When you first look at it, you think it might be a flaw in the image.  After studying it for a while, you realize it proves the existence of black holes, dark matter, and the warping of the fabric of space.

Light Warping Around Mass - NASA/ESA

The ring-like distortion effect on an image you see in gravitational lensing is referred to as Einstein Rings, mostly because Einstein predicted and quantified their existence in 1912.  We’ve talked about gravitational lensing before, specifically in this post discussion on gravitational lensing used to prove the existence of dark matter.

What basically happens is that as light travels toward you, if there is something of respectable mass between you and the light source, the light will bend around it in response to its gravity.  Science realized that sometimes they were looking at light bending around something they couldn’t see.  Something of extremely large mass.

Light waves, left alone, will travel in a straight path away from its source.  It doesn’t bend and warp on its own, but it will warp around a body of mass large enough to act on it. We see that as a distortion in the image.  There are several different types of distortion we will see, and an Einstein Ring is just one.  The Ring occurs when the mass source lines up “perfectly” between us and the light source.  The more complete the Ring, the more “perfect” the line up.  The Hubble Space Telescope found the first complete Ring in 1998.

If you like it mathematically, this is what it looks like geometrically:

Image released to public domain - author discourages attribution

It’s been almost a century since Einstein first predicted this effect.  Using the Hubble ST to map the known Rings, science has reached a clearer understanding of the distribution of dark matter and energy around us, the nature of galaxies as distant as 11 bly, and the curvature of the known universe.  I think that’s pretty amazing.