Euclid, the European Space Agency’s explorer of the dark Universe, has made a remarkable discovery—right in our cosmic neighborhood.
Euclid embarked on its six-year mission to explore the dark Universe on 1 July 2023. Before the spacecraft could begin its survey, scientists and engineers on Earth needed to ensure all systems were functioning correctly. During this initial testing phase in September 2023, Euclid transmitted a series of images back to Earth. These images were intentionally out of focus, but within one of them, Euclid Archive Scientist Bruno Altieri noticed something intriguing—a hint of a rare phenomenon. Determined to investigate further, he took a closer look.
“I examine Euclid’s incoming data as it arrives,” explains Bruno. “Even from that first observation, I could see it. But as Euclid continued observing the area, we confirmed a perfect Einstein ring. For someone with a lifelong interest in gravitational lensing, this was an incredible discovery.”
The Einstein Ring, a rare and striking phenomenon, was hiding in plain sight within a nearby galaxy. This galaxy, NGC 6505, is located approximately 590 million light-years from Earth—a relatively short distance in cosmic terms. Yet, this was the first time the luminous ring encircling its center had been detected, thanks to Euclid’s advanced high-resolution instruments.
The ring itself is composed of light from a much more distant galaxy, which lies 4.42 billion light-years away. As the light from this remote galaxy traveled toward us, the gravitational field of NGC 6505 bent and magnified it, creating the spectacular Einstein ring. This distant galaxy had never been observed before and remains unnamed.
“An Einstein ring is a prime example of strong gravitational lensing,” explains Conor O’Riordan from the Max Planck Institute for Astrophysics in Germany, lead author of the first scientific paper analyzing the ring. “Strong lenses are both rare and scientifically valuable. This one is particularly special because of its proximity to Earth and the nearly perfect alignment that makes it so visually stunning.”
Albert Einstein’s general theory of relativity predicts that massive objects bend light, effectively acting as cosmic lenses. The more massive the object, the stronger the lensing effect. This allows astronomers to observe distant galaxies that would otherwise remain hidden. When the alignment is just right, the distant galaxy’s light forms a striking ring around the foreground object, creating an Einstein ring. These rings serve as crucial tools for studying the expansion of the Universe, the effects of invisible dark matter, and the impact of dark energy.
“It is fascinating that this ring was found in a well-known galaxy first discovered in 1884,” notes Valeria Pettorino, ESA Euclid Project Scientist. “Astronomers have been studying this galaxy for a long time, yet this ring had never been observed before. This highlights Euclid’s power to uncover new phenomena even in familiar regions of space. This discovery is incredibly promising for the future of the mission and showcases Euclid’s impressive capabilities.”
By charting the Universe’s evolution over cosmic history, Euclid will enhance our understanding of gravity, dark matter, and dark energy. The telescope aims to map more than one-third of the sky, capturing billions of galaxies up to 10 billion light-years away. Scientists anticipate discovering around 100,000 strong gravitational lenses. Finding such a spectacular and nearby Einstein ring so early in the mission is remarkable. Until now, fewer than 1,000 strong lenses had been identified, and even fewer had been imaged with such high resolution.
“Euclid is set to revolutionize the field,” says Conor. “With the unprecedented volume of data it will provide, we are entering a new era of discovery.”
While this Einstein ring is an exciting find, Euclid’s primary mission focuses on detecting the more subtle effects of weak gravitational lensing, where background galaxies appear slightly stretched or displaced. To achieve this, scientists will analyze billions of galaxies. Euclid officially began its comprehensive sky survey on 14 February 2024, steadily constructing the most extensive 3D map of the Universe to date. Such an extraordinary discovery so early in the mission signals that Euclid is on track to unveil many more cosmic secrets.
