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A black hole has a Schwarzschild radius of 25 km. How much mass is contained in the black hole?

How large is the Schwarzschild radius of a black hole containing a mass equal to that of the Earth?

The visible light from a gamma ray burst has an apparent magnitude of 8.0. The distance of the galaxy in which the burst occurred is 3 billion pc. Find the absolute magnitude of the visible light. How does this compare with the absolute magnitude of the Sun? (Use Equation 16.3.)

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