What is the difference between dark matter and dark energy?
In summary, dark matter attracts, dark energy repels.
In detail, scientists don't know a lot about dark matter and dark energy, except that they make up more than 90 percent of all the matter and energy in the universe; in other words, they know very little about almost everything.
Dark matter produces no detectable energy, but astronomers know it exists because it exerts a gravitational pull on the visible matter around it, like stars and galaxies. The Milky Way galaxy appears to have a "halo" of dark matter that spans hundreds of thousands of light-years and far outweighs all the visible stars, planets, and gas clouds. Some of the dark matter of the universe may consist of black holes, brown dwarfs, large planets, and other "normal" objects that are just too faint to detect. On the other hand, some or all of the dark matter may consist of some unknown type of subatomic particles.
Dark energy appears to cause the universe to expand faster, driving galaxies away from each other at an ever-increasing pace. It may take the form of a "vacuum energy" that pops into existence on the smallest scales of space. Observations by instruments on balloons and orbiting spacecraft confirm that almost two-thirds of all matter and energy in the universe comprises this mysterious dark energy.
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