The extended stellar disk has gone undetected in the past because the stars that appear in the region of the disk could not be known to be a part of the disk until their motions were calculated. In addition, the inhomogenous "fuzz" that makes up the extended disk does not look like a disk - it appears to be a fragmented, messy halo built up from many previous galaxies crashing into Andromeda, and it was assumed that stars in this region would be going every which way. Credit: Scott Chapman, Caltech
