Quasi-periodic oscillation
= Quasi-periodic oscillation
{title2=QPO}
An oscillatory feature with finite width in a source's variability <power spectrum>, rather than a perfectly periodic clock. Orbital, precession and disc-mode interpretations connect different <frequencies> to the same compact object. Identifying an observed peak with an <innermost stable circular orbit> orbital <frequency> is therefore a model assumption, not a direct black-hole <mass> or spin measurement.