Lecture6

# Lecture6 - Stars Stars have a range of intrinsic...

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Stars Stars have a range of intrinsic luminosities and temperatures (colour) Correlations between colour and luminosity tell the story of stellar evolution. Intrinsically faint stars are much more common than bright stars The Solar luminosity is 3.8x10 26 W ¾ This is enough energy to melt a block of ice 1AUx1kmx1km in only 0.1 s. ¾ If the luminosity of the Sun has been approximately constant, the total energy released since its formation would be 4.8x10 43 J. The surface temperature of the sun is about 5700 K ¾ The central temperature is inferred to be much higher: about 10 million K This means the Sun is a fairly ordinary, main sequence star.

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Stellar Structure Gas pressure in the stellar interior opposes gravity to keep the star in equilibrium The equation of hydrostatic equilibrium equates the pressure gradient to the gas density. 2 r GM dr dP r ρ = , where M r is the total mass within radius r . The gas density and enclosed mass are related by the conservation of mass: ρ π 2 4 r dr dM r = The density, pressure and temperature are related by the equation of state, which can usually be approximated as the ideal gas law.
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