Our Corrugated Galaxy
Dr. Newberg and her group were studying stars above and below the galactic plane that were thought to be not part of our galaxy, but tidal "trails" from dwarf galaxies that had been torn apart by the massive gravity of the Milky Way. But they realized that the pattern of distances to these stars told a different story - that the outer part of the disk of our galaxy had large ripples in it, with stars pushed up and down like waves from a pebble dropped in a pond. Including these stars in our galaxy makes the disk about 50% larger.
Dr. Newberg suspects this disturbance in the disk of the galaxy is from a dwarf galaxy passing through the plane of the Milky Way, and that event may be responsible for creating the swirling spiral arms as well.