Do you ever feel that when you look at the sky, something is up there looking back at you?
This cosmic eye is an illusion. I mean, duh, it's not an eye. But it's not even really shaped like one! The shape itself isn't real.
The "pupil" of the eye is actually a galaxy about 2.2 billion light years from Earth. That's a fair bit! But it happens to sit almost directly between us and a much more more distant galaxy -- one that is 11 billion light years away. As the light from the background galaxy passes by the nearer one, the gravity of the nearer one bends the path of that light, twisting it in what's called a gravitational lens.
Arcs are common results of lensing. That's what you're seeing here; the distant galaxy image split in two, arcs surrounding the spherical galaxy between them. An eye!
So that's cool all by its lonesome. But of course there's more.
A gravitational lens does more than distort the background galaxy image. it also magnifies it and makes it brighter. That means it's easier to see, and easier to study. Usually, galaxies 11 frakkin' billion light years away are too dinky to see well, but this one is literally laid out for us to see. By studying it, astronomers have actually been able to detect rotation (not by seeing it move -- that would take millions of years -- but by taking spectra and measuring the Doppler shift of the material in the galaxy. The rotation indicates that what we're seeing here is a disk galaxy, young, but relatively normal, on its way to becoming a spiral galaxy much like our own!
It's like a picture of a toddler, a galaxy growing up. It's easily the best study of a distant galaxy ever made. And it's pushed pretty hard on the technology -- Hubble discovered the lens (and took the image above), and it took the 10-meter Keck telescope in Hawaii to observe the spectra in detail. But soon, much larger telescopes currently being planned will find more objects like this, and instead of this being a one-off object, we'll be able to build up a catalog of them. And when that happens, our own eyes will be able to stretch back in time and distance even better.
Oh, one more thing: if that eye looks familiar to people of a certain age, well, you're not alone. The Alan Parsons Project predicted this image back in June of 1982! Don't believe me? Look at the name of the album: "Eye in the Sky"!
I am the eye in the sky Looking at you I can read your mind I am the maker of rules Dealing with fools I can cheat you blind And I don't need to see any more To know that I can read your mind, I can read your mind
Image credit: NASA/ESA/AURA