The Andromeda galaxy is now estimated to be more than 220,00 light-years across, triple the previous estimate of 70,000 to 80,000 light-year.
An old picture of the Andromeda galaxy
A group of scientists studied the motions of about 3,000 stars and discovered they are not a halo but a part of the galaxy's disk. They found out that that the stars are sited in the plane of the Andromeda disk itself and move at a velocity which suggests they are in orbit around the center of the Andromeda galaxy. More info at Reuters