The Euclid space telescope has captured a rare phenomenon called an Einstein ring that reveals the extreme warping of space by a galaxy’s gravity.
The dazzling image shows a nearby galaxy, NGC 6505, surrounded by a perfect circle of light. The ring gives a glimpse of a more distant galaxy, sitting directly behind NGC 6505, whose starlight has been bent around the foreground galaxy.
“This is a beautiful, extraordinary, thrilling and lucky find in our first data,” said Prof Stephen Serjeant, an astronomer at the Open University. “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’s general theory of relativity predicts that light will bend around massive objects in space, meaning that galaxies can act as vast lenses. Einstein rings are a powerful tool for astronomers because they reveal objects that would otherwise be obscured from view and indicate the mass of the intermediate galaxy – including any hidden mass in the form of dark matter.
In this case, astronomers estimate that the foreground galaxy comprises roughly 11% dark matter. This is a relatively small fraction given that dark matter is believed to dominate the overall mass content of the universe.
Uncovering the secrets of dark matter and dark energy, which together make up 95% of the universe, is the central aim of the European Space Agency’s €1bn (£850m) mission. Ultimately the telescope, which can detect galaxies out to 10bn light years, is aiming to create the largest cosmic 3D map ever made. This will allow astronomers to infer the large-scale distribution of dark matter and reveal the influence of dark energy, a mysterious force that is accelerating the expansion of the universe.
The telescope will capture images of objects up to 10bn light years away, but the latest image shows its unmatched ability for razor-sharp observations is revealing new structures in the nearby universe, too. The NGC 6505 galaxy is about 590m light-years from Earth – a stone’s throw away in cosmic terms – and the unnamed background galaxy is 4.42bn light years away.
“I find it very intriguing that this ring was observed within a well-known galaxy, which was first discovered in 1884,” said Dr 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.”
