Dark Matter Facts
- Dark matter is space matter we cannot see because, unlike stars and galaxies, it does not give off light.
- There is much more dark matter in the Universe than bright. Some scientists think 90 percent of matter is dark.
- Astronomers know about dark matter because its gravity pulls on stars and galaxies, changing their orbits and the way they rotate (spin round).
- The visible stars in the Milky Way are only a thin central slice, embedded in a big bun-shaped ball of dark matter.
- Dark matter is of two kinds – the matter in galaxies (galactic), and the matter between them (intergalactic).
- Galactic dark matter may be much the same as ordinary matter. However, it burnt out (as black dwarf stars do) early in the life of the Universe.
- Intergalactic dark matter is made up of WIMPs (Weakly Interacting Massive Particles).
- Some WIMPs are called cold dark matter because they are travelling slowly away from the Big Bang.
- Some WIMPs are called hot dark matter because they are travelling very fast away from the Big Bang.
- The future of the Universe may depend on how much dark matter there is. If there is too much, its gravity will eventually stop the Universe’s expansion – and make it shrink again.
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