Syncronizing novas could be fun. Make the stars in a galaxy go nova in nice patterns.
Black holes can be fun to play with.
Take two and let them revolve around each other. Try to make them collide in topologically interesting patterns. They used blue-white supergigants for the headline, and more modest stars for the rest of the text. Make a sun flare up, and place a silloutte in front of nearby planets. The result is that your message will be written on the surface.