Commentary: Euclid's first public data release

“The fact that we’ve already found hundreds of gravitational lenses in this small section of Euclid’s observations confirms our predictions, that we will uncover many more – potentially hundreds of thousands. These lenses occur when massive objects, like galaxies and galaxy clusters, bend light from more distant sources, helping us map dark matter at an unprecedented detail. 

"We also expect to discover many thousands of Einstein rings – striking circles of light formed when background galaxies align perfectly with foreground lenses. But most exciting are the ultra-rare double-source plane rings, where not one but two galaxies are lensed by the same object. Until now, only four have been found; Euclid has already doubled that number, and we predict there could be up to a thousand more to be discovered over the five-year course of its mission.  

"Beyond mapping dark matter, gravitational lensing offers a powerful new tool for measuring dark energy in the universe, which is vital if we’re to understand why the expansion of the universe is accelerating.”