Detection of a Noble Gas Molecular Ion, ³⁶ ArH ⁺ , in the Crab Nebula

TLDR

Noble gas molecules have not yet been detected in space, and {36}Ar is thought to originate from explosive nucleosynthesis in massive stars during core‑collapse supernovae. The likely excitation mechanism for the observed {36}ArH⁺ emission lines is electron collisions in partially ionized regions with electron densities of a few hundred per cubic centimeter. Spectra from the Herschel Space Observatory reveal 617.5 GHz and 1234.6 GHz emission from {36}ArH⁺ in the Crab Nebula, confirming that noble gas molecules can form in supernova remnants.

Abstract

Noble gas molecules have not hitherto been detected in space. From spectra obtained with the Herschel Space Observatory, we report the detection of emission in the 617.5 GHz and 1234.6 GHz J = 1-0 and 2-1 rotational lines of {36}ArH^+ at several positions in the Crab Nebula, a supernova remnant known to contain both H2 molecules and regions of enhanced ionized argon emission. {36}Ar is believed to have originated from explosive nucleosynthesis in massive stars during core-collapse supernova events. Its detection in the Crab Nebula, the product of such a supernova event, confirms this expectation. The likely excitation mechanism for the observed {36}ArH^+ emission lines is electron collisions in partially ionized regions with electron densities of a few hundred per centimeter cubed.