Explanation: This galaxy is having a bad millennium. In fact, the past 100 million years haven't been so good, and probably the next billion or so will be quite tumultuous. Visible on the upper left, NGC 4038 used to be a normal spiral galaxy, minding its own business, until NGC 4039, toward its right, crashed into it. The evolving wreckage, known famously as the Antennae, is pictured above. As gravity restructures each galaxy, clouds of gas slam into each other, bright blue knots of stars form, massive stars form and explode, and brown filaments of dust are strewn about. Eventually...