Description
Quasi-periodic oscillations (QPOs) are a common feature observed in accreting compact objects, including black holes, neutron stars, and, as recently discovered, accreting white dwarfs (AWDs). In X-ray binaries (XRBs), these QPOs are often attributed to mechanisms such as relativistic frame-dragging (Lense-Thirring precession, but their true origin remains debated. Here, I will present recent work that has identified new optical QPOs in five AWDs with characteristic frequencies and harmonic structures analogous to those seen in XRBs. Since Lense-Thirring precession is excluded in the non-relativistic regime of AWDs, these QPOs must arise from a different mechanism. I will discuss the proposed model of these QPOs which are caused by magnetically driven disc warping and precession. I will further discuss the extension of this framework to pulsating ultraluminous X-ray sources (PULXs), a class of extreme XRBs exhibiting super-Eddington accretion rates hosting a neutron star. By modelling magnetically-driven precession, we can reproduce the observed spin and QPO frequencies of pulsating ULXs, obtaining realistic order of magnitude estimates for magnetic field strengths and accretion rates. This unified interpretation suggests that accretion flows around compact objects, regardless of scale, can exhibit similar behaviour under magnetic influences, providing a candidate explanation for mHz QPOs in a wide variety of astrophysical systems. Further observations of AWDs and PULXs will test this model, potentially offering new insights into our understanding of QPOs in accreting compact objects.
