High-frequency quasiperiodic oscillations of the X-ray flux comming from black-hole binaries have the potential to provide precise estimates of the mass and the spin of the central black hole, if an adequate model for them was available. There are several models in the literature but none of them is commonly accepted. One way to test the available models is to confront their predictions for the masses of black holes with results obtained through other methods. Here, we study the mass bounds that nine of the most commonly used models provide for the three microquasars with known masses GRS 1915+105, GRO 1655-40 and XTE 1550-564 which display high-frequency quasiperiodic oscillations in their X-ray spectra. We also propose a statistical method for the assessment of the average success of the models. The results allow us to discard five of them. Here, "the mass problem" designates the conflict between their predictions and the reference masses.

The high frequency quasiperiodic oscillations (QPOs) in the X-ray spectra of the millisecond pulsar XTE J1807-294 are under consideration. By application of the relativistic precession (RP) model an attempt is made to approximate the observed frequencies as well as to assess the mass and the angular momentum of the object. The obtained mass is too high for a neutron star.

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