’t change much during main-sequence lifetime • Contracting pre-main-sequence star = Gravitational Energy • Star – Nuclear Energy • Mechanical balance: “hydrostatic equilibrium” = Stable o gravity exerted and the pressure from inside are equal • Brown Dwarf – no long-term fusion o fusion occurs for a short time o not hot enough to fuse hydrogen, deuterium fusion does occur though o held up by degeneracy pressure o faintly glow at infrared wavelengths • Center of a star has a very high temperature o Hydrogen atomrs are fully ionized to protons o nuclear fusion produces energy...
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This note was uploaded on 04/04/2008 for the course ASTRO C 10 taught by Professor Filippenko during the Fall '08 term at Berkeley.

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