An Einstein ring is created when light from a more distant galaxy or star is bent when it passes a closer massive object closer to Earth. Due to the gravitational lensing, the light from the distant galaxy appears as a arc or a ring.If the source, lens object and observer are all in perfect alignment the light appears as a ring.
The bending of light by a gravitational body was predicted by Albert Einstein in 1912.
Einstein rings are a rich laboratory for studying the expansion of the Universe, detect the effects of invisible dark matter and dark energy, and investigate the background source. Hundreds of gravitational lenses are currently known.
Einstein Ring – the Cosmic Horseshoe
Cosmic Horseshoe – a closer red galaxy with an Einstein ring image of distant blue galaxy
The above image is from Hubble Space Telescope’s Wide Field Camera 3 data taken in 2010 and 11. The foreground galaxy, LRG 3-757, is found to be extremely massive, with a mass a hundred times that of our galaxy.
The Cosmic Horseshoe was first identified by Belokurov et al. (2007) as part of the Sloan Digital Sky Survey. It consist of a closer red galaxy (LRG) surrounded by an Einstein ring image of much more distant blue galaxy. The central LRG 3-75 galaxy is about five-and-a-half billion light-years away.
LRG 3-757 is approximately 100 times more massive than the Milky Way and is among the most massive galaxies ever identified.
Results in a paper published in February 2025 of the Hubble data reveals the presence of an Ultra-Massive Black Hole (UMBH) in the foreground galaxy with a staggering 36 billion solar masses. https://arxiv.org/pdf/2502.13788
Einstein Ring in relatively close galaxy discovered by Euclid space telescope
Galaxy NGC 6505 with Einstein ring
Expanded view of Einstein ring in NGC 6505
The Euclid telescope captured a ring of light surrounding the centre of the galaxy NGC 6505. The image also includes the extended halo of the galaxy, nearby stars and other distant galaxies.
Galaxy NGC 6505 is around 590 million light-years from Earth, “a stone’s throw away in cosmic terms”. But this is the first time that the ring of light surrounding its centre is detected, thanks to Euclid’s high-resolution instruments. This background galaxy is 4.42 billion light-years away https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_discovers_a_stunning_Einstein_ring
ESA’s Euclid mission is a six-year mission designed to explore the composition and evolution of the dark Universe. The Euclid space telescope will create a great map of the large-scale structure of the Universe across space and time by observing billions of galaxies out to 10 billion light-years, across more than a third of the sky. It launched on 1 July 2023 to its destination at the Sun-Earth Lagrange point 2, 1.5 million km from Earth.