Some neighbors you just don't want, and that applies if you are a galaxy as well. NGC 1316 looks to be one of those. It's a deep space Hannibal, based on evidence from the European Southern Observatory (ESO) that reveals traces of its past consumption of a spiral galaxy three billion years ago.
Galactic cannibalism is not rare. Indeed the favored theory of galaxy formation is that big galaxies got that way by eating up small ones. Nevertheless, in most cases the traces have been well hidden. This is not the case for NGC 1316, a lenticular (that is halfway between spiral and elliptical) galaxy 60 million light years away. Bad news for the smaller galaxy NGC 1317, which has the misfortune to live right next-door.
The extraordinarily complex dust lanes revealed in the Hubble image at bottom are one clue to NGC 1316's past. Another feature is the numerous small globular clusters that surround it. Large globular clusters surrounding a galaxy are thought to be the remnants of dwarf galaxies that have been stripped apart, but smaller ones are often prized baubles collected when large galaxies are eaten whole.
The final visible sign is the tidal tails – patches of stars ripped from their location within a galaxy and thrown into intergalactic space by the forces of the eaten and the eater interacting.
"All of these signs point to a violent past during which NGC 1316 annexed other galaxies and suggest that the disruptive behavior is continuing," an official ESO statement noted.
Astronomers have suspected that something was up with NGC 1316 since it was discovered to be the fourth brightest radio source in the sky at 1400MHz, dubbed Fornax A by radio astronomers after its constellation and brightness. These emissions are a product of the unusually large amount of gas and dust falling into the supermassive black hole at its heart. This is estimated as 130-150 million times more massive than the sun, or 30-40 times the size of the one in the center the Milky Way A galaxy that had not eaten such a large meal so recently would be in a more stable state, without the clouds of disrupted gas available to the central hole.
By combining extensive images from the archive of the MGP/ESO 2.2m telescope the ESO have produced this image of the two galaxies side by side. For those who prefer a little color and motion, you can close in on the pair in the video below.
So far NGC 1317 has managed to largely retain its spiral structure, but at such close range to a galaxy of this size it is only a matter of time before it to gets ripped apart. Interestingly, NGC1316 resembles a number of other galaxies at the center of large clusters, but sits at the edge of the Fornax Cluster.