An analysis of almost 15 million distant galaxies reveals that dark matter may be slightly less dense and more evenly distributed throughout space than was thought.
Dark matter makes up one-quarter of the Universe's mass, but is invisible and its presence can only be inferred from its gravitational effects. A team led by Hendrik Hildebrandt of the Argelander Institute for Astronomy in Bonn, Germany, and Massimo Viola of Leiden University in the Netherlands examined galaxy images taken by the European Southern Observatory's VLT Survey Telescope in Chile as part of the Kilo-Degree Survey. The researchers measured cosmic shear: the distortion of the shapes of background galaxies due to light that is warped by the gravitational effects of large-scale structures such as galaxy clusters. The team statistically measured how dark matter subtly distorted the galaxy images, and inferred its density from this.
If future measurements confirm this more-even distribution of dark matter, astrophysicists might need to revise their models of how the Universe evolved.
Mon. Not. R. Astron. Soc. (in the press); preprint at https://arxiv.org/abs/1606.05338 (2016)