Incredible Einstein Ring Seen By Euclid Mission On Well-Known Galaxy

The European Space Agency (ESA)’s Euclid Mission has been working over the last 18 months to understand what dark matter and dark energy really are. These are components of the universe whose existence is justified by observations and models, but we do not know what they really are. This quest is performed by Euclid, with extraordinary observations that deliver unusual stuff – like an extraordinary Einstein ring.

An Einstein ring is a gravitational lens phenomenon caused by the almost perfect alignment between a distant galaxy and a dense foreground object, in this case, an elliptical galaxy called NGC 6505. NGC 6505 is around 590 million light-years from us. Its enormous gravity warps space-time and so the light of a background galaxy 4.42 billion light-years away is warped into a ring.

“An Einstein ring is an example of strong gravitational lensing,” lead author Conor O’Riordan, of the Max Planck Institute for Astrophysics, said in a 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.”

The Einstein ring was discovered serendipitously and it came from one of the earliest science images collected by the telescope in September 2023, just weeks after its launch. Those observations were purposely out of focus (and a glitch actually created some beautiful images) but researchers were able to see what they were hiding immediately.

“I look at the data from Euclid as it comes in,” explained Euclid Archive Scientist Bruno Altieri. “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.”

Strong gravitational lenses, per se, are not the way that Euclid is trying to unravel the mystery of dark matter and dark energy, but they are excellent laboratories to test those hypotheses and Einstein’s relativity to the limit. Finding more of them is important, and it is even more curious to find one in a galaxy that has been known for over 140 years.

“I find it very intriguing that this ring was observed within a well-known galaxy, which was first discovered in 1884,” said Valeria Pettorino, ESA Euclid Project Scientist. “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.”

A paper describing the observations is published in the journal Astronomy & Astrophysics.

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