  We study the formation of a giant gas planet by the core--accretion
gas--capture process, with numerical simulations, under the assumption that the
planetary core forms in the center of an anti-cyclonic vortex. The presence of
the vortex concentrates particles of centimeter to meter size from the
surrounding disk, and speeds up the core formation process. Assuming that a
planet of Jupiter mass is forming at 5 AU from the star, the vortex enhancement
results in considerably shorter formation times than are found in standard
core--accretion gas--capture simulations. Also, formation of a gas giant is
possible in a disk with mass comparable to that of the minimum mass solar
nebula.
