Galaxies eat each other like I eat post-Halloween sale candy. That is to say, voraciously. Astronomers have put together the evidence for such "galactic cannibalism" for years, and a neat spiral hidden inside an elliptical galaxy is the latest interesting evidence.
Meet Centaurus A, also known as NGC 5128, our nearest massive elliptical galaxy. It is well known for being a nearby active galaxy, meaning that there is material actively falling onto the central supermassive black hole, which causes a pretty display in all different wavelengths of light. Using the Sub-Millimeter Array (SMA) astronomers have discovered that inside that elliptical is a tiny spiral of rotating gas, with properties similar to the arms of a spiral galaxy.
This is another complication in the canonical "Hubble tuning fork" classification of galaxies. When Edwin Hubble first started classifying galaxies by their shapes, they fell into two general types, elliptical and spirals, with the spiral being further divided into barred and un-barred. Classical thinking about galaxies was that spirals were full of gas, active star formation, and young blue stars, whereas those old elliptical galaxies are "red and dead," not showing signs of recent star formation.
But the case is, as usual, never so simple. On closer inspection, many ellipticals have groupings of stars or gas and dust that rotate in a disk, hinting at a recent act of galactic cannibalism. That is, some smaller galaxy fell into the large elliptical and was gobbled up, but some of the new material can be distinguished by its motions, different from the rest of the big galaxy.
Centaurus A already has a prominent, visible dust lane and signs of recent activity. Also, because it is so close, a mere 12 million light years away, this is a perfect candidate for studying these hidden disks within ellipticals.