What impact does a hypernova explosion, or a GRB, have on its environment?
The blast wave from a hypernova explosion can sweep up its surrounding interstellar gas to form a dense shell, that may enclose a tenuous, very hot (million degree) plasma. Such a remnant can last tens of million years. But similar remnants may also be produced by other mechanisms, such as multiple supernova explosions. Thus it is normally difficult to be sure about the true origin of such remnants, except for relatively young ones such as the two discovered in M101.
