Astronomers Discover Extremely Rare Einstein Ring in Early Euclid Telescope Data, Revealing Warped Space-Time

In September 2023, the European Space Agency’s (ESA) Euclid space telescope sent some images back to Earth during an early testing phase. While reviewing the pictures, astronomer and Euclid archive scientist Bruno Altieri found something incredibly rare: an Einstein ring circling a galaxy. The discovery was announced in a study published Monday in the journal Astronomy and Astrophysics.

“This is a beautiful, extraordinary, thrilling and lucky find in our first data,” Stephen Serjeant, an astronomer at the Open University in England and co-author of the study, tells the Guardian’s Hannah Devlin. “An Einstein ring as perfect as this is extremely rare. We get to see a background galaxy through the warped space and time of a very nearby foreground galaxy.”

Albert Einstein predicted in his theory of general relativity that the gravity of large centers of mass, such as galaxy clusters, could bend the light of other celestial bodies, acting as a gravitational lens. Sometimes, a structure’s light could become so warped that it appears multiple times (like a mirror image), or in the shape of a circle called an Einstein ring, depending on the perspective. Unfortunately, Einstein didn’t live to see his theory confirmed, when the first gravitational lens was detected in 1979.

Though Euclid is expected to detect around 100,000 strong gravitational lenses, astronomers currently know of fewer than 1,000, per an ESA statement.

“An Einstein ring is an example of strong gravitational lensing,” lead author Conor O’Riordan, an astrophysicist at the Max Planck Institute for Astrophysics in Germany, explains in the statement. “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.”

In this case, the Einstein ring appears around galaxy NGC 6505, which was first identified in 1884, according to the statement. At around 590 million light-years from Earth, NGC 6505 is relatively close, astronomically speaking. Beyond the galaxy, however, is another unknown bright galaxy 4.42 billion light-years away, and we see its light as ring-shaped as it’s warped by the gravitational force of galaxy NGC 6505 on its way to us.

Because of such gravitational lensing, astronomers can infer the presence of celestial structures that we would otherwise be unable to detect or see, such as dark matter. In fact, the Euclid mission aims to create a 3D map of more than one-third of the sky to survey the composition and evolution of the universe. This is expected to shed light on the role of dark matter and dark energy, mysterious substances that together make up about 96 percent of the universe. Scientists theorize that dark energy is responsible for the universe’s accelerating rate of expansion. In October, Euclid released the first section of its cosmic map.

Modeling gravitational lenses can reveal more information about the properties of dark matter, according to the paper. In this case, the team found that the central region of NGC 6505 contains about 11 percent dark matter—a much lower proportion than across much of the universe. This new, chance find suggests “the central regions of galaxies are truly peculiar,” study co-author Giulia Despali, an astrophysicist at the University of Bologna in Italy, tells Space.com’s Robert Lea.

“We would have expected about a one in three chance of finding something as spectacular as this over the whole survey,” study co-author Thomas Collett, an astrophysicist and cosmologist at the University of Portsmouth in England, tells New Scientist’s Alex Wilkins. “To find it in essentially the first, earliest data is spectacularly lucky. This is probably the prettiest lens we will find in the mission.”

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Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.