What is the history of the interstellar medium?
As you may have learned by now, the interstellar medium contains particles that have origins in many different events. The majority of the interstellar gas and dust that we see was produced by star death. We do not ordinarily think of stars as transient objects — after all, the constellations do not change perceptibly in our lifetimes, and stellar events on a scale that we can see are rather rare — but even stars are born, and must also eventually die. Stars produce energy by the process of fusion — two or more atoms, like hydrogen or helium, are combined under intense pressure and temperature to produce a heavier atom. This releases a fantastic amount of energy, which then allows the reaction to continue elsewhere in the star. (Humanity has harnessed this process to a degree in its nuclear weapons: the bombs that were used in World War II were fission bombs, which split atoms, and although they produce much energy — hense much devastation — this energy pales in comparison to the
