An image provided by NASA on Thursday shows the Cartwheel galaxy. About 100 million years ago, a smaller galaxy plunged through the heart of Cartwheel, creating ripples of star formation. (Associated Press/NASA)
The Cartwheel galaxy
An image provided by NASA on Thursday shows the Cartwheel galaxy. About 100 million years ago, a smaller galaxy plunged through the heart of Cartwheel, creating ripples of star formation. (Associated Press/NASA)