Hubble captures a sublime “Einstein ring” created by distant galaxies
This image might look like someone left a coffee mug on a photograph of some Christmas lights, but it actually illustrates a fundamental part of our understanding of physics.
What you’re looking at is a picture filled with distant galaxies, and in the middle of the image is a particularly dense cluster of galaxies. So dense, in fact, the cluster is distorting spacetime and creating what’s known as an Einstein ring.
Among the many phenomena predicted in Albert Einstein’s theory of general relativity was something called gravitational lensing. Instead of travelling in three dimensions straight to a viewer’s eye, light from a distant source can become warped by the presence of an enormous body of matter, distorting spacetime and bending light as it travels to an observer.
In its most symmetrical form, this warping is known as an Einstein ring, and happens when there’s an exact alignment with whatever is emitting the light, the ‘lens’ of gravity that distorts spacetime, and the observer – in this case our old friend the Hubble Space Telescope.
The two bright dots at the very centre of the image are a dense cluster of hundreds of galaxies, poetically called SDSS J0146-0929. The purple arcs that make up the ring are a galaxy too, even further away, but its light has been distorted by the strong gravity of this dense cluster. It’s a bit like a magnifying lens has been placed between that background galaxy and the Hubble Space Telescope, except this gravitational lens actually bends spacetime.
This isn’t the first time an Einstein ring has been observed in action, although that honour also fell on the Hubble Space Telescope as part of a collaboration with the University of Manchester in 1998. Since then, these phenomena have been used to pinpoint extremely distant stars, and even to calculate the mass of a white dwarf star by the way it distorted the light of another star behind it. Let’s also not forget the “Cheshire Cat” Einstein ring, which looks like a smiling face.
This most recent image of an Einstein ring doesn’t unravel any extra secrets about our universe, but it’s a beautiful reminder that the expanse of space isn’t always what it first seems.
Image credit: ESA/Hubble & NASA/Judy Schmidt