When a star like our Sun no longer has any hydrogen or heliumfuel for reactions

Question

When a star like our Sun no longer has any hydrogen or heliumfuel for reactions in its core, it can colla[se and become a whitedwarf star. Often the star will blow off its outer layers and losesome mass before it collapses into a rapidly spinning, white dwarfstar. Suppose a star with mass 1Msun with radius 6.96 x108m and rotating once every 25 days becomes a whitedwarf with a mass of .6Msun and a rotation period of131s. A) What is the radius of the white dwarf (It isspherical) B) Compare your answers with the radius of the Sun and theEarth When a star like our Sun no longer has any hydrogen or heliumfuel for reactions in its core, it can colla[se and become a whitedwarf star. Often the star will blow off its outer layers and losesome mass before it collapses into a rapidly spinning, white dwarfstar. Suppose a star with mass 1Msun with radius 6.96 x108m and rotating once every 25 days becomes a whitedwarf with a mass of .6Msun and a rotation period of131s. A) What is the radius of the white dwarf (It isspherical) B) Compare your answers with the radius of the Sun and theEarth

Explanation / Answer

A)According to Kepler's third law we have (T2/r3) = constant or (T12/r13) =(T22/r23) or r2 = (T2/T1)2/3* r1 or r2 = (131/9 * 104) * 6.96 *108 = 101.3 * 104 m or r2 = (131/9 * 104) * 6.96 *108 = 101.3 * 104 m T2 = 131 s,T1 = 25 days = 25 * 60 * 60 s= 9 * 104 s r1 = 6.96 * 108 m B)the radius of the Sun rsun = 695500 km = 695500 *103 m = 69550 * 104 m the radius of the earth rearth = 6378.1 km =6378.1 * 103 m = 637.81 * 104 m

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