The most distant object easily visible to the human eye is the Andromeda Galaxy, roughly two million light-years away, our nearest neighbor galaxy, and very very large. Without a telescope Andromeda looks like a faint, gassy cloud in the constellation Andromeda. Conventional astronomical reasoning for years has held that Andromeda, also known as M31, was larger and denser than our own Milky Way galaxy. Using a high-end telescope, and multiple digital images, Andromeda looks like the image embedded to the left.
Thanks to research presented this week at the American Astronomical Society's annual convention, we now know we're in a galactic neighborhood every bit as good as Andromeda. Using the Very Long Baseline Array, scientists have managed a much more detailed three-dimensional map of the Milky Way, and discovered it's 15% larger in breadth, much denser than we thought, with 50% more mass (and more stars!). The Milky Way is also shaped differently than previously thought. It appears to have four, not two, spiral arms of gas and dust, giant clouds of gas where new stars are forming, as you can see in this artist’s rendition above (we haven't as yet the ability to take pictures of the Milky Way from outside, since, well, we're in it, about is about 28,000 light-years from the center, on one of the arms). Do click the image to read the annotations on the linked page.
That's the good news.
The bad news is that additional mass means much greater gravity, which means, well, the Milky Way sucks more, increasing the likelihood that our galaxy will collide with Andromeda, or even smaller but still nearby galaxies.