File:What Euclid will measure- baryonic acoustic oscillations ESA24866727.png

English: To understand more about the dark Universe, ESA’s Euclid will measure a phenomenon known as ‘baryonic acoustic oscillations’ that affect the distribution of galaxies on a very large scale.
When the early Universe first expanded, the formation of protons and neutrons created sound waves (bubbles) that rippled through the hot particle-radiation soup. About 300 000 years after the Big Bang, when the Universe had cooled down enough for atoms to form and light to travel freely, these waves froze in place. Over time, slightly more galaxies formed in clusters along the frozen ripples. The ripples stretched as the Universe expanded, increasing the distance between galaxies. Scientists refer to these ripples in the large-scale distribution of galaxies as baryonic acoustic oscillations.
ESA’s Euclid will study the distribution of galaxies over immense distances, teasing out these ripple patterns and determining their size. This enables us to measure accurately the rate of accelerated expansion of the Universe over time and teach us about the nature of dark energy and dark matter.
Euclid is a European mission, built and operated by ESA, with contributions from NASA. The Euclid Consortium is responsible for providing the scientific instruments and scientific data analysis. ESA selected Thales Alenia Space as prime contractor for the construction of the satellite and its service module, with Airbus Defence and Space chosen to develop the payload module, including the telescope. NASA provided the detectors of the Near-Infrared Spectrometer and Photometer, NISP. Euclid is a medium-class mission in ESA’s Cosmic Vision Programme.