The Euclid Space Telescope reveals new insights into dark matter and dark energy

Euclid – named after the ancient Greek mathematician – is part of the European Space Agency (ESA) Cosmic Vision programme, with NASA providing some assistance in the form of instrumentation and scientific analysis. Launched in 2020 and placed at Sun-Earth Lagrange point L2, its mission duration is six years, during which time it studies the nature of dark matter and dark energy.*
Matter as we know it – the atoms in the human body, for example – is only a fraction of the total matter in the known universe. The rest, about 85 percent, is dark matter consisting of particles of an unknown type. This was first postulated in 1932, but has remained undetected directly. It is called dark matter because it does not interact with light. Dark matter interacts with ordinary matter through gravity, binding galaxies together like an invisible glue.
While dark matter pulls matter together, dark energy is pushing the universe apart, at an ever-increasing speed. In terms of the complete mass-energy content of the universe, dark energy dominates. Even less is known about dark energy than dark matter, having only been discovered by astronomers in 1998 (the Nobel Prize for Physics was subsequently awarded for their work in 2011).
Using a 1.2m (3' 11") wide-view telescope at visible and near-infrared wavelengths, Euclid maps the shape, brightness and 3D distribution of 2 billion galaxies covering over one-third of the sky. It measures the geometry and growth rate of the universe in higher resolution than was ever possible before, through a combination of weak gravitational lensing, redshift-space distortions and galaxy cluster observations.
Taken together, these ultra-precise measurements offer the best explanation yet of how the acceleration of the universe has changed over time – revealing new clues about the origin, evolution and ultimate fate of the cosmos – and the role of dark matter and dark energy in each of these processes, revolutionising our understanding of these hitherto largely unknown phenomena.

Credit: ESA