Musca (abbreviation Mus, genitive Muscae) is one of the minor southern (
declination -70 degrees)
constellations. It contains the
soft X-ray transient Nova Muscae 1991. Nova Muscae 1991 which is a
binary star where one of the stars is a
black hole. During the 1991 outburst,
radiation produced by
positron annihilation[?] was detected from Nova Muscae.