What is an Einstein-ring?

An Einstein ring (also known as Einstein-Chwolson ring) is a feature that is observed when light from a distant galaxy, or a star that is on its way to Earth, passes from a massive object. Due to the effect of gravity, the light is diverted, thus it appears coming from different places. In the ideal scenario, where the original source, the lens, and the observer (i.e., we on Earth) are aligned, the light from the distant source appears as a ring.

Observations with both space based (i.e., Hubble Space Telescope) and ground based telescopes (e.g., Very Large Telescope), have given us the opportunity to study such structures and confirm what is expected by the theory of general relativity. Additionally, the lensing effect of the background source, an effect known as gravitational lensing, allows us to study objects that are too distant and faint to observe otherwise.

Note that bending of light due to gravity was predicted four years prior the publication of general relativity, while the ring effect was mentioned for the first time in 1924 as “halo effect”.

GAL-CLUS-022058s is located in the constellation of Fornax. This is the largest Einstein ring ever observed, and one of the most complete ever discovered. Due to its appearance it has been nicknamed the “Molten Ring”. It is the result of gravitational lensing by a foreground elliptical galaxy that is located four billion light years away.

Image: Composite image of GAL-CLUS-022058s taken with the Hubble Space Telescope. The image was created from both optical and near infrared data, using broadband filters that are centred at 555 nm (V-band, blue and green), 775 nm (I-band, green and red), and 1600 nm (H-band , red).  

Image Credit: ESA/Hubble & NASA, S. Jha. Acknowledgement: L. Shatz