Molecular Hydrogen Microstructures in Planetary Nebulae

Abstract

Molecular hydrogen (H 2 ) emission is commonly detected in planetary nebulae (PNe), specially in objects with bipolar morphologies. New studies showed that H 2 gas is also packed in microstructures embedded in PNe of any morphological type. Despite the presence of H 2 in cometary knots being known for years, only in the last five years, much deeper imagery of PNe have revealed that H 2 also exists in other types of low-ionisation microstructures (LISs). Significant differences are found between the host PNe of cometary knots and other types of LISs, such as nebula age, central star temperature (evolutionary stage) and the absolute sizes of the microstructure itself.