When the spaceship entered superluminal travel, the celestial system fleet instantly disappeared into a deep darkness. The light emitted from there couldn't catch up with our spaceship, creating the illusion that the mother fleet had vanished.
Of course, this was just what appeared at the optical layer. The warship's information-gathering observation device still displayed the celestial system fleet, now reduced to a small dot. The bright Ghost Energy Death Star emitted a shining blue light in the darkness, and the explosions and gunfire in the sky above the fleet had turned into a fuzzy glow. Seconds later, the celestial system fleet became a pixel on the screen before disappearing from view.
