European Space Agency's (ESA) Euclid space telescope has captured an image of an extremely rare cosmic phenomenon known as an Einstein ring. This stunning visual showcases a ring of light encircling the centre of the galaxy NGC 6505, which is around 590 million light-years from Earth in the constellation Draco. Though it may sound far, in astronomical terms, the galaxy lies in our 'cosmic backyard', the details of which have been published in a study in the journal Astronomy and Astrophysics on February 10, 2025.
The ring is made up of light coming from another galaxy almost 4.42 billion light years away and what we see from Earth is distorted by gravity. The distant galaxy is yet to be observed and therefore has not been named yet.
Euclid archive scientist Bruno Altieri first noticed a hint of the Einstein ring, way back in 2023 while going through images from the spacecraft's early testing phase.
"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," said Mr Altieri.
"For me, with a lifelong interest in gravitational lensing, that was amazing."
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What is Einstein ring?
Named after Albert Einstein, one of the greatest scientists to have ever lived, his theory of relativity states that light will bend around objects in space, so that they focus the light like a giant lens, with this effect being bigger for massive galaxies.
Based on this theory, Einstein ring is nothing but light from a distant galaxy bending to form a ring that appears aligned with a foreground object. The strong gravitational field produced by the lens galaxy distorts the structure of space-time in its neighbourhood, and this not only attracts objects which have a mass but also bends the paths of light.
"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."
When the two galaxies are exactly aligned, the image of the more distant galaxy is converted into an almost perfect circle which surrounds the lens galaxy.
The phenomenon helps scientists explore different aspects of the universe, including its expansion, the existence and effects of dark matter and dark energy.
