 With a mass only 80 times that of Jupiter ( MJ ) , <unk> <unk> @-@ <unk> is the smallest known star undergoing nuclear fusion in its core . For stars with metallicity similar to the Sun , the theoretical minimum mass the star can have and still undergo fusion at the core , is estimated to be about 75 MJ . When the metallicity is very low , however , the minimum star size seems to be about 8 @.@ 3 % of the solar mass , or about 87 MJ . Smaller bodies called brown dwarfs , occupy a poorly defined grey area between stars and gas giants . 
