In Simple Terms
The Euclid space telescope has collected an enormous set of pictures and measurements of galaxies. Scientists can use them to map where galaxies are, study how they gather together, and see how gravity bends light from distant objects. The data may help explain what the universe is made of, but turning it into answers will take years of research.
A Sky Survey That Goes Beyond Pretty Pictures
The European Space Agency’s Euclid space telescope has released a vast new collection of data, shifting its mission from photographing limited patches of sky to surveying a much broader stretch of the universe. The value of the release lies in more than the number of images: researchers can compare huge numbers of galaxies, chart how they cluster, and look for signs that gravity has distorted light from distant objects. Those comparisons may reveal a more detailed picture of how matter is distributed across the universe and how that distribution has changed over time.
Euclid was launched in July 2023 and carries a visible-light camera with a resolution of about 600 megapixels. Using this instrument, the telescope has recorded nearly a billion celestial objects, including more than 900 million galaxies and around 60 million objects that may be quasars. Quasars are extremely bright galactic cores. Their light is associated with intensely hot gas falling toward a supermassive black hole at the center of a galaxy.
These figures describe a huge haul of observations, but they do not mean that every object has been studied in detail or that its nature is settled. Objects identified as possible quasars still need to be examined and confirmed. And spotting a galaxy in an image does not, by itself, reveal its history or its exact place in the universe’s large-scale structure. The survey’s scientific value emerges when researchers analyze measurements together, comparing galaxies’ shapes and brightness and how they are distributed across enormous areas of sky.
The data collected so far amount to more than 1.7 million gigabytes. Carol Mundell, the European Space Agency’s Director of Science, described the release as a space survey on a remarkable scale, opening up new possibilities for astronomical exploration. In practical terms, the volume gives scientists a rich body of material to analyze, rather than just a handpicked set of striking images. A wider survey also makes it possible to study larger samples of objects and compare different regions of the sky within a single framework.
When Gravity Becomes a Cosmic Lens
One phenomenon that makes Euclid’s data especially useful is gravitational lensing. When light from a distant galaxy passes near a massive object on its way to us, that object’s gravity affects the light’s path and bends it. If the foreground object, the background galaxy, and the observer line up in just the right way, the light can appear brighter, or the galaxy’s image can look stretched or distorted. This natural lens can bring into view an object that would otherwise be fainter or harder to detect.
The required alignment does not happen everywhere, so strong gravitational lenses remain rare, even in a wide survey. Even so, Euclid has identified around 15,000 candidate strong lenses. The word “candidate” matters: these are cases that merit further examination, not objects that have all been definitively confirmed. This large collection gives astronomers a starting point for selecting promising examples and investigating them in detail.
Lensing does more than improve our view of distant objects. The distortion in the light from a background galaxy carries information about the gravity the light passed through—and therefore about the distribution of mass in the structure between us and that galaxy. Researchers can use these effects to study dark matter, which cannot be seen directly in the usual way but is inferred from its gravitational influence. In this way, lensing images help scientists read evidence that is not visible in the light itself.
Scott Gaudi, an astronomer at The Ohio State University, says the abundance of candidates made possible by Euclid is astonishing. He is not involved in the telescope’s program, but explains that studying lensing distortions allows researchers to estimate the mass associated with foreground structures, including dark matter. High-resolution observations are also essential for seeing these changes clearly: fine details in the background galaxy’s image help astronomers distinguish the effect of gravity from the galaxy’s original shape.
Euclid and Roman: Two Missions, Complementary Views
Euclid will not be the only telescope to make use of gravitational lenses. The Nancy Grace Roman Space Telescope, which observes in infrared, will also search for distant cosmic objects using this phenomenon. Euclid, by contrast, focuses on visible light and is designed to cover a broad area of the sky. Because the missions observe different parts of the spectrum and take different approaches to surveying the sky, they complement one another rather than simply repeating the same work.
According to Gaudi, Euclid is focused on expanding the area covered, while Roman will repeatedly image the same region at different rotation angles and through multiple filters. This contrast makes it possible to combine the broad sample provided by Euclid with more controlled, detailed observations of selected regions by Roman. When astronomers test large-scale results against detailed data from another mission, they can assess how robust their conclusions are instead of relying on just one kind of observation.
This comparison matters for research into dark matter and dark energy, two central topics in understanding the universe. But the data described here do not provide final answers to either question; they offer tools and samples that can help test ideas about both. Studying bent light, the distribution of galaxies, and the differences between what appears in visible and infrared light may add new evidence and constraints to researchers’ work.
From Galaxy Clusters to a Three-Dimensional Map
The new release also contains a wealth of information about galaxy clusters: groups of galaxies gathered together within vast cosmic structures. Comparing the locations of these galaxies and how they cluster helps scientists trace the way matter is organized in the universe. Studying clusters can test ideas about how the earliest structures formed and grew after the Big Bang—not just by examining individual galaxies, but by observing the relationships among large numbers of them.
Euclid aims to help astronomers determine where galaxies lie in relation to one another. If this work is carried out on a large scale, it could lead to a remarkably comprehensive three-dimensional map of the universe. Such a map would be more than a flat picture of the sky: including distances and spatial relationships would also show how galaxies are distributed in depth. The data could therefore connect the view of the sky from Earth with the structures that celestial objects form across space.
The survey’s breadth matters because ancient and rare clusters are not necessarily found in a small patch of sky. Barbara Sartoris, an astrophysicist at the Joseph-Louis Lagrange Laboratory in France, notes that looking far back in time while covering large areas makes it possible to assemble samples of ancient galaxy clusters on a scale that was not previously available. Studying these clusters in the coming months will help researchers investigate how the groups grew and what they may reveal about the universe’s invisible components.
Calling the clusters ancient does not mean the telescope is seeing the past only in a figurative sense. Light takes time to travel across cosmic distances, so images of faraway objects show them as they were at an earlier stage in their history. By surveying wide areas as well as distant objects, Euclid can give researchers large samples of these snapshots to compare. The mission thus brings together two important dimensions: looking back to earlier cosmic times and examining broad regions rather than focusing on only a handful of targets.
What Makes This Data Release a Turning Point?
The important step is not that Euclid has uncovered every secret of the universe on its own. Rather, it has provided a large observational foundation on which many lines of research can build. Researchers can study the shapes and clustering of galaxies, select promising lens candidates for closer analysis, and trace the growth of galaxy clusters. Each of these efforts requires its own investigation, but bringing them together in one survey helps place different phenomena in a broader context.
The sheer volume of measurements also presents a methodological challenge: candidate objects must be sorted, image quality assessed, and interpretations checked before they can be treated as established results. The need for caution is clear in the roughly 15,000 lens candidates and the nearly 60 million possible quasars. These enormous numbers open up new research opportunities, but they do not replace scientific work. Classification, analysis, and comparison are essential steps in turning observations into knowledge.
For that reason, the data release is best seen as the beginning of a new phase of questions, not the end of a completed discovery story. Researchers will study the information on galaxies, clusters, and gravitational lenses over the coming months and years, potentially improving our understanding of how matter is distributed and how cosmic structures evolve. The cooperation between Euclid and Roman gives astronomers two different ways to investigate interconnected topics, while preserving the distinct aims and methods of each mission.
The Bottom Line
Since its launch in July 2023, Euclid has delivered an enormous trove of observations captured with a visible-light camera of about 600 megapixels. Its haul includes nearly a billion objects—more than 900 million galaxies and around 60 million possible quasars—within a dataset exceeding 1.7 million gigabytes. Among its most striking results are around 15,000 candidates for strong gravitational lenses, along with a wealth of material for studying galaxy clusters.
The value of this collection lies in what it may reveal next: how galaxies gather, how clusters grow, and what the bending of light can tell us about unseen mass. Euclid’s visible-light survey and Roman’s infrared observations, including repeated imaging of selected regions, give astronomers complementary ways to investigate these questions. The release marks a major step toward a three-dimensional map of the universe, but it also begins a long effort to turn an immense volume of observations into a clearer understanding of the cosmos.