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Question
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 1/1000 that of the Sun, and that dark matter has a mass 10 times that of the luminous Milky Way galaxy with its $10^{11}$ stars of average mass 1.5 times the Sun’s mass.
$1.5\times 10^{15}\textrm{ MACHO'S}$
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