HD 5980 (RMC14) is a multiple system of massive stars in the Small Magellanic Cloud, located at a distance of about 210,000 light-years (70 kiloparsecs). It is the brightest member of the giant HII region N66 which includes the association OB NGC 346. HD 5980 has many features that make it a very particular star. It is the main source of ionization of the HII N66 region, contributing with 25% of the ionizing photons (N66 is the most important HII region of the Small Magellanic Cloud). HD 5980 is made up of at least three stars: the pair A + B is an eclipsing binary system with an orbital period of 19.3 days, while the star C (not resolved in Hubble Space Telescope images) is apparently gravitationally linked to system A + B, and also appears to be a member of a binary system with a 96-day orbital period. That is, HD 5980 could be a quadruple star system composed of two massive binaries orbiting with a common center. Components A and B show characteristics of Wolf-Rayet stars, and mutually eclipse. The stellar component A has been shown to be a fascinating star undergoing remarkable spectral and bright transformations during the last decades, being its culminating moment a variable eruption of luminous blue type between 1993 and 1994. HD 5980 was the first extragalactic binary system where it was detected collision of stellar winds on X-rays.
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