Scientists have known about the nebula 30 Doradus for some time. It's 25 million years old, it makes stars, and it might be running out of fuel. 

But they only recently discovered that what seemed to be one star-forming region is, in fact, two. This picture, captured by the Hubble three years ago, shows the two regions, one a million years older than the other, in their slow collision.

Below, recent Pictures of the Day: