Look at the image above. What do you see? An oval galaxy with weird spirals and a weird bulge in its middle? It’s two galaxies, many billions of light-years apart, combined into one by a rare cosmic phenomenon called an Einstein ring. It’s an optical illusion.
Inside The ‘Einstein Ring’
Published recently as the James Webb Space Telescope Picture of the Month, the image shows two galaxies that couldn’t be more different. In the middle is an elliptical galaxy belonging to a cluster called SMACSJ0028.2-7537. It appears as an oval-shaped glow around a greenish-blue core and is in the foreground (yet still between three and seven billion light-years from the Milky Way). Meanwhile, on the outskirts of that galaxy — but far behind it — is a galaxy whose spiral arms appear to stretch and wrap around the closer galaxy, forming a warped ring.
Gravitational Lensing Explained
The strange, exceedingly rare object was found using one of the strangest quirks of nature — a gravitational lens. It’s when the gravitational field of a foreground object is so intense that it distorts the space around it and bends the light from an object behind it into circular rings. The ring both reveals the existence of the background object and magnifies it. Gravitational lensing is the best way to infer the presence of incredibly distant objects and measure their mass.
The Bending Of Space Time
This deflection of light by gravitational fields is also known as an Einstein ring because Albert Einstein predicted it. His general theory of relativity describes the universe as 4D, with three dimensions in space and one in time. Relativity is about what happens when you introduce mass into the 4D universe — it curves space-time, with space-time controlling how mass moves. Gravity is a result of that. Therefore, everything with mass — including light — curves as they pass through curved space-time. As predicted by Einstein, the first complete Einstein ring was found in 1998 by the Hubble Space Telescope.
Wishing you clear skies and wide eyes.