You may have heard of this phenomenon already but it’s still amazing to see it in action! The image here, captured by the Hubble Space Telescope and shared by NASA on Nov. 17, 2020, shows not individual stars but rather entire galaxies, each of them billions of light-years away from Earth. The brightest ones at the center comprise a cluster of galaxies, and the combined gravity of all the mass contained within that cluster warps spacetime so much that an even more distant galaxy, which would otherwise appear to us as a face-on disk, ends up looking like an elongated curved “smile” because of how severely its light gets bent as it passes the cluster on its way to Earth. Voila—gravity!
This effect, called gravitational lensing, was first predicted by Einstein’s general theory of relativity in 1915. Today, astronomers can use it to get a better look at objects—like galaxies—that lie at distances that would have been too far to image very well but because of a chance positioning of very massive objects like galactic clusters, which contain not only lots of gas, dust, and bright stars but also enormous haloes of dark matter, can be seen in detail much better…albeit warped quite a bit.
The gravitationally-lensed galaxy here is called SDSS J090122.37+181432.3 (sorry, it hasn’t been given a more poetic name yet) and is about 11 billion light-years away. It was identified in 2009 as part of the Sloan Bright Arcs Survey.
The image above has been cropped and rotated from its original north-up orientation.
This just shows how even though light travels through space, when space itself becomes distorted (as it does wherever there are massive objects) the light’s path also gets altered along with it.
In some cases, the light from distant galaxies can be bent into nearly a complete ring by the gravity of a closer galaxy lying in front of it, from our point of view.
The video below shows how light from the Whirlpool Galaxy (M51), which is “only” 23 million light-years away, would appear if it were gravitationally lensed by a cluster of galaxies that happened to be between it and us: