Dark Matter

Space matter that can not be seen

Dark Matter

  • space matter that can not be seen is called dark matter – it does not give off light –  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.

Spin round

  • 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  –  similar to ordinary matter – however, it burnt out early in the life of the Universe.
  • Intergalactic dark matter  –  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)

More information


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