The detection of the radical species S₂H was reported in 2017 by Fuente et al. toward the Horsehead nebula, one of the best known and most imaged deep space objects. The observations were made with the IRAM 30m telescope (one of the most prolific tools for detecting new astromolecules). A total of 8 lines were assigned to S₂H.

S₂H, also given as HS₂ or HSS, is the radical of H₂S₂ or (di)hydrogen disulfide, also known as hydrogen persulfide. While H₂S₂ has not been detected to date, the oxygen analogs have both been observed: the detections of hydrogen peroxide (H₂O₂) and the hydroperoxyl radical (HO₂) were reported in 2011 and 2012, respectively. In the absence of a common name, "hydropersulfide radical" might be an appropriate label for HS₂, to be consistent with HO₂.