Dicke’s Superradiance in Astrophysics
Abstract
It is generally assumed that in the interstellar medium much of the emission emanating from atomic and molecular transitions within a radiating gas happen independently for each atom or molecule, but as was pointed out by R. H. Dicke in a seminal paper several decades ago this assumption does not apply in all conditions. As will be discussed in this thesis, and following Dicke’s original analysis, closely packed atoms/molecules can interact with their common electromagnetic field and radiate coherently through an effect he named superradiance. Superradiance is a cooperative quantum mechanical phenomenon characterized by high intensity, spatially compact, burst-like features taking place over a wide range of time-scales, depending on the size and physical conditions present in the regions harbouring such sources of radiation. I will discuss the potential for superradiance in the atomic hydrogen 21-cm line for which we extended Dicke’s analysis to the magnetic dipole interaction characterizing this line. Then, the application of superradiance to the OH 1612-MHz, CH3OH 6.7-GHz and H2O 22-GHz maser lines will be discussed, and it will be shown that super-radiance provides a valid explanation for previous observations of intensity flares detected in these spectral lines for some astronomical sources. An interesting result is that superradiance provides a natural mechanism for the recent observations of periodic and seemingly “alternating” methanol and water flares in G107.298+5.639 that cannot be easily explained within the context of maser theory.