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The problem of disk accretion onto the surface of a neutron star with a weakmagnetic field at a luminosity exceeding several percent of Eddington isreduced to the problem of the braking of a hypersonic flow with a velocity thatis 0.4-0.5 of the speed of light above the base of the spreading layer -- adense atmosphere made up of previously fallen matter. We show that turbulentbraking in the Prandtl-Karman model with universally accepted coefficients forterrestrial conditions and laboratory experiments and a ladder of interactinggravity waves in a stratified quasi-exponential atmosphere at standardRichardson numbers lead to a spin-up of the massive zone that extends to theocean made up of a plasma with degenerate electrons. Turbulent braking in theocean at the boundary with the outer solid crust reduces the rotation velocityto the solid-body rotation velocity of the star. This situation should lead tostrong heating of deep atmospheric layers and to the switch-off of theexplosive helium burning mechanism. Obviously, a more efficient mechanism forthe dissipation of a fast azimuthal flow in the atmosphere should operate inX-ray bursters. We show that a giant solitary gravity wave in the atmospherecan lead to energy dissipation and to a sharp decrease in azimuthal velocity infairly rarefied atmospheric layers above the zone of explosive helium burningnuclear reactions. We discuss the reasons why this wave, that has no directanalog in the Earth's atmosphere or ocean, appears and its stability. We posethe question as to whether neutron stars with massive atmospheres, spun up tohigh velocities by accreting matter from a disk, can exist among the observedGalactic X-ray sources.

Spread of Matter over a Neutron-Star Surface During Disk Accretion: Deceleration of Rapid Rotation