My personal take on what's going on within our Event Horizon. Mostly astronomical, often cosmological, usually quite grumpy.
Geraint, I hope I'm understanding this correctly. Is the main "surprise" in this research, that the dwarf galaxies are rotating toward and away from us? If this is correct, wouldn't any object large or small that becomes part of a greater entity (a galaxy)be held by gravity and therefore orbit around the core, in varying distances?
Hi John - the surprise is that there is ordered rotation in the population, so this subset of dwarfs is orbiting like the planets of the solar system, rather than the long-term comets, which are at any angle. The latter is what we would expect for the dwarf population.
Are they orbiting an "unseen" centre?..or are they orbiting each other (in a planetary motion) due to the gravitational effect they have on each other?
The main force the dwarf will feel will be from the Andromeda galaxy, and the dark matter halo in which they reside. The force from each other is relatively small, unless they get close together.