Formation of wide binary stars from adjacent cores
  Wide gravitationally bound pairs of stars can be formed from adjacent
prestellar cores that happen to move slowly enough relative to each other.
These binaries are remnants of the primordial clustering. It is shown that the
expected fraction of wide bound pairs in low-density star formation regions can
be larger than the fraction of wide pairs in the field. On the other hand, wide
binaries do not form or survive in dense clusters. Recent works on the
separation distribution of young binaries, summarized here, confirm these
expectations. Alternative formation mechanisms of wide binaries such as cluster
dissolution or unfolding of triple stars cannot explain the large observed
fraction of young wide pairs and therefore are not dominant. The fact that more
than a half of wide pairs contain subsystems matches the general multiplicity
statistics and does not imply that hierarchical multiplicity and wide binaries
are genetically related.
