Euclid opens a new search for gravitational lenses: citizens can help discover galaxies that bend space-time
ESA’s Euclid space telescope has once again opened the doors to the public for one of the most complex and exciting jobs in modern astronomy: the search for strong gravitational lenses, rare cosmic phenomena in which the enormous mass of a galaxy or galaxy cluster curves space-time and changes the path of light from a more distant background galaxy. This very phenomenon, often described as natural cosmic magnifying glasses, is today one of the important tools for understanding dark matter, dark energy, and the expansion of the Universe. The new Space Warps – ESA Euclid project invites citizens to help identify these rare systems based on fresh images from the mission, and scientists estimate that the new dataset could contain more than 10,000 previously unknown strong lenses.
Gravitational lensing is not science fiction, nor merely a visually impressive astronomical curiosity. It is a direct consequence of Einstein’s general theory of relativity, according to which mass curves space-time. When a massive galaxy lies between Earth and an even more distant source of light, its gravity can bend light rays so that observers see distorted arcs, multiple images of the same object, or an almost complete ring of light known as an Einstein ring. At the beginning of 2025, Euclid further attracted public attention precisely through the discovery of a striking Einstein ring around the galaxy NGC 6505, showing the sensitivity and resolution it possesses for detecting such phenomena.
From the first 500 candidates to a far larger new search
The value of the new campaign is best seen in light of the results Euclid has already delivered. In March 2025, together with the first package of survey data, a pioneering catalogue of approximately 500 candidates for strong galaxy-scale gravitational lenses was also published, found in only a very small part of the then-available dataset. That result did not arise only from a classic astronomical inspection of images, but from a combination of computer models, the work of citizen scientists, and expert verification by researchers. In other words, it turned out that the human eye, when well guided and supported by machine learning, still plays a crucial role in finding objects that automation alone does not always reliably recognise.
Now the bar has been set much higher. According to current information from the Space Warps – ESA Euclid project, this new phase uses previously unpublished Euclid images that will only become part of the first major data release in autumn 2026, known as Data Release 1 or DR1. The team states that machine-learning algorithms, further improved on the basis of earlier results and human classifications, examined about 72 million galaxies from the DR1 area. From this enormous set, the most likely candidates were selected, namely hundreds of thousands of the most interesting image cutouts that are now undergoing human verification. It is precisely at this stage that volunteers become involved, helping to identify arcs, rings, and other signs of strong gravitational lensing.
Such an approach is not only a practical solution for an enormous amount of data, but also an example of how modern science increasingly works: at the intersection of institutional infrastructure, artificial intelligence, and public participation. During its mission, Euclid sends about 100 gigabytes of data per day, and during the six-year programme it should observe more than 1.5 billion galaxies, out to distances of approximately 10 billion light-years. At such scales, every additional layer of filtering becomes necessary. Artificial intelligence can quickly sift through an enormous mass of records, but human observers still remain important for recognising unusual patterns, borderline cases, and phenomena that do not always follow expected patterns.
Why strong gravitational lenses are so important
Behind the appealing images of coloured galactic arcs lies serious scientific value. Strong gravitational lenses enable researchers to estimate the total mass of galaxies and galaxy clusters, including invisible dark matter. Since the distribution of mass determines how light will be bent, analysis of the shape and geometry of a lens can reveal how much matter is present in the observed system and how it is distributed. This is particularly important because most of the matter in the Universe cannot be observed directly with light, but its gravitational action can be measured precisely with methods such as these.
Gravitational lenses also have another major advantage: they serve as natural telescopes that amplify the light of even more distant objects. Because of this, astronomers can peer deeper into the Universe and study galaxies that would otherwise be too dim or too small for detailed analysis. In that sense, every new lens is not just another astronomical entry in a catalogue, but also a potential window into the earlier history of the Universe. The larger and higher-quality the sample of lenses, the more precise and statistically reliable the analyses of galaxy evolution, the distribution of dark matter, and the influence of dark energy on the accelerated expansion of the Universe.
The Euclid mission was primarily designed to answer precisely those big questions. The two key approaches on which it is based are weak gravitational lensing, which observes tiny statistical distortions in a large number of galaxies, and baryonic acoustic oscillations, which serve as a cosmic ruler in the analysis of the expansion of the Universe. But strong gravitational lenses provide an additional, highly valuable type of information. They offer more direct and often visually clearer examples of the action of gravity, while also serving as an independent check of the models used to describe the distribution of mass and the dynamics of cosmic expansion.
Euclid’s advantage: wide, deep, and exceptionally sharp
To find gravitational lenses, it is not enough to have only a sensitive telescope. A combination of wide sky coverage and very high resolution is also needed. This is exactly where Euclid has a major advantage. ESA’s telescope is designed to image enormous areas of the sky in a relatively short time while providing a very sharp picture in the visible and near-infrared range. Such a combination makes it possible to see in a single frame both huge clusters of galaxies and very subtle structures such as thin arcs that reveal the presence of gravitational lensing.
Euclid was launched in July 2023, and it began routine scientific observations on 14 February 2024. The mission is planned for six years, during which it should create the most extensive three-dimensional map of the Universe to date. ESA states that during this period Euclid will map approximately one third of the sky and track the shapes, distances, and motions of an enormous number of galaxies. The first published results have already shown that this is not just another space telescope, but an instrument that fills the gap between a “wide view” and high precision, which is crucial for the search for rare phenomena.
This was also seen in February 2025, when the discovery of an Einstein ring around the galaxy NGC 6505 was announced. According to ESA, it is a galaxy about 590 million light-years away, while the source whose light is being bent lies much farther away, at about 4.42 billion light-years. Such examples clearly show why the public tends to perceive gravitational lensing almost cinematically, but also why scientists consider it so valuable: in one scene, one simultaneously sees the geometry of space, the distribution of mass, and light from the deep cosmic past.
What the work of a citizen scientist looks like
Participation in the Space Warps project is designed to be simple and accessible to the general public. Volunteers examine small cutouts of Euclid’s images and answer whether they see features that might indicate strong gravitational lensing. The task is conceived to be quick, because most images will not contain a lens, precisely because such systems are rare. Still, when enough suspicious candidates appear among hundreds of thousands of images, the shared assessments of a large number of participants can greatly help researchers isolate the most promising targets for more detailed analysis.
This working model has already proven successful in practice. In earlier Euclid campaigns and related projects, citizens, together with algorithms and researchers, contributed to the discovery of hundreds of new candidates. Zooniverse, the platform on which the project takes place, states that the new round of the search was reactivated on 21 April 2026 with never-before-seen Euclid data and the ambition to find more than ten thousand lenses. The very fact that the public is being given access to unpublished cutouts from a future major dataset shows how much importance the research team attaches to citizen science.
It is important to emphasise that citizens do not replace experts, but rather do what they are still exceptionally useful at: recognising patterns, noticing visual anomalies, and helping to “clean up” results previously generated by artificial intelligence. A machine can be fast and tireless, but it is not always sufficiently reliable when it needs to distinguish a real gravitational arc from a chance alignment, a spiral arm, an image artefact, or a glare effect. That is precisely why the combined approach delivers the best results.
What the new search could bring to astronomy
If researchers’ expectations are confirmed and the new Euclid campaign really does lead to more than 10,000 high-quality candidates for strong gravitational lenses, that would represent a major leap compared with the previous history of this field. Project leader Aprajita Verma from Oxford has emphasised that such a result would be many times greater than the number of lenses found during nearly half a century since the first discoveries of gravitational lensing. For astronomy, that would not mean only a larger catalogue, but also a new level of statistical power in analyses that rely on large samples.
A greater number of confirmed lenses would enable more detailed comparisons among different types of galaxies, more precise models of the distribution of dark matter, and better calibration of the methods used to estimate the mass of galactic systems. In addition, a larger sample increases the chance that extremely rare or unusual examples will be found among the candidates, such as very regular Einstein rings, systems with multiple background sources, or lenses that help in the study of very distant and early galaxies. In a field where rare examples are often also the most valuable, expanding the search to hundreds of thousands of candidates opens space for real surprises.
There is also a broader aspect to this story. At a time when scientific projects increasingly rely on enormous data flows, Euclid and Space Warps show that the public can have a concrete role in top-level research. This is not symbolic “popularisation of science”, but a real contribution to the discovery process. When a citizen sits down at a computer and marks a possible gravitational arc, he is participating in the filtering of data from a mission that is trying to answer some of the hardest questions of contemporary physics: what the Universe is made of, how its structure evolved, and why its expansion is accelerating.
An early look into the future DR1 and a view toward autumn 2026
The current campaign carries particular weight because it concerns data that have not yet been publicly released. According to information on the project pages and Euclid’s data infrastructure, the first major Euclid Data Release 1 is expected on 21 October 2026. Until then, Space Warps participants have a rare opportunity to peek into part of the future dataset before its wider scientific and public distribution. This makes the project attractive not only to space enthusiasts, but also to everyone interested in what science looks like in real time, before the results become part of official catalogues and papers.
That is precisely why the search for gravitational lenses in Euclid’s images has a double value. On the one hand, it is serious scientific work that could significantly expand today’s understanding of dark matter, dark energy, and gravity. On the other hand, it is a rare opportunity for the public to participate in discovering phenomena that literally show how the Universe bends its own stage. At a moment when ESA’s telescope continues tirelessly to map the deep Universe, and the new round of Space Warps moves through hundreds of thousands of candidates from 72 million examined galaxies, the search for these cosmic “magnifying glasses” is becoming one of the most open and ambitious citizen-science actions in today’s astronomy.
Sources:- ESA – Euclid opens data treasure trove, offers glimpse of deep fields – official announcement about the first package of survey data, deep fields, 26 million galaxies, and the first catalogue of approximately 500 candidates for strong gravitational lenses.- ESA – Euclid discovers a stunning Einstein ring – official data on the Einstein ring around the galaxy NGC 6505 and an explanation of the scientific significance of gravitational lensing.- ESA – Euclid overview – an overview of the mission’s goals, launch date, start of routine observations, mission duration, and observational reach.- Zooniverse – Space Warps: ESA Euclid – current project description, information on the relaunch on 21 April 2026, the estimate of more than 10,000 new lenses, and the processing of 72 million galaxies in the DR1 area.- Euclid Consortium – Space Warps: Euclid – the citizen-science context, how to participate, the earlier campaign with 100,000 cutouts, and an explanation of the collaboration between people and algorithms.- ESA – Euclid calling: downloading the Universe – information on the amount of data the mission sends to Earth, about 100 GB per day.- Euclid Cosmos – Euclid Data Release 1 – the date of the expected first major DR1 data release, planned for 21 October 2026.
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