I have always heard about dark matter, but I do not know what it means, what its uses are, and does it really exist?
In: Chemistry
If you swing something at the end of a rope in a circle, you will feel that you need to pull to keep it from flying of. The faster you swing it, the harder you need to pull.
When looking at distant galaxies we can do the opposite, look at how fast the stars move to figure out how strongly they are held.
Unless we have completely misunderstod physics, they are held by the mass of the galaxy further inward. We have a decent understanding of stars, so we know how heavy the stars are, and they are not heavy to explain the motions we observe. One possible explanation is that there is more mass, that does not emit light: dark matter.
Exactly what this dark matter is is not known. Some of may be perfectly normal matter, but too cold to emit light.
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