Galactic feedback
= Galactic feedback
<galactic feedback> couples <star formation> or <black-hole accretion> to the surrounding <gas> through <energy>, <momentum> and <mass> exchange. It includes <stellar feedback> and <active-galactic-nucleus feedback>. A feedback loop may heat, stir, expel or compress <gas>, so its sign depends on how the <gas> supply and cooling respond; <energy> injection alone does not establish a lasting reduction of <star formation>.