NASA spots "galactic cannibalism" served rare

Galaxies feasting on their smaller siblings may sound like the stuff of science-fiction, but NASA has captured a surprisingly rare example on camera. The shot, of elliptical galaxy NGC 3923 situated more than 90 million light years away from Earth, was snapped by the Hubble Space Telescope, though it's not the distance that makes it special. Instead, it's the fact that not only is it a so-called "shell galaxy", but one which shows unusual symmetry that has NASA's astronomers curious.

Shell galaxies are formed when concentric rings of stars enclose an inner-galaxy. Described by NASA as being similar in structure to an onion, exactly how they form isn't certain, but it's believed to be down to a type of cannibalism on a galactic scale.

A larger galaxy is presumed to swallow a smaller one, with ripples eventually pulsing out from their common center. Those oscillations lead to the shells of stars surrounding the newly-combined galaxy.

NGC 3923, which is found in the constellation of Hydra, has more than twenty such shells. While the onion formation isn't rare in and of itself, NASA says, it's nonetheless far less common to find such a symmetric arrangement of the layers.

Some sort of skewed layout is more likely, as the ripples oscillate out unevenly.

All the same, there's no worry of a larger galaxy chomping through our own Milky Way at any point. So far, there's no evidence that galactic cannibalism occurs to spiral galaxies like our own.