"Binary" appears to be Nature's preferred mode for forming stars.

  • More than 50% of all stars exist in small multiple systems with equal numbers in equal logarithmic intervals of the period. [Abt 1983]

  • There appear to be very different secondary-mass distributions for binaries with periods less than or greater than 100 years. [Abt 1983]

  • The frequency of binaries in star forming regions appears to be very similar to the frequency on the main sequence. [Mathieu et al. 1994]

Although many many numerical simulations have been performed over the past two decades in an effort to show to what extent a "Jeans-type" fragmentation occurs during the collapse of a rotating, protostellar gas cloud, two major problems exist regarding our understanding of how binary stars form [Bodenheimer 1995; see also Shu et al. 1987]:

  • Simulations show that "the most likely initial condition in the core of a molecular cloud [i.e., a centrally condensed configuration] appears to be stable against fragmentation."

  • "... the theoretical difficulty in forming close binaries; almost all the current simulations produce relatively wide binaries."

Proposed Solutions:

  • Capture.

  • Orbital Decay.

  • Disk fragmentation.

  • Fission.

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