A Super-Jupiter Driving Orbital Decay of WASP-4b

The orbital change of the Hot Jupiter WASP-4b constitutes a difficult enigma for the theory of exoplanetary dynamics which are normally explained by tidal interactions with the host star; but here we consider an alternative explanation attributing the perturbation to the gravitational influence from an unseen third body. To test this hypothesis, a model was built and analyzed on the basis of the entire set of mass ephemerides with new modeling possibilities from the radial velocity (RV) datasets compiled by HARPS over several years. CORALIE and HIRES measurements together with a combination of Hubble Space Telescope observations and archival Kepler Transit Timing Variations results enable us to infer the existence of a hitherto unknown massive companion, having a 6.5 MJup mass, on a ~7.58 au orbit around WASP-4A, a B8V star slightly more luminous than the Sun. We establish a connection between such a massive companion and the observed orbital decay of WASP-4b; it is revealed through CORALIE and HIRES time-series that massive companions gravitationally perturb such systems, altering the expected period and causing apparent changes in their orbital timing, without tidal effects being involved.