There is a general consensus that the frequencies of the kilohertz Quasi-Periodic Oscillations ( kHz QPOs ) in neutron-star low-mass X-ray binaries are directly linked to the spin of the neutron star .
The root of this idea is the apparent clustering of the ratio of the frequency difference of the kHz QPOs and the neutron-star spin frequency , \Delta \nu / \nu _ { s } , at around 0.5 and 1 in ten systems for which these two quantities have been measured .
Here we reexamine all available data of sources for which there exist measurements of two simultaneous kHz QPOs and spin frequencies , and we advance the possibility that \Delta \nu and \nu _ { s } are not related to each other .
We discuss ways in which this possibility could be tested with current and future observations .