As I understand the law of inertia, an object in motion tends to stay in motion, particularly in outerspace. And when one considers the extraordinary force and speed with which a Supernovae explodes, surely all of that plasma and matter should be flying away at incredible speeds for infinity. So, how then, in nebula where Supernovae occur, does any of the matter that exploded out remain in it? Shouldn't it just force its way out at incredible speeds, forever? As the materials that are jettisoned are essential in creating solar systems, because of their heavier elements, I'm just uncertain how these powerfully accelerated particles could be made to conveniently stick around, when they need to. Does anyone know how that works?