Gravitational lensing twists distant galaxy into an Einstein Ring
Believe it or not, that blue horseshoe-shaped structure around that bright star is an entire galaxy, although it doesn’t really look anything like that. Its incredible twisted shape is a mirage created by a strange phenomenon called gravitational lensing.
Light isn’t immune to the force of gravity, and if it comes into contact with a large enough object - such as the combined mass of a large galaxy - it can become radically distorted. That’s what has happened here. The light coming from the galaxy in this image had to pass through another, much closer galaxy on its way to Earth. That light was twisted out of its original position, and the end result is that we see something radically different from the original image.
This is known as gravitational lensing, but the effect on display here is particularly unusual. Most of the time, lensing will simply redirect the light from the original source so that we see a pair of mirror images. But if the alignment of the gravitational lens is absolutely perfect, it will twist the light into a horseshoe shape like the one we see here.
This was all predicted in considerable detail seventy years ago by Albert Einstein - making this roughly the 30th most impressive thing he ever did that is still completely beyond most people’s comprehension. Today, structures like this are called Einstein Rings in his honor. They also serve an important function in modern astrophysics, as the extent of lensing can help us determine the total mass - and thus the amount of dark matter - in the foreground galaxy that created the lens effect in the first place.