http://www.newsweek.com/gargantuan-collision-giant-galaxy-gaia-enceladus-filled-milky-way-stars-1195955

Imagine trying to map out your home town using only information you could gather from your window. Even with a pair of binoculars you’d find it a difficult task. Mapping out our own galaxy, the Milky Way, is a similarly daunting mission. Unlike other galaxies that we can view from a distance, we sit inside the Milky Way—around 26,000 light years from its centre. This means that when we try to look at the opposite side of the galaxy, much of our view is blocked by the stars and dust in between.

But on April 25, our view of the Milky Way became much clearer. The European Space Agency’s Gaia satellite provided us with positions, distances and motions of 1.3 billion stars measured to a higher precision than ever before. Now this same data has helped researchers work out how our galaxy filled up with a considerable amount of its stars. The results have just been published in Nature.