In galaxy-galaxy strong gravitational lensing, light from a distant galaxy is bent and magnified by the gravitational field of a nearby galaxy, creating multiple images of the distant galaxy. When the distant galaxy is not a single point of light and is near the center of the lens galaxy, an “Einstein ring” is formed. Both Einstein rings and lensed point sources are scientifically valuable and have been used in many applications.
Euclid began its six-year mission to explore the dark Universe on 1 July 2023. Before starting the survey, scientists and engineers had to ensure everything worked properly. In September 2023, during early testing, Euclid sent some deliberately out-of-focus images back to Earth. Euclid Archive Scientist Bruno Altieri noticed something special in one fuzzy image and looked closer.
After looking at the data, the team could see a perfect Einstein ring – an extremely rare phenomenon- hiding in plain sight in a galaxy not far away.
The galaxy, NGC 6505, is around 590 million light-years from Earth, which is relatively close in cosmic terms. Thanks to Euclid’s high-resolution instruments, this is the first time that the ring of light surrounding its center has been detected.
This ring around the foreground galaxy is created by light from a much more distant, brighter galaxy located 4.42 billion light-years away. As the light from this background galaxy travels towards us, it gets distorted by the gravitational field of NGC 6505, creating what is known as an “Einstein ring.”
ESA’s Euclid celebrates first science: New views of the Universe
Valeria Pettorino, ESA Euclid Project Scientist, said, “I find it very intriguing that this ring was observed within a well-known galaxy, which was first discovered in 1884. 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.”
By studying the Universe’s expansion and formation throughout its cosmic history, Euclid will shed light on the role of gravity and the nature of dark energy and matter. The space telescope will map over a third of the sky, observing billions of galaxies up to 10 billion light-years away. It is expected to discover around 100,000 strong gravitational lenses, which is astonishing compared to the fewer than 1,000 strong lenses known before, most of which were not imaged at high resolution.
It is remarkable to find such a spectacular and close-up strong lens. Conor, one of the researchers, emphasizes the impact of Euclid, stating, “Euclid is going to revolutionize the field with all this data we’ve never had before.”
Although this Einstein ring is stunning, Euclid’s primary mission is to search for the subtler effects of weak gravitational lensing, where background galaxies appear slightly stretched or displaced. To detect these effects, scientists need to analyze billions of galaxies. Euclid began its detailed sky survey on 14 February 2024 and is gradually creating the most extensive 3D map of the Universe yet. Such an incredible discovery early in its mission indicates that Euclid is on track to uncover many more hidden secrets.
Journal Reference:
- C. M. O’Riordan, L. J. Oldham, et al. Euclid: A complete Einstein ring in NGC 6505⋆. Astronomy and Astrophysics. DOI: 10.1051/0004-6361/202453014
