private function appendSystem(GalaxyEntity $galaxyEntity)
{
$systemEntity = new SystemEntity();
$systemEntity->setGalaxy($galaxyEntity);
$systemEntity->setNumber($galaxyEntity->countSystems());
$this->em->persist($systemEntity);
$celestialBodyCount = rand($this->universeEntity->getMinCelestialBodies(), $this->universeEntity->getMaxCelestialBodies() - 1);
for ($i = 0; $i < $celestialBodyCount; ++$i) {
$this->appendCelestialBody($systemEntity);
}
}
