Chapter 34: Q16CQ (page 1237)
Is the event horizon of a black hole the actual physical surface of the object?
It isn't, however it is necessary for comprehending how black holes function.
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If the dark matter in the Milky Way were composed entirely of MACHOs (evidence shows it is not), approximately how many would there have to be? Assume the average mass of a MACHO is\({\rm{1/1000}}\)that of the Sun, and that dark matter has a mass\({\rm{10}}\)times that of the luminous Milky Way galaxy with its\({\rm{1}}{{\rm{0}}^{{\rm{11}}}}\)stars of average mass\({\rm{1}}{\rm{.5}}\)times the Sun’s mass.
Find the approximate mass of the luminous matter in the Milky Way galaxy, given it has approximately\({\rm{1}}{{\rm{0}}^{{\rm{11}}}}\)stars of average mass\({\rm{1}}{\rm{.5}}\)times that of our Sun.
Suppose black holes radiate their mass away and the lifetime of a black hole created by a supernova is about \({\rm{1}}{{\rm{0}}^{{\rm{67}}}}\)years. How does this lifetime compare with the accepted age of the universe? Is it surprising that we do not observe the predicted characteristic radiation?
Another known cause of red shift in light is the source being in a high gravitational field. Discuss how this can be eliminated as the source of galactic red shifts, given that the shifts are proportional to distance and not to the size of the galaxy.
(a) A particle and its antiparticle are at rest relative to an observer and annihilate (completely destroying both masses), creating two\({\rm{\gamma }}\)rays of equal energy. What is the characteristic\({\rm{\gamma }}\)-ray energy you would look for if searching for evidence of proton-antiproton annihilation? (The fact that such radiation is rarely observed is evidence that there is very little antimatter in the universe.) (b) How does this compare with the\({\rm{0}}{\rm{.511 MeV}}\)energy associated with electron-positron annihilation?
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