A unique QPO often occurs at 6 Hz in Z type Neutron star sources radiating close to the Eddington limit. From radio observations, it is known that a jet is present during the 6 Hz QPO and sometimes ultra relativistic flow is also associated. In general these sources the QPO varies from ~20-50 Hz during which the inner region of accretion disk is truncated and a Compton cloud/corona is present inside the truncation radius. As the truncated front approaches close to the last stable orbit (50 Hz), suddenly a unique 6 Hz QPO appears. I will discuss a model which probably explains the sudden emergence of the 6 Hz QPO along with 50 Hz QPO. In this model, I study the disk oscillation during which the inner region of the disk dominated by radiation pressure assuming that the oscillation is driven by the gravitational force. I will also use this model explain the sudden occurrence of type-B/A QPOs in black hole X-ray binaries which are similar to the 6 Hz QPO in neutron star source.