• Question: @Claire, what is dark matter

    Asked by 563thuc23 to Claire, Liad, Ruth, Ryan, Mako on 23 Jun 2015.
    • Photo: Claire Bryer

      Claire Bryer answered on 23 Jun 2015:

      I really don’t know much about this as I’m not a Physicist, so maybe @Ryan can help you a bit, as I’ll be pretty rubbish!

      But from what I understand, dark matter is matter that cannot be seen through a telescope, but accounts for most of the matter in the Universe. It cannot be detected by light or radiation.

    • Photo: Ryan Cheale

      Ryan Cheale answered on 23 Jun 2015:

      The Wilkinson Microwave Anisotropy Probe (WMAP) satellite ran for a 9 year mission and undertook data analysis of the cosmic microwave background (CMB) temperature fluctuations to determine the basic parameters which make up the universe. WMAP found that, of its total mass, the universe is made up of 4.6% baryonic matter, 71.6% dark energy and 24% dark matter.

      Dark matter is a conjecture of what accounts for the total mass in the universe. This has been proposed both by theory, and observational data. A discrepancy in measured and calculated velocities was shown in both 1930 by Fritz Zwicky , and in 1970 by Vera C.Rubin

      There are two conclusions which can be drawn from the above observations. Namely, Modified Newtonian Dynamics (MoND) and that the galaxies contain another material which extends away from the visible range of the galaxy.
      For the second conclusion there are several dark matter candidates;

      • Massive Compact Halo Objects (MaCHOs)
      • Axions
      • Weakly Interacting Massive Particles (WIMPs) (the main one)

      WIMP candidates are primarily based off of the supersymmetric partner of the neutrino, the neutralino, which is a viable candidate for the WIMP. WIMPs interact via the weak force and also have gravitational interaction. For this reason, WIMPs are difficult to detect as they produce no electromagnetic waves.
      Their mass scale is around the 70 GeV range; this plays a key role in direct detection searches as, for nuclear recoil, maximization occurs when a particle interacts with another particle of a similar mass. For example, NaI is used, as the atomic mass of the NaI particles is on a similar scale to that of the predicted WIMP mass.
      WIMPs are gravitationally drawn to the centres of high mass stellar objects, such as the Sun or Earth. WIMPs gravitationally attracted towards and through the sun are often gravitationally bound when they lose energy through the scattering of nuclei. Trapped WIMPs either annihilate or escape via evaporation

      Big answer, sorry!! Your question is very good and it’s a very interesting topic 🙂

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