Hercules X-1 - A neutron star with a twisted accretion disk

A model is proposed for the binary X-ray source Her X-1, in order to explain its 35-day periodicity. It consists of a normal star and a neutron star with a twisted accretion disk. The 35-day clock in the model is provided by a precession of the normal star. The disk is responsible for a periodic obscuration of the pulsed X-rays, causing the on-off behavior. The twisted shape of the disk, which arises naturally from the precession of the normal star, is shown to explain a considerable number of X-ray and optical observations. (AIP)