The rapidly changing period of the QPE source 1ES 1927+654

ABSTRACT Several low-mass galaxy nuclei are observed to produce quasi-periodic eruptions (QPEs). Recently one of these systems, 1ES 1927+654, changed its quasi-period drastically, from ∼18 to ∼7.1 min, over a span of just 2 yr. I suggest that this is an effect of von Zeipel–Lidov–Kozai (ZLK) cycles, where a more distant star orbits the QPE ‘binary’ in which a white dwarf orbits a moderately massive central black hole. I show that in 1ES 1927+654 the white dwarf’s orbital plane oscillates with angular amplitude $\simeq 71^{\circ }$ each side of the orbital plane of the distant star. This causes correlated changes of the orbital eccentricity and quasi-period, and of the accretion luminosity driven by gravitational radiation losses. The gravitational radiation (GR) luminosity has the characteristic property that it is inversely proportional to the instantaneous binary quasi-period in all cases. The QPE system is probably just one of the effects produced by a complex infall event involving several stars. The whole system is likely to evolve rapidly, and will repay further monitoring.