Meaning: This sentence is describing how supernovas explode. It's like they are saying goodbye with a fiery and powerful explosion.
Choice of Words: "Supernovas" are the powerful explosions of massive stars at the end of their lives. "Exploded" is a verb that describes the sudden and violent release of energy. "Fiery farewells" suggests that the supernovas are saying goodbye with a spectacular display of light and energy.