  It is generally thought that conservative mass transfer in Algol binaries
causes their orbits to be wider, in which the less massive star overflows its
Roche-lobe. The observed decrease in the orbital periods of some Algol binaries
suggests orbital angular momentum loss during the binary evolution, and the
magnetic braking mechanism is often invoked to explain the observed orbital
shrinkage. Here we suggest an alternative explanation, assuming that a small
fraction of the transferred mass forms a circumbinary disk, which extracts
orbital angular momentum from the binary through tidal torques. We also perform
numerical calculations of the evolution of Algol binaries with typical initial
masses and orbital periods. The results indicate that, for reasonable input
parameters, the circumbinary disk can significantly influence the orbital
evolution, and cause the orbit to shrink on a sufficiently long timescale.
Rapid mass transfer in Algol binaries with low mass ratios can also be
accounted for in this scenario.
