A star explodes every second or so, somewhere in the universe. It's how they die, and astronomers call the events supernovas. While much has been learned over the past few decades, supernovas remain somewhat elusive. Among the trickiest aspects of studying them is to spot a star exploding and figure out what kind of star it was before it fired.
http://www.space.com/scienceastronomy/050801_hubble_supernova.html
http://www.space.com/scienceastronomy/050801_hubble_supernova.html