[By.Jove (Jove)]

Well, I can think of three possibilities which should be testable.

1. An artifact of the scope that took the image, and/or the processing. Easily confirmed by getting someone else to shoot same patch of sky independently with another rig. I doubt APOD would have published it without having it verified independently, which suggests....

2. The arcs have been there all along - but nobody noticed before. There are really deep wide field surveys such as the Palomar Schmidt plates that may show whether or not they were there years ago. The SDSS is searchable online...

Alternatively...

3. If it really wasn't there 2.5 months ago and really is there now, it would have to be wisps of interstellar fluff really close to, or maybe within the solar system. In which case another image in a few months would identify whether there is any apparent motion, and the parallax would give a distance. Even at the speed of light matter can't move so far as to suddenly be in the frame in just 2.5 months, even within our own galaxy, never mind the range of M31, so it can't be distant.