Scientists have discovered an incredible new "Einstein Ring"—a type of intergalactic mirage formed when a massive galaxy warps the fabric of spacetime like a colossal lens.
The ring was spotted by the European Space Agency's Euclid mission around the galaxy NGC 6505 in the constellation Draco, which lies roughly 590 million light-years from Earth—basically in our backyard, cosmically speaking.
As light from a second, never-before-detected and unnamed galaxy some 4.42 billion light-years away passes through the lens created by NGC 6505 on its way towards us, it is distorted into a giant ring.
Launched in 2023, Euclid is a wide-angle space telescope developed to learn more about the history and expansion of the universe by studying the redshift of distant galaxies.
The first hints of the ring came from images taken during Euclid's early testing phase in late 2023. The spacecraft's high-resolution instruments made these observations possible.
This type of cosmic phenomenon is named after the famous theoretical physicist Albert Einstein, whose theory of general relativity proposed that objects with mass distort the fabric of spacetime—making such 'gravitational lensing' effects possible.
With a powerful enough lensing effect as produced by NGC 6505, multiple images of background galaxies are formed into arcs, producing an apparent ring.
Lenses that are less spherical and more elongated, in contrast, can produce a similar phenomenon called an Einstein Cross, in which four distinct images are produced around the lensing galaxy.
"An Einstein ring is an example of strong gravitational lensing," said Conor O'Riordan of Germany's Max Planck Institute for Astrophysics, lead author of the paper describing the discovery, in a statement.
He added: "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."
Lenses are useful because they can allow us to learn about both given background galaxies, as well as about how the universe is expanding between us and them.
Einstein rings may also allow us to indirectly probe dark matter—an invisible substance proposed to explain the odd way certain galaxies behave—which also contributes to gravitational lensing.
Euclid project scientist Valeria Pettorino added: "I find it very intriguing that this ring was observed within a well-known galaxy, which was first discovered in 1884."
NGC 6505, which is some 190,000 light-years across, was first observed by the American astronomer and prolific cataloguer of nebulae Lewis A. Swift on June 27, 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," said Pettorino.
As Euclid continues to study the cosmos, it will piece together a three-dimensional map of more than a third of the sky, encompassing billions of galaxies as far distant as 10 billion light years away.
Physicists will use this data to measure the properties of both dark matter as well as dark energy, an equally mysterious repulsive force proposed to explain the accelerating expansion of the universe.
By the end of its mission, Euclid is expected to have found some 100,000 strong gravitational lenses of various different types.
For us to better probe dark energy, the spacecraft will need to look for a more subtle type of "weak" gravitational lensing than Einstein Rings—one in which the background galaxies appear only slightly stretched or displaced, not completely distorted.
"Euclid is going to revolutionize the field with all this data we've never had before," O'Riordan concluded.
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Reference
O'Riordan, C. M., Oldham, L. J., Nersesian, A., Li, T., Collett, T. E., Sluse, D., Altieri, B., Clément, B., Vasan, K. G. C., Rhoades, S., Chen, Y., Jones, T., Adami, C., Gavazzi, R., Vegetti, S., Powell, D. M., Barroso, J. A. A., Andika, I. T., Bhatawdekar, R., ... Dannerbauer, H. (2025). Euclid: A complete Einstein ring in NGC 6505. Astronomy & Astrophysics, 694. https://doi.org/10.1051/0004-6361/202453014
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