The results, published today in Science, show that the satellite galaxies surrounding Centaurus A, a well-known and relatively nearby galaxy 13 million light-years away, are orbiting not only in a single plane, but in a nice, orderly fashion as well. Such observations confirm what astronomers have already seen around our own Milky Way and the Andromeda Galaxy, but fly in the face of the standard cosmological model, which say that such systems should be rare — as in, 0.5 percent of galaxies. But at three for three, astronomers have seen it in 100 percent of systems, instead.
Centaurus A is an ideal object around which to study satellite galaxies because its satellites appear arranged neatly on a plane that is perpendicular to the galaxy itself, and face-on when we see it from Earth. That means any Doppler shifting of the light received from the satellite galaxies due to their motion is from their motion around the galaxy’s center, rather than overall motion toward or away from us. Out of 16 satellite galaxies observed, 14 are rotating together around the center of the galaxy. This is consistent with the findings when astronomers observe satellites around the Milky Way and Andromeda.