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"When the astronauts go into space, what protects them from solar radiation (microwaves, etc.) which the ozone and atmosphere protect the Earth from?"
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Question
Why is space so dark?
Suppose that most of the universe is made of dark matter. Dark matter is a nonluminous mass whose presence can be inferred only because of its gravitational influence on luminous matter. Dark matter may constitute as much as 99% of all mass in the universe. Even though the composition of dark matter is not completely known, let's suppose that it is made of normal particles-protons, neutrons, and electrons. We already know that these particles are not assembled into stars that shone, or we would be able to see them. Neither can dark matter be in the form of dust and gas, or again, we could detect them. The protons and neutrons could be in the form of black holes, brown dwarfs, or white dwarfs. The latter two types of objects do emit some radiation but have such low luminosities that they cannot be seen at distances greater than a few thousand light years.
November 4, 2001
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