Estimates vary. A lot. Space.com reports that the range accepted by many astronomers is 100-200 billion (bit.ly/galaxies-billions). As if that weren’t a pretty wide range already, phys.org reports that a group of European researchers recently found that we’d missed a few, and the number could be more like 2 trillion. (bit.ly/galaxies-trillions). Incidentally, the team that found 2 trillion was begun by an undergraduate student (Aaron Wilkinson) who is now close to done with his Ph.D. on this very topic.