into forming a disc around the protostar. However, if it has less specific angular momentum initially, there is no excess angular momentum to form a circumstellar disc, and it must gain angular momentum even to be captured by the protostar. In this case, the infalling gas gains angular momentum as it falls on to the protostar in a Bondi-Hoyle-type accretion stream. In practice, this means that a circumstellar disc is almost always formed around the primary, but the secondary does not have a circumstellar disc unless the infalling gas has more specific angular momentum that some critical value. In a similar way, the formation of a circumbinary disc only begins when the specific angular momentum of the infalling gas is great enough for the gas to form a circular orbit at a radius greater than that of the secondary from the centre of mass of the binary.

Development of a Protobinary Evolution Code
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Using the quantitative results of Bate & Bonnell [@BatBon97], Bate [@Bate2000] developed a protobinary evolution (PBE) code which follows the evolution of a protobinary system as it accretes from its initial to its final mass, but does so in far less time than would be required 