Galaxies and clusters of galaxies can sometimes warp space-time around them in such a way that faint background objects appear suddenly magnified. This phenomenon, known as gravitational lensing, can turn those galaxies into wide arches and even rings, known as Einstein’s rings. Now, Hubble has spotted the largest one yet.
Gravitational lensing occurs when distant light is distorted by a massive object like a galaxy or galaxy cluster in between the observer and the light source. The gravitational pull of the object bends the light, creating odd looping curves, or even rings. GAL-CLUS-022058s is the largest and one of the most complete Einstein rings ever observed in the universe. The gravity of a galaxy cluster in the Fornax (The Furnace) constellation has created multiple images of a distant spiral galaxy. The images are twisted around the central spherical galaxy in the cluster, with the two main arches almost touching.
Given its peculiar ring-like shape and the fact that it is in the Fornax, the team that observed this cosmic alignment nicknamed it “The Molten Ring".
Gravitational lensing is not just a beautiful cosmic phenomenon and a vindication of Einstein’s theory of general relativity. It is also an important way for us to study what we can’t see in the universe, such as black holes and dark matter.
Dramatic effects such as the one seen with GAL-CLUS-022058s are known as strong gravitational lensing and for that, you have to have objects with a lot of mass in a relatively small space. That’s why black holes and galaxy clusters are the best places to look for them.
There is also weak gravitational lensing, where the light of distant galaxies is only slightly altered by the mass between us and them. And even more minute in effect is microlensing, which could be created by a passing star or exoplanet, where we don’t see the distortion but the amount of light is increased for a short time.
All these phenomena have been used to better understand gravity itself but they have also allowed observations and discoveries that wouldn’t have been possible without the magnification they provide.
Some researchers would like to bring this idea to the next level. The first test of Einstein’s theory of general relativity in 1919 measured the light of a distant star deflecting around the Sun. In 1936, Einstein’s estimated that the Sun itself could be used as a telescope with a gravitational lens by placing an observatory at a distance of 542 times further out than the Earth.
It has been recently estimated that if such a telescope is constructed, it could in theory see the surface of an exoplanet with a resolution of 25 kilometers (15 miles).