The Milky Way is our home. An island of stars in a universe of other galaxies. But you might be surprised to learn that astronomers have only known the Milky Way’s true nature for just a century. Let’s learn the history of discoveries about the Milky Way, and what today’s science tells us. And let’s peer into the future to learn the ultimate fate of our galaxy.

Last week we talked about galaxies in general, and hinted at the most violent and energetic ones out there: active galaxies. Quasars have been a mystery for half a century; what kind of object could throw out more radiation than an entire galaxy? A black hole, it turns out, with the mass of hundreds of millions of suns performs this feat. Let’s trace back the history of quasars, how they were first discovered and puzzled astronomers for so long. And let’s look at what we know today.