Inside an oval shaped galaxy, European astronomers detect nearest Einstein ring using Euclid telescope

Astronomers have identified the nearest known Einstein ring, a rare gravitational lensing phenomenon where light from a distant galaxy is bent by the gravitational field of a closer galaxy. Initially thought to be a single galaxy, the object was first observed more than a century ago but has now been confirmed as a gravitational lens.

Such galactic lenses were predicted by Albert Einstein in 1936 as part of his general theory of relativity. At the time, he believed they would be too difficult to observe. However, with modern telescopes, such phenomena can now be detected. “It was there all along, but we had no idea,” said Thomas Collett from the University of Portsmouth, UK.

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The Einstein ring was discovered when Collett and his team studied NGC 6505, an oval-shaped galaxy located around 600 million light-years from Earth. The galaxy, first documented in 1884, was found to be bending the light from a second galaxy approximately 6 billion light-years away.

The discovery was made using data from the European Space Agency’s Euclid telescope, which is surveying billions of galaxies across a third of the night sky. Team member Bruno Altieri noticed the Einstein ring while validating early test data. “There was this abundantly obvious Einstein ring. There are not many things in the universe that can produce a ring like this,” Collett said.

The ring appears exceptionally bright compared to other known Einstein rings. Its relative proximity to Earth and the imaging capabilities of Euclid make it easier to distinguish the four images of the distant galaxy. The faint orange glow surrounding the ring represents the lensing galaxy.

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Theory of Relativity 

This discovery provides an opportunity to test Einstein’s theory of general relativity. Researchers can measure the mass of the lensing galaxy in two ways—by analysing how the light bends and by observing the velocity of its stars. Einstein’s theory predicts these values should be the same, so any discrepancy could indicate a need to modify existing gravitational models.

When the team calculated the mass of the lensing galaxy, they found it to be slightly higher than expected based on the estimated number of stars it contains. This discrepancy may be due to dark matter clustering at the galaxy’s centre, according to Frédéric Dux from the European Southern Observatory. However, further observations of similar lenses will be required to confirm this hypothesis.