Is the Universe smiling at us? Yes and no.
There are two things going on in the picture above. The first is a type of pareidolia (the tendency to see faces in things), and the second is gravitational lensing (a prediction of Einstein’s theory of general relativity).
You can think about gravitational lensing like a cosmic version of eyeglasses floating out in space. But instead of a glass lens, thicker in some places than others, you have matter and dark matter clustered in some places more than others. Just as the light from your computer right now is being refracted as it passes through the lenses in your eye and/or the lenses in your glasses, the light from distant galaxies is refracted (or bent) as it passes through the matter around massive galaxies and galaxy clusters. The light from your computer is focused on your retina while the light from distant galaxies is focused (or collected) on a CCD in a telescope. [There is of course much more to it that this, but I’m just drawing a simply analogy. Gravitational lensing is described by relativity and the curvature of space-time.]
Note that for glass lenses, we can physically shape the glass to produce any image we want (think fun house mirrors and joke-shop glasses), but for the gravitational lenses we are given the image by the Universe and have to derive the physical shape (or properties) of the matter that produced it.
That’s where all the physics and math come in. Without going into too much detail, it’s analogous to the physics of optics, where you can develop a model lens and predict the images that will be produced depending on the location and size of the object you’re looking at. Astronomers then use observations of gravitationally lensed galaxies to derive the properties of the matter in the galaxy or galaxy cluster doing the lensing. Some special cases of precise alignment can produce multiple images of a single object, such as an Einstein ring or an Einstein cross.
In the Hubble image at the top of this post, each of the yellow eyes of the face are galaxies in the foreground that are refracting (or bending) the light from a distant background galaxy. That light is being lensed into the blue arcs that compose the smile and outline of the smile face. You read that right: those thin blue arcs are actually distorted images of a galaxy sitting far, far behind the yellow ones.
So next time you see the Universe smiling, I hope you’ll think about what’s behind that smile, because in my book, gravitational lensing is so much cooler than pareidolia. Here’s some geek that takes much less lensing to enjoy: Keep on geeking! @Summer_Ash, In-house Astrophysicist
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