‘Gravitational lensing: Studying dark matter and dark energy with light rays’

Almost everything we know about the universe comes from the observation of light. However, 95% of the matter and energy in the universe is “dark”, of a form that does not emit electromagnetic radiation. This matter surrounds galaxies in dark halos, whose mass is ten times greater than that of the stars and gas that we see in them, and its clustering drives the formation of galaxies, stars and planets. Dark energy drives an accelerating expansion of the universe, counter to the expected deceleration that ordinary gravity would cause. One of the best ways to study dark matter and energy is to study how light rays are bent in gravitational fields; a technique known as gravitational lensing. This talk describes its use in mapping the distribution of dark matter in galaxies and the universe. Investigating dark energy is the primary mission of the Euclid satellite ESA (to be launched in 2019) and large ground-based telescope projects such as KiDs (the Kilo-Degree Survey) of the European Southern Observatory.