A dragon and a tadpole slither low across the northern sky this evening, curling around the North Star. The dragon is the long but faint constellation Draco. And the tadpole is the aftermath of a galactic collision that’s just below the dragon’s long, winding body. The Tadpole galaxy is about 400 million light-years away. An image from Hubble Space Telescope shows a bright “head” with a long, wiggly “tail” extending away from it. The head is the body of the galaxy itself — a spiral that’s perhaps a little bigger than our home galaxy, the Milky Way. The tail is a streamer of stars and gas that stretches across a quarter-of-a-million light-years. It was pulled out of the galaxy’s disk by a collision with a smaller galaxy at least a hundred million years ago. That collision squeezed vast clouds of gas in the disk and in the tail, causing them to collapse and give birth to new stars. Astronomers have discovered dozens of young star clusters, including a few that have hundreds of thousands
