Space matter that can not be seen
- space matter that can not be seen is called dark matter – it does not give off light – Â unlike stars and galaxies.
- much more dark matter in the Universe than bright. (some scientists think 97% 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.
- visible stars in the Milky-Way galaxy are only thin part – embedded in a big ball of dark matter.
- dark matter is of two kinds; the matter in galaxies (galactic) and the matter between them (intergalactic).
- Galactic dark matter Â – Â similar to ordinary matter – however, it burnt out early in the life of the Universe.
- Intergalactic dark matter Â – Â made up of WIMPS (Weakly Interacting Massive Particles)
Weakly Interacting Massive Particles (WIMPs)
- some WIMPs are called “cold” because they are travelling slowly.
- other WIMPs are called “hot” because they are travelling very quickly.
Future of the Universe
- depends on how much dark matter there is – if there is too much, its gravity will eventually stop Universe’s expansion, and make it shrink again. (See The Big Bang)
- wikipedia: Â Dark Matter