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Astronomers often detect stars that are rotating extremely rapidly,known as neut

ID: 1749933 • Letter: A

Question

Astronomers often detect stars that are rotating extremely rapidly,known as neutron stars. They are believed to have been formed fromthe collapse of a larger star under its own gravitationalattraction. Suppose a star is the same size as the Sun (radius6.96E8 m), but two times as heavy, and it rotates 1 revolutionevery 10 days. If it were to undergo gravitational collapse to aneutron star of radius 10 km, how many revolutions per second wouldit spin? Assume the star is a uniform sphere at all times.

Explanation / Answer

According to Kepler's third law (T^2/r^3) = (T1^2/r1^3) or T1^2 = (T^2/r^3) * r1^3 or T1 = (r1/r)^(3/2) * T r1 = 10 km = 10 * 10^3 m r = 6.96 * 10^8 m T = 1 rev/10 days = 1 * (1/10 * 24 * 60 * 60) rev/sec = 1.15 *10^-6 rev/s
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