Explosive Molecular Outflows

Abstract

About fifteen years ago a new type of extreme (with kinetic energies of $\mathrm{E}_k \sim 10^{47-49}\, \mathrm{erg}$) molecular outflows associated with very luminous ($\geq 10^5\, \mathrm{L}_\odot$) and massive (10$^3$ M$_\odot$) young clusters was confirmed, the Explosive Molecular Outflows. This new class of outflows is largely different from the classical bipolar protostellar flows, with spatial distributions made of numerous narrow straight filament- or streamer-like ejections in an almost isotropic arrangement and with clear Hubble--Lemaître-like expansion motions. Straight filaments point directly to the center of expanding molecular or ionized shells, which exhibit expansion velocities of about 10--50 km s$^{-1}$. However, no young massive stars are clearly located there, probably because they moved to other places. These physical characteristics suggest that explosive outflows are short-lived in nature and possibly generated by an energetic single and brief disrupting event. The most up-to-date theoretical model for explaining their nature involves the disruption of non-hierarchical massive protostellar systems, where members may either form a close binary (with separations of a few au) or merge into a single massive star, as recently proposed for the nearest high-mass star-forming region, Orion BN/KL.