Galaxy clusters are the most massive observable structures in the Universe; most of their mass is believed to be made of dark matter. Dark matter has remained `directly’ invisible to us so far, however one way to observe it `indirectly’ is through gravitational lensing, the bending of light rays from background galaxies as they travel through, and in the vicinity of galaxy clusters.

We propose, through an international collaboration, to combine the best observations ever obtained of massive galaxy clusters from space with state-of-the art methods based on X-ray and lensing analyses, to constrain their physics, map their dark matter content and constrain its particle nature. Until the nature of dark matter gets identified, this combined analysis remains one of the most promising avenues to constrain its spatial distribution and potentially constrain its nature, such as self-interacting dark matter particles.

The team we are putting together includes more than 10 researchers from France, UK, USA, China, Japan, Israel and Switzerland, and world experts in the areas of lensing and X-ray analyses of galaxy clusters.

Adding to that, building a complete picture of those massive clusters and using their gravitational lensing power as cosmic telescopes will allow us to probe the high-redshift Universe, learn about early galactic assembly and clustering, and prepare targets for follow-up with the upcoming James Webb Space Telescope (JWST).