Emission from vibrationally excited molecular hydrogen has been discovered in a variety of objects of widely differing ages and environs including molecular clouds, planetary nebulae, and a Seyfert galaxy. The observations of the H2 spectra indicate this emission arises in hot, nearly thermalized gas. While there is still some disagreement between detailed predictions of hydrodynamic calculations and recent observations, it is generally believed that energy supplied to the interstellar gas in the form of shock waves is responsible for the observed H2 emission.
Several of the H2 sources are molecular clouds associated with ongoing star formation, most notably the Orion Molecular Cloud. From the intensity, strength, temperature, and velocity of the molecular hydrogen emission, it is estimated that at least 1048 ergs has been deposited in the cloud over the last thousand years or so in the form of bulk kinetic energy. There is no clear explanation for this process, since the energy is large and the timescale short, and it appears unlikely that we should observe such events unless they occur frequently. Among the other H2 sources in molecular clouds, NGC 7538, DR 21, and W3 are of similar spatial extent and apparent luminosity as the Orion emission.