English: This incredible snapshot from the Euclid space telescope is a revolution for astronomy. The image shows 1,000 galaxies belonging to the Perseus Cluster, and more than 100,000 additional galaxies further away in the background, each containing up to hundreds of billions of stars.
Many of these faint galaxies were previously unseen. Some of them are so distant that their light has taken 10 billion years to reach us. By mapping the distribution and shapes of these galaxies, cosmologists will be able to find out more about how dark matter shaped the Universe that we see today.
This is the first time that such a large image has allowed us to capture so many Perseus galaxies in such a high level of detail. Perseus is one of the most massive structures known in the Universe, located ‘just’ 240 million light-years away from Earth, containing thousands of galaxies, immersed in a vast cloud of hot gas. Astronomers demonstrated that galaxy clusters like Perseus can only have formed if dark matter is present in the Universe.
Read more about Euclid’s view of the Perseus cluster of galaxies
Explore this image at the highest resolution in ESASky
Read more about Euclid's first images
[Technical details: The data in this image were taken in just five hours of observation. This colour image was obtained by combining VIS data and NISP photometry in Y and H bands; its size is 8,800 x 8,800 pixels. VIS and NISP enable observing astronomical sources in four different wavelength ranges. Aesthetics choices led to the selection of three out of these four bands to be cast onto the traditional Red-Green-Blue colour channels used to represent images on our digital screens (RGB). The blue, green, red channels capture the Universe seen by Euclid around the wavelength 0.7, 1.1, and 1.7 microns respectively. This gives Euclid a distinctive colour palette: hot stars have a white-blue hue, excited hydrogen gas appears in the blue channel, and regions rich in dust and molecular gas have a clear red hue. Distant redshifted background galaxies appear very red. In the image, the stars have six prominent spikes due to how light interacts with the optical system of the telescope in the process of diffraction. Another signature of Euclid special optics is the presence of a few, very faint and small round regions of a fuzzy blue colour. These are normal artefacts of complex optical systems, so-called ‘optical ghost’; easily identifiable during data analysis, they do not cause any problem for the science goals. ]
[Image description: This square astronomical image shows thousands of galaxies across the black expanse of space. The closest thousand or so galaxies belong to the Perseus Cluster. The most prominent members of the cluster are visible in the centre of the image and appear as large galaxies with haloes around them in yellow/white, comparable to streetlamps in a foggy night. The background of this image is scattered with a hundred thousand more distant galaxies of different shapes, ranging in colour from white to yellow to red. Most galaxies are so far away they appear as single points of light. The more distant a galaxy is, the redder it appears.]