Scientists at the University of Portsmouth have led the discovery of more than 15,000 strong gravitational lenses in the first major data release from the European Space Agency's Euclid mission - the largest catalogue of its kind ever produced, bigger than all previous catalogues combined.
The lens search was led by researchers from the University of Portsmouth's Institute of Cosmology and Gravitation , including Professor Thomas Collett, Natalie Lines, Philip Holloway and Tian Li, working as part of the Euclid Consortium.
Strong gravitational lenses are extremely rare. They form when light travelling to us from a distant galaxy is significantly distorted by the gravity of a foreground galaxy, bending it into arcs and rings. Because the amount of distortion depends on the total mass of the foreground galaxy - visible and invisible - lenses are one of the few tools that let astronomers directly measure dark matter.
An artist impression of ESA's Euclid mission in space. Credit: ESA. Acknowledgement: Work performed by ATG under contract for ESA.
Professor Thomas Collett , from the University of Portsmouth's Institute of Cosmology and Gravitation, said: "Before Euclid, astronomers had found only a few hundred strong lenses in decades of searching. Finding 15,000 in the first year's data alone changes what we can do with them. This result is down to the hard work of the team who built and ran the lens search, as well as the efforts of our international collaborators. Thanks to them, instead of studying a handful of lenses one at a time, we can now treat them as a population and ask much sharper questions about dark matter and the expansion of the Universe."
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. This new release of data captures the light of more than a billion objects and covers an area of sky as big as 9500 full Moons.
Before Euclid, astronomers had found only a few hundred strong lenses in decades of searching. Finding 15,000 in the first year's data alone changes what we can do with them. This result is down to the hard work of the team who built and ran the lens search, as well as the efforts of our international collaborators.
Thomas Collett , Professor of Astrophysics
Natalie Lines, University of Portsmouth PhD student and member of the Euclid Consortium, said: "Strong lensing provides unique insight into the dark Universe, allowing us to 'weigh' individual galaxies, including their invisible dark matter, and explore how the Universe is expanding. Over 10 years ago, we forecast that Euclid would revolutionise the field of strong lens discovery. That day is finally here."
The new data release from Euclid, named DR1-Foundation, comprises around 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 gives scientists the puzzle pieces they need to begin constructing a detailed 3D map of the cosmos - crucial to solve the many mysteries of the dark Universe (including dark energy, dark matter, and the cosmic web).
Strong lenses collage. Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by N. Lines and T. Li
The data are accompanied by spectra and images, including large sky mosaics. "These are far more than beautiful pictures; today marks a scientific milestone in our study of the cosmos," explained ESA's Director of Science, Professor Carole Mundell.
"This major Euclid data release represents the largest space-based survey of its kind, laying the foundation of future discovery in a new regime for astronomy and demonstrating the excellence of European technology, science and international collaboration."
Today's release is the first to demonstrate Euclid's abilities 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. DR1-Foundation reveals unprecedented numbers of cosmic objects, and includes:
• Over 900 million galaxies
• Around 15 000 strong gravitational lensing candidates
• Over 60 million quasars, the brilliant cores of distant galaxies
• The spectra from more than 160 million sources
• Euclid Wide Survey results from 1900 deg² of sky - a total of 1.7 million GB of data
While enormous, the dataset only covers about 14% of the total sky area Euclid will survey. The full Data Release 1, to come in mid-2027, will build on today's release and add more crucial parts to the cosmic puzzle, including observations of weak lensing to complement the strong ones, and calculations of how galaxies and galaxy clusters fit into the cosmic web.
