• Question: what is darkmatter and how does it work

    Asked by shadowfire to Aled, Ellie, Fiona, Kev, Willem on 10 Mar 2014.
    • Photo: Eleanor Parker

      Eleanor Parker answered on 10 Mar 2014:

      Hi shadowfire,
      Matter is what makes up the universe, everything we can see. Dark matter is matter that doesn’t absorb or give out light so we cannot see it. All matter causes forces on the things around it. Physicists and astronomers calculate dark matter (using lots of complicated maths) to be there by looking at the effects of gravity and other forces on the matter we can see. For example if there is a group of stars or planets circling what looks like an empty space, there is actually dark matter there as the gravity it has is causing the planet/stars to circle where they are but we cannot see it.

    • Photo: Willem Heijltjes

      Willem Heijltjes answered on 10 Mar 2014:

      Hi Shadowfire!

      Dark Matter comes from the following problem:

      On the one hand, we can estimate the mass of a galaxy by counting the number of stars, from the light they emit. On the other hand, we can estimate the mass of a galaxy by how fast it spins, and how much gravity there must be to make it spin that fast. However, when we do that, we don’t get the same estimate! There is more “gravity” than there is “light”!

      So, the idea is that there must be mass that we cannot see: dark matter… There are two ideas what this could be: MACHOs (MAssive Compact Halo Objects), planets like Jupiter but flying freely through space, instead of orbiting a star; or WIMPS (Weakly Interacting Massive Particles), sub-atomic particles like protons and electrons, that are very heavy but not electrically charged.

      But we don’t yet know what dark matter really is, or whether something else entirely is needed to explain the difference between the gravity and the light we see!

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