Euclid offers best-ever 3D map of the universe to date

The Euclid Consortium and the European Space Agency (ESA) have released the first major batch of data from the Euclid space telescope. This release, which captures light from more than a billion objects and covers an area of sky equivalent to 9,500 full moons, lays the foundation for Europe’s dark universe detective’s largest-ever 3D map of the cosmos. Several German research facilities play crucial roles in the Euclid mission’s success.

The new data release, named DR1 Foundation, comprises some 13 months of observations and marks the first major release of mission data since the space telescope’s launch in mid-2023. For the first time, it provides scientists with the puzzle pieces needed to begin constructing a detailed 3D map of the cosmos—crucial for solving the many mysteries of the dark universe (including dark energy, dark matter and the cosmic web of galaxies and galaxy clusters).

Spectra and images, including large sky mosaics, accompany the data. “These are far more than beautiful pictures; today marks a scientific milestone in our study of the cosmos,” says ESA’s director of science, Carole Mundell. This unprecedented collection of optical and near-infrared observations represents the largest map of the sky of its kind ever produced from space.

Brand-new science and discovery

Today’s release is the first to demonstrate Euclid’s capabilities as a sky surveyor. Its breadth, panoramic mosaics and wide sky coverage in visible and near-infrared light support a wide range of new science. Analysis of about 10,000 science images from the DR1 Foundation reveals unprecedented numbers of cosmic objects, including:

• More than 900 million galaxies
• Around 15,000 strong gravitational lensing candidates
• More than 60 million quasar candidates, the brilliant cores of distant galaxies
• Spectra from more than 160 million sources
• Euclid Wide Survey results from 1,900 deg² of sky—around 14% of the sky area planned for the six-year mission
• 1.7 million GB of data

“This is a change in scale from Euclid’s previous releases, which included a few days of observations over around 60 deg² of sky,” says Valeria Pettorino, Euclid project scientist at ESA. “We’re now releasing more than a year of data covering a significantly larger area. This unlocks groundbreaking science.”

Critical optical components

The images were obtained with Euclid’s VIS (the 600-megapixel camera for visible light) and NISP (Near-Infrared Spectrometer and Photometer) instruments, for which the Max Planck Institute for Astronomy (MPIA) in Heidelberg and the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching near Munich contributed critical optical components. The data are being processed into scientifically usable data at various locations, including the German Science Data Center (SDC-DE), operated by MPE.

Scientists at more than 300 research institutions in Germany and abroad, including Max Planck Institutes and Ludwig Maximilian University (LMU) in Munich, analyze them, and over 2,500 researchers use the data.

“This is also possible because the optics built here in Munich using the most innovative methods allow images of outstanding quality to be transmitted to the ground station. More than 15 years of preparatory work prior to launch, and over three years in orbit, are now rewarding us with results that are groundbreaking,” says Frank Grupp (LMU/MPE), German Euclid project manager and optical architect of the mission.

However, those data have to be corrected for instrumental effects and translated into physical quantities. MPIA scientists, mainly Mischa Schirmer and Kerry Paterson, coordinate and organize this process, known as calibration. “This task ranges from designing and planning the required calibration observations to characterizing the properties of the telescope and its instruments and analyzing whether these properties change over time,” says Schirmer.

“I am delighted and excited that we can now take another step toward understanding why the expansion of the universe is accelerating—a mystery that has challenged physics for nearly 30 years,” says Jochen Weller (LMU). “After so many years of preparation, it is a real joy to see the data becoming available and this next stage of our journey beginning.”

Euclid’s first major milestone

Overall, the DR1 Foundation release marks the first major milestone of the Euclid mission, many years after its conception. From Germany, Ralf Bender (LMU/MPE), Hans-Walter Rix (MPIA) and Peter Schneider (University of Bonn) are founding members of the Euclid project and were instrumental in its inception. Without them, the mission would not be where it is today. Bender and Rix also represent Germany on the Euclid Consortium Board, while Schneider chairs the Editorial Board and plays a key role in organizing the peer review of all publications across the Euclid Consortium.

Already with this data release, Euclid provides the largest space-based image data set available to astronomy to date and for the foreseeable future. Processing these vast amounts of data poses immense challenges for the participating computing centers, further aggravated by the current tight availability of new hardware. Added to this are the exceptionally high requirements for photometric precision—that is, the accuracy with which the brightness of astronomical objects is determined.

“It is all the more exciting to see how the data processing pipelines developed by our team over the years are now coming together and delivering scientific results,” says Maximilian Fabricius (LMU/MPE), head of the German Euclid Data Center. Astronomers use the term ‘pipelines’ to describe the scientific software that produces progressively refined results step by step from raw data. These pipelines are based on software and algorithms prepared at LMU and now run across computing centers throughout Europe and in the U.S.

A machine for discovering rare objects

In space, above Earth’s image-blurring and light-dimming atmosphere, Euclid can complete deep and wide surveys of the sky in a way that ground-based telescopes cannot. As a result, this data release delivers vastly more cosmic objects than any preceding survey, pushing the boundaries of detection for rare and distant objects. These include strong gravitational lenses and galaxy clusters.

The strong gravitational lenses sought by Euclid are extremely rare and form when the light traveling to us from distant galaxies is significantly distorted by a foreground galaxy. This release contains the largest catalog of strong lenses ever—larger than all previous catalogs combined. These phenomena allow scientists to “weigh” individual galaxies, including their invisible dark matter, and to explore how the universe is expanding.

Galaxy clusters reveal how matter clumps together and how cosmic structure grows across the universe. “Euclid doesn’t just look far back in time—it does so across vast areas of the sky,” adds Barbara Sartoris of the JL Lagrange laboratory in Nice, France, who previously worked on Euclid data at LMU and MPE. “This gives us an unprecedented view of large samples of ancient galaxy clusters that were previously out of reach. We will explore these in the coming months to learn how these giants grew and to decipher what they reveal about the dark universe.”

Additional ground-based data on fields covered in the DR1 release, whose preparation was led by scientists at LMU, help interpret Euclid’s observations in the context of cosmology and cosmic structure research.

Just the beginning

With this release, Euclid begins to reveal the dark cosmos. Scientists can mine the data set to determine distances to individual galaxies and place them within the universe’s 3D structure, linking them to the vast, invisible mesh of the cosmic web. These distance measurements and mappings are achieved by Euclid through spectroscopy—by splitting the light from galaxies into ‘rainbows’ that reveal their distance (and, for especially bright ones, their origin and composition too).

“Euclid’s data have the potential to write an entirely new chapter in observational astronomy,” says Martin Kümmel (LMU). “Our images in the optical and the near-infrared, combined with the photometric redshifts, will lay the foundation for a vast number of exciting results.”

While enormous, the data set covers only about 14% of the total sky area that Euclid will survey. The full Data Release 1, due in mid-2027, will build on today’s release and add more crucial pieces to the cosmic puzzle, including observations of weak lensing to complement the strong lensing, and calculations of how galaxies and galaxy clusters fit into the cosmic web.

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Lisa Lock

BA art history, MA material culture. Former museum editor, paramedic, and transplant coordinator. Editing for Science X since 2021.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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