Abstract: Galaxies can be readily observed using the light from the billions of stars they contain. However, the stars are only part of what makes a galaxy. At the centre of almost all galaxies, we find a massive Black Hole (in fact they’re so large that astronomers call them supermassive) and we can observe very energetic outbursts caused by matter falling onto these black holes. These outbursts result in X-ray emission, and their observation requires dedicated satellite missions. While central supermassive black holes likely play a major role in determining a galaxy's stars, the black hole makes up only a very small fraction of a galaxy's mass. In massive galaxies and clusters of galaxies, most of the mass is made up of Dark Matter. This mysterious component does not interact with light - we cannot see it directly, only observe its gravitational influence. However, galaxies and clusters of galaxies are filled with very hot gas, which we can observe and use to trace the Dark Matter. Between galaxies there is an even more elusive component in the Universe - Dark Energy, which acts to suppress gravitational attraction. In this talk, I will show how we use X-ray and optical observations to trace how the Dark Matter is distributed and how clusters of galaxies evolve with the expansion of the Universe over time.
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