Processes creating pulsar wind nebulae are complicated .
Processes evolve through various phases before creating a so - called relic nebula , which is visible as a wind bubble , shell nebula , or as a bow - shock .
Processes creating pulsar wind nebulae are complicated and they evolve through various phases before creating a so - called relic nebula , which is visible as a wind bubble , shell nebula , or as a bow - shock .