Milky Way arms pinned down

I find this fascinating and if nothing else it serves to show what we "know" is in a continual state of modification. Another "woah!" moment based upon a new discovery-

Astronomers have made the most detailed map ever of our galaxy's overall shape, showing that its spiral arms extend much further than expected....

The map shows that our galaxy's spiral structure is not symmetrical around its centre but contains more arms in some areas than others. Contrary to theoretical predictions, the arms also continue well beyond the distance at which stars should be found...

Scientists believe that the spiral structure is driven by the gravity of the disk. "But we are seeing spiral structure even where gravity seems to be too weak to drive it. Why? How?" asks Blitz.

>LINK<