This ejected gas is GLOWING at all wavelengths, from
radio waves all the way through gamma rays. This is an X-ray picture
of the million degree temperature gas that has been ejected from
a supernova explosion that occurred more than a thousand years
ago.
These supernova remnants can last for thousands of
years, expanding with time, getting fainter and fainter, until
they finally disperse and blend in with the general interstellar
gas.
