30. A stellar black hole may form when a massive star dies. The star collapses d

Question

30. A stellar black hole may form when a massive star dies. The star collapses down to a single point. Our Sun will not become a black hole because it does not have enough mass, so let us imagine a black hole with eight times the mass of the Sun. A single point has no radius, but a black hole has an effective radius known as the Schwarzscfhild radius. If an object gets inside the Schwarzscfhild radius, it never escapes. The Schwarzscfhild radius of an eight solar-mass black hole is about 24 km. a. N Find the escape speed using the Schwarzscfhild radius. b. C Compare your answer to the speed of light and speculate on how these objects got the name ^''black hole.^''

Explanation / Answer

escape velocity of any object is given as sqrt(2*G*M/R)

where G=universal gravitational constant=6.673*10^(-11)
M=mass of the object=8*mass of the sun=8*1.989*10^30=1.5912*10^31 kg

R=radius of the object=24000 m

so putting all the values, we get

escape velocity=2.974*10^8 m/s

b) the speed of light is 3*10^8 m/s

so as the escape velocity is almost equal to speed of light, no object

, not even light can escape such massively dense objects

hence they are called black holes as they dont raidate anything and absorb everything.

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