from strong emission lines of  hydrogen molecules and singly ionized nitrogen. The green areas, on the other hand, are primarily oxygen in different states of ionization and excitation. Scientists have concluded that material from the red filaments was in the outer layers of the star prior to its explosion as a supernova, while that from the green filaments was deep inside the star. By studying this material, astronomers can learn what was inside the star itself, much as a bomb expert determines the design of a bomb from the physical evidence left after its explosion.