The vibrating galaxy

At http://arxiv.org/abs/1302.2468 and http://tallbloke.wordpress.com/2013.10/23/milky-way-turns-out-to-be-a-vo… and even http://phys.org/print301684171.html … the wobbling galaxy with velocities going upwards and downwards, seems to show our galaxy has a wave like motion, with stars on the edge sloshing in and out. Being a spiral galaxy it rotates around the galactic centre – now it can also be seen to wobble, somewhat akin to aurora, or a flag waving in the breeze. Why this is happening is not known – or the source of the force making it do so.