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- Nov 27, 2023
- 4 min read

Euclid exploring the mysteries of the dark universe

Updated: Jan 7

First images of the dazzling edge of darkness from Euclid

Euclid is a mission that the European Space Agency (ESA) launched on July 1, 2023, to explore the composition and evolution of the dark Universe and reveal the role of gravity and the nature of dark energy and dark matter[1]. To demonstrate the impressive capabilities of this telescope, the Euclid team released the first images just three months after its launch.

Artist's impression of the Euclid spacecraft, a medium-class mission in ESA's Cosmic Vision program. The illustration depicts Euclid's mission to investigate the Universe's expansion over the past ten billion years, exploring cosmic epochs from pre-acceleration to the present. In the background, a composite image of the massive galaxy cluster MACS J0717.5+3745 is shown, combining X-ray data from NASA's Chandra X-ray Observatory (in blue and purple hues) with optical observations from the NASA/ESA Hubble Space Telescope

Euclid concept image

A photo of the structural and thermal model of the Euclid satellite during thermal qualification tests at Thales Alenia Space’s premises in Cannes, France. The satellite is integrated in near-flight configuration, including the payload and service modules, and is ready for mechanical vibration tests in the coming weeks. Euclid is a medium-class mission in ESA's Cosmic Vision programme designed to investigate the expansion of the Universe over the past ten billion years. The satellite model, though not the flight model, undergoes extreme thermal and mechanical stress testing to validate predictions and ensure its readiness for launch. The main design drivers include the quality and stability of the integrated optical system, efficient sky survey capability, accurate pointing, and reliable data transmission. Thales Alenia Space, the mission’s prime contractor, draws on experience from ESA’s Herschel and Planck missions in designing Euclid. The satellite's unique feature is its ability to maintain stable optical performance during extreme attitude changes, proven through recent thermal vacuum tests. Integration and testing of the Euclid telescope and service module have begun, with final tests scheduled for 2022 before the planned launch

Structural and Thermal model of Euclid

Credit: ESA/Euclid/Euclid Consortium/NASA

But what is Euclid? Euclid is a space telescope that will be operating at the Sun-Earth L2 Lagrangian point or about 4 times the distance between the Earth and the Moon. It has a 1.2 meter diameter main mirror and two detectors, one that will take images in visible light (called VIS) and another for spectra and photometry in infrared light (called NIPS). Euclid is a three-mirror Korsch configuration telescope with size 4.5 meters tall and 3.1 meters wide. Its field of view of the sky is 0.79 x 1.16 deg^2, or about 1.5 Moons x 2.3 Moons. Its planned lifetime is six years but could last 10 or 11 years[2]. It also has a great resolving power, and although it is less than the resolving power of the Hubble Space Telescope or the James Webb Space Telescope, its wider field of view makes it ideal for mapping the large-scale structure of the Universe across space and time. It will be able to observe billions of galaxies out to 10 billion light-years and across more than a third of the sky; it will make a 3D map of the Universe.

The 1.2-meter diameter main mirror of ESA’s Euclid mission, seen during assembly, integration, and testing. This mirror, along with five smaller mirrors, is made from silicon carbide (SiC), a ceramic naturally found in space. SiC, known for its hardness and lightness compared to glass, is a key material for space-based astronomy due to its high thermal conductivity and resistance to temperature shifts. The mirror's manufacturing involved shaping SiC powder into a solid block, sintering at 2100°C, coating with additional SiC, polishing, and silver coating. Euclid's instruments, including the VISible instrument (VIS) and the Near Infrared Spectrometer and Photometer (NISP), utilize these mirrors to map the 3D distribution of galaxies up to 10 billion light-years away, contributing to our understanding of dark energy and dark matter in the Universe.

Credit: ESA/Euclid/Euclid Consortium/NASA

During the first months after launch, the ESA team tested and prepared the observatory for science observations, what we call commissioning the telescope. Finally, ESA released the first full-color images of five objects close by and into the distant Universe on November 2, 2023,[3]. These images reveal the potential of this telescope and what it can do with its razor-sharp astronomical images across such a large patch of the sky.

Euclid, the dark Universe detective, captured one of its first images of the 'Hidden Galaxy' (IC 342 or Caldwell 5), showcasing its exceptional sensitivity and optics. The galaxy, challenging to observe due to its location behind the Milky Way's disc, is obscured by dust, gas, and stars. Euclid's near-infrared instrument allowed it to penetrate the dust, revealing the light from numerous cool and low-mass stars that constitute the galaxy's mass. This image represents Euclid's mission to unveil the hidden influence of dark matter and dark energy on billions of galaxies throughout its lifetime

Credit: ESA/Euclid/Euclid Consortium/NASA

One of these images is the spiral galaxy IC 342 or Caldwell 5. This galaxy is hard to observe because the dust, gas, and stars in the disk of our galaxy obscure our view. However, Euclid NISP can peer through the dust and measure the whole IC 342 galaxy in a single shot! This image reveals the light from many cool and low-mass stars that dominate the galaxy's mass[4]. However, there is more information that can be extracted from this image. A closer look at the region outside the galaxy shows many distant galaxies, which can be used to construct a 3D image of the Universe. This image was created with data taken over one hour of observations with the VIS and NISP detectors. The 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.

Euclid captures a panoramic and detailed view of the Horsehead Nebula, also known as Barnard 33, situated in the Orion constellation. The Horsehead, resembling a dark cloud shaped like a horse's head, is approximately 1375 light-years away, making it the nearest giant star-forming region to Earth. Positioned just south of the star Alnitak in Orion's three-star belt, it is part of the expansive Orion molecular cloud. Euclid's exceptional ability to quickly image vast sky areas in high detail is evident in this one-hour observation. The image showcases the mission's distinctive color palette, representing different wavelengths. Hot stars appear white-blue, excited hydrogen gas in blue, and regions rich in dust and molecular gas in a clear red hue. Distant redshifted background galaxies appear very red. The starfield, with stars of varying sizes and colors, adds to the cosmic tapestry of the image.

Horsehead Nebula View from Euclid

Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre (CEA Paris-Saclay), G. Anselmi

Another striking image is the panoramic view of the famous Horsehead Nebula in the constellation of Orion. At approximately 1,375 light-years away, the Horsehead is the closest giant star-forming region to Earth. Located in the belt region of the Orion Nebula, just to the south of star Alnitak, this region of star formation took its name from the shape of the most prominent feature in the region, which evokes the head of a horse. With Euclid, the team constructed a wide view of this region in about one hour. The wispy clouds in the top part of the image, which look like fog lifting from the cloud, are ionized hydrogen (hydrogen atoms that have lost their electrons). These are produced by the dissociation or splitting of molecules at the most exposed part of the dense cloud, due to the intense radiation produced by stars well beyond the top of this image.

A groundbreaking snapshot from Euclid showcasing 1000 galaxies within the Perseus Cluster and over 100,000 galaxies in the background, each hosting hundreds of billions of stars. Previously unseen faint galaxies, some as distant as 10 billion light-years, are revealed in unprecedented detail. This large-scale image aids cosmologists in mapping the distribution and shapes of galaxies, unraveling insights into how dark matter influenced the formation of the observable Universe. The Perseus Cluster, located 240 million light-years away, is among the most massive structures known, containing thousands of galaxies immersed in a vast cloud of hot gas. Astronomers have demonstrated that galaxy clusters like Perseus could only have formed if dark matter is present in the Universe.

Perseus Cluster Credit: ESA/Euclid/Euclid Consortium/NASA

The image of the Perseus Cluster, at about 240 million light-years away, is also spectacular. It shows, with great detail, the approximately 1000 galaxies members of the cluster and about 100,000 distant galaxies scattered all around the image, capturing light that might have taken about 10 billion years to reach us. Studying this cluster could provide clues to understanding dark matter, as the total mass of all the galaxies in the Perseus cluster is not enough to explain the measured velocities of each of them.

A square astronomical image showcasing hundreds of thousands of stars scattered across the black expanse of space. The stars exhibit variations in size and color, ranging from blue (indicative of younger stars) to white and yellow/red (characteristic of older stars). Concentrated at the center of the image, more stars form a spheroid conglomeration known as a globular cluster, held together by gravity. Some stars appear slightly larger, featuring six diffraction spikes."

NGC6397 Credit: ESA/Euclid/Euclid Consortium/NASA

Euclid also observed a wide area of the globular cluster NGC 6387. These types of clusters have hundreds of thousands of stars held together by gravity, similar to what holds together the galaxies in the Perseus Cluster but on a much smaller scale. This cluster is just 7,800 light-years from Earth and is the second closest globular cluster to us.

A square astronomical image featuring a black expanse of space speckled with numerous stars. Most stars appear as pinpoints, while more concentrated stars form an irregular round shape at the center of the image, indicative of an irregular galaxy. The central region of the galaxy appears whiter, while the edges exhibit a yellowish hue. Throughout the galaxy, several pink bubbles signify active star-forming regions. Stars vary in color, ranging from blue to white and yellow/red against the cosmic backdrop. A few stars are slightly larger, characterized by six diffraction spikes

NGC6822 Irr Galaxy Credit ESA/Euclid/Euclid Consortium/NASA

Finally, we have an impressive high-resolution image of the irregular galaxy NGC 6822 that Euclid was able to construct in about one hour. This galaxy, located 1.67 million light years from Earth, might have relevant information to the study of galaxy formation, which tells us that smaller irregular galaxies like NGC 6822 help to form larger and more well-designed galaxies, like our own.

With Euclid, astronomers will explore how the Universe has expanded and how structure has formed over cosmic history, revealing more about the role of gravity and the nature of dark energy and dark matter.

References:

[1] https://www.esa.int/Science_Exploration/Space_Science/Euclid_overview

[2] https://www.esa.int/ESA_Multimedia/Images/2023/06/Eye_of_Euclid

[3]https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_s_first_images_the_dazzling_edge_of_darkness

[4]https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_s_view_of_spiral_galaxy_IC_342

Euclid exploring the mysteries of the dark universe

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