Nova

The Nova is a Hardmode enemy which spawns on the Surface Astral Infection biome. Initially, it loosely hovers near the player. If it maintains a line of sight on the player for long enough, it starts pulsating and stops in place, then begins to accelerate in a straight line until it collides with the player or any surface, exploding on contact.

Trivia

 * This enemy is named after a nova (Latin for "new", as in "new star"); a strong and rapid increase in the brightness of a star.