Dark Matter

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Two people have been credited for determining the need for dark matter. The first was astronomer Jan Oort, who back in 1932 measured the perpendicular motions of nearby stars relative to the disk of our galaxy. By studying the gravitational influence of the disk on these stars he was able to calculate the mass of the disk. The value he determined was twice as much as that inferred by the visible stars and nebulae in that …

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…and an observer on Earth. The MACHO focuses the light rays due to the MACHOs high gravitational field causing the light source to appear brighter to the observer. This effect was actually proven by Einstein in 1919. Whatever dark matter turns out to be, we know for certain that the universe contains large amounts of it. For every gram of glowing material we can detect, there may be tens of grams of dark matter out there.