Physics

In search of dark matter

Print edition : April 14, 2017

A picture released by the European Southern Observatory shows a representation of rotating disc galaxies of the early universe (right) and the present day (left). Such galaxies in the early universe were less influenced by dark matter (shown in red), as it was less concentrated, resulting in the outer parts of distant galaxies rotating more slowly than comparable regions in present-day galaxies. Photo: L. CALCADA/AFP

Figure 1. A pie chart indicating the proportional composition of different mass or energy components of the universe. Roughly 95 per cent is exotic dark matter and dark energy. The percentage fractions shown are based on pre-Planck Mission results. The post-Planck Mission (2015) values are as indicated in the article. Photo: WIKIPEDIA

Figure 2. Examples of particle dark matter interactions that can be detected. WIMP annihilation producing pairs of Standard Model particles (photons, neutrinos or electrons), which can be observed (left). A WIMP undergoing an elastic scatter with a nucleus, whose recoil energy can be detected (right). Photo: Adapted from Daniel A. Bauer FERMILAB-CONF-05-438-E

Figure 3. When a WIMP-a hypothetical dark matter particle-collides with a xenon atom, the xenon atom emits a flash of light (gold) and electrons. The flash of light is detected at the top and bottom of the liquid xenon chamber. An electric field pushes the electrons to the top of the chamber, where they generate a second flash of light (red). Photo: Matthew Kapust/ Sanford Underground Research Facility

Inside the LUX detector. Photo: SLAC National Accelerator Laboratory, Stanford, U.S.

About 85 per cent of the mass of the universe consists of dark matter. But particle physicists are still in the dark about what it is and what its properties are.
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