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Euclid space telescope discovers a stunning Einstein ring
14 February 2025
Euclid, the European Space Agency telescope whose massive optical camera was designed and built by an international team led by UCL researchers, has captured a rare phenomenon known as an Einstein ring which reveals the extreme warping of space caused by a galaxy’s gravity.
The ring turned out to be hiding in plain sight in a galaxy not far away. The galaxy, called NGC 6505, is around 590 million light-years from Earth, a stone’s throw away in cosmic terms. But this is the first time that the ring of light surrounding its centre has been detected, thanks to Euclid’s high-resolution instruments.
The ring around the foreground galaxy is made up of light from a farther out bright galaxy. This background galaxy is 4.42 billion light-years away, and its light has been distorted by gravity on its way to us. The far-away galaxy hasn’t been observed before and doesn’t yet have a name.
Professor Mat Page, based at UCL’s Mullard Space Science Laboratory, who is the current lead for the VIS (visible light) camera, said: “Astronomers have been imaging this galaxy for more than 100 years, but it took the super-high resolution of Euclid to reveal this amazing Einstein ring.
“The best images of the ring come from Euclid’s VIS camera, which was built by an international consortium led by UCL.”
Euclid blasted off on its six-year mission to explore the dark Universe on 1 July 2023. Before the spacecraft could begin its survey, the team of scientists and engineers on Earth had to make sure everything was working properly.
During this early testing phase, in September 2023, Euclid sent some images back to Earth. They were deliberately out of focus, but in one fuzzy image Euclid Archive Scientist Bruno Altieri saw a hint of a very special phenomenon and decided to take a closer look.
He said: “I look at the data from Euclid as it comes in. Even from that first observation, I could see it, but after Euclid made more observations of the area, we could see a perfect Einstein ring. For me, with a lifelong interest in gravitational lensing, that was amazing.”
Dr Conor O’Riordan, based at the Max Planck Institute for Astrophysics, Germany, and lead author of the first scientific paper analysing the ring, said: “An Einstein ring is an example of strong gravitational lensing.
“All strong lenses are special, because they're so rare, and they're incredibly useful scientifically. This one is particularly special, because it’s so close to Earth and the alignment makes it very beautiful.”
Albert Einstein’s general theory of relativity predicts that light will bend around objects in space, so that they focus the light like a giant lens. This gravitational lensing effect is bigger for more massive objects – galaxies and clusters of galaxies. It means we can sometimes see the light from distant galaxies that would otherwise be hidden.
If the alignment is just right, the light from the distant source galaxy bends to form a spectacular ring around the foreground object. These Einstein rings are a rich laboratory for scientists. Studying their gravitational effects can help us learn about the expansion of the Universe, detect the effects of invisible dark matter and dark energy, and investigate the background source whose light is bent by dark matter in between us and the source.
Valeria Pettorino, ESA Euclid Project Scientist, said: “I find it very intriguing that this ring was observed within a well-known galaxy, which was first discovered in 1884.
“The galaxy has been known to astronomers for a very long time. And yet this ring was never observed before. This demonstrates how powerful Euclid is, finding new things even in places we thought we knew well. This discovery is very encouraging for the future of the Euclid mission and demonstrates its fantastic capabilities."
By exploring how the Universe has expanded and formed over its cosmic history, Euclid will reveal more about the role of gravity and the nature of dark energy and dark matter. The space telescope will map more than a third of the sky, observing billions of galaxies out to 10 billion light-years.
It is expected to find around 100,000 strong lenses, but to find one that’s so spectacular – and so close to home – is astonishing. Until now, less than 1,000 strong lenses were known, and even fewer were imaged at high resolution.
Although this Einstein ring is stunning, Euclid’s main job is searching for the more subtle effects of weak gravitational lensing, where background galaxies appear only mildly stretched or displaced.
To detect this effect, scientists will need to analyse billions of galaxies. Euclid began its detailed survey of the sky on 14 February 2024 and is gradually creating the most extensive 3D map of the Universe yet.
VIS camera
The VIS (for Visible) instrument is a 609 megapixel optical camera. Its wide field of view means that, while it takes images that are nearly as sharp as the Hubble Space Telescope, it covers a much larger area of the sky – covering the same area in one day as Hubble covered over 25 years. Each image would require 300 high-definition TV screens to display. Over six years it will allow the shape of more than 1.5 billion galaxies to be measured.
The VIS camera was a pan-European project led by UCL’s Mullard Space Science Laboratory (MSSL). Its structure and calibration unit came from France, the shutter from Switzerland, and a processing unit was built in Italy. The core electronics, including its array of 36 CCDs (that convert photons into electrons), were built, tested and calibrated at MSSL. A team of MSSL experts are also supporting the operation of the VIS instrument in flight.
In addition, researchers at MSSL and UCL Physics & Astronomy are involved in processing and analysing Euclid’s data to see how it compares to mathematical models of the Universe.
Links
- The paper in Astronomy & Astrophysics
- Professor Mat Page’s academic profile
- Mullard Space Science Laboratory at UCL
- UCL News story – ‘Euclid space mission celebrates first science with sparkling cosmic views’
- UCL News story – ‘Euclid’s first images: the dazzling edge of darkness’
- UCL News story – ‘Space telescope to shed light on dark universe’
- UCL News story – ‘First-light images from Euclid-VIS’
- UCL Physics & Astronomy
- UCL Mathematical & Physical Sciences
Source
Images
- From top: Euclid image of a bright Einstein ring around galaxy NGC 6505. Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre, G. Anselmi, T. Li;
- Middle: Close-up of the Einstein ring around galaxy NGC 6505. Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre, G. Anselmi, T. Li
- Bottom: Infographic explaining how an Einstein ring is formed. Credit: ESA.
Media contact
Mark Greaves
E: m.greaves [at] ucl.ac.uk
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