Swallowed Planets Spin up Stars, Explaining Rapid Rotation in Distant Systems

Scientists investigate how the dissipation of internal gravity waves within stars influences the evolution of star-planet systems. Yaroslav A. Lazovik from Sternberg Astronomical Institute, Lomonosov Moscow State University, and Adrian J. Barker from School of Mathematics, University of Leeds, alongside their colleagues, demonstrate that tidal interactions and subsequent gravity wave damping can explain the enhanced stellar rotation observed in systems such as TOI-2458 and GJ 504. This research is significant because it identifies a mechanism by which stars may engulf their hot Jupiter planets, and successfully categorises observed hot Jupiters into populations defined by the stage of gravity wave dissipation. Their population synthesis modelling suggests up to 20% of stars within a specific mass range may have already engulfed a former hot Jupiter, revealing a crucial process shaping the architectures of these planetary systems.

Stellar Consumption of Hot Jupiters Explains Enhanced Rotation Rates in young stars

Scientists have uncovered a previously unconfirmed pathway for how stars and planets interact, revealing that stars can effectively “consume” planets. This work centres on the enhanced stellar rotation observed in stars TOI-2458 and GJ 504, demonstrating that this phenomenon can be explained by the prior engulfment of a hot Jupiter planet.
The dissipation of internal gravity waves within the star drives this process, offering new insights into planetary system evolution and the ultimate fate of hot Jupiters. Researchers applied tidal prescriptions modelling wave breaking in stars with radiative cores and magnetic wave conversion in stars with convective cores to arrive at this conclusion.

By modelling these processes, they successfully explained the observed stellar rotation rates, indicating a prior interaction with a hot Jupiter. Furthermore, the observed population of hot Jupiters has been divided into two distinct groups: those too young for significant gravity wave dissipation and those where the process is currently ongoing.

These two groups exhibit markedly different orbital period distributions. Younger systems display a uniform distribution, while older systems show a steep decline at shorter periods, a pattern successfully reproduced through population synthesis modelling. The study estimates that up to 20% of main-sequence stars with masses between 0.7 and 1.5 solar masses may have engulfed a hot Jupiter planet during their lifetimes. This finding highlights the crucial role of internal gravity wave dissipation in shaping the architectures of hot Jupiter systems and provides a new understanding of planetary system dynamics.

Calculating tidal quality factors and modelling dissipation mechanisms are crucial for understanding estuarine hydrodynamics

Tidal prescriptions modelling internal gravity wave dissipation form the basis of this study’s methodology. The stellar modified tidal quality factor, Q′, is a fundamental quantity calculated to model tidal dissipation, defined proportionally to the ratio of maximum potential energy stored in the tide to the energy dissipated over one tidal period.

This calculation utilizes the second-order potential Love number, k2, assumed to be 0.0351 for the Sun, and considers circular planetary orbits in the equatorial plane of a star. The orbital frequency, n, is determined using the gravitational constant, planetary mass, stellar mass, and orbital semi-major axis, while the tidal frequency, ωtide, depends on stellar rotation frequency and orbital frequency.

Researchers focused on two primary dissipation mechanisms for tidally excited internal gravity waves: wave breaking in stars with radiative cores and magnetic wave conversion in stars with convective cores. These processes are considered the most efficient means of dissipating internal gravity waves unless resonant excitation of a global g-mode oscillation occurs, a scenario potentially limited by nonlinear effects and internal stellar rotation evolution.

The corresponding tidal quality factor, Q′, characterizing efficient tidal dissipation in a “fully damped regime”, is expressed as an equation incorporating parameters such as the stellar radius, mass, gravitational constant, and tidal frequency. The parameter Γ, used in the calculation of Q′, is determined following a previously published equation, allowing for consistent application of the model.

While the equation theoretically applies to fully damped waves regardless of the specific mechanism, it is applied specifically when waves exhibit strong nonlinearity leading to breaking or undergo linear magnetic wave conversion. Additional linear and weakly nonlinear processes, such as radiative damping or secondary wave excitation, are not explicitly considered to maintain focus on the primary dissipation mechanisms. To isolate the effects of internal gravity wave dissipation, age restrictions are imposed, excluding young systems potentially influenced by efficient inertial wave dissipation, and equilibrium tides are neglected due to expected ineffectiveness in the studied stars.

Stellar Rotation Enhancement via Hot Jupiter Engulfment and Gravity Wave Dissipation represents a plausible angular momentum transfer mechanism

Scientists demonstrate that the enhanced stellar rotation observed in stars TOI-2458 and GJ 504 is attributable to the prior engulfment of a hot Jupiter planet, a process facilitated by the dissipation of internal gravity waves within the star. This research reveals a previously unconfirmed pathway for planet-star interactions, fundamentally altering our understanding of planetary system evolution and the ultimate fate of hot Jupiters.

Population synthesis modelling successfully reproduces the main features of older hot Jupiter samples based on the distribution of younger systems, supporting this engulfment hypothesis. Detailed analysis indicates that up to 20% of main-sequence stars with masses between 0.7 and 1.5 solar masses may have engulfed a hot Jupiter planet during their lifetimes.

This substantial fraction highlights the prevalence of this previously unrecognised stellar consumption process. Observed orbital period distributions differentiate young hot Jupiter systems, which exhibit a uniform distribution, from older systems, displaying a steep decline at short periods. The study connects these differing distributions to the dissipation of internal gravity waves, with younger systems still undergoing this process and older systems reflecting the aftermath of planetary engulfment.

Stellar rotation rates in TOI-2458 and GJ 504 were specifically examined, and the observed enhancements align with predictions based on the dissipation of internal gravity waves following a hot Jupiter engulfment event. These findings underscore the significant role of internal gravity wave dissipation in shaping the architectures of hot Jupiter systems and provide new insights into the dynamics of planet-star interactions.

Hot Jupiter Engulfment and the Evolution of Stellar Rotation and Orbital Periods reveal complex dynamical interactions

Enhanced stellar rotation observed in stars TOI-2458 and GJ 504 is explained by the prior engulfment of a hot Jupiter planet, a process facilitated by the dissipation of internal gravity waves within the star. These groups exhibit distinct period distributions, with younger systems displaying a uniform distribution and older systems showing a marked decline in periods.

Population synthesis modelling successfully replicates the characteristics of the older hot Jupiter sample, building upon the distribution observed in the younger systems. Estimates suggest that up to 20% of main-sequence stars with masses between 0.7 and 1.5 solar masses may have engulfed a hot Jupiter during their lifetime.

The authors acknowledge that the prescriptions used for tidal dissipation are simplified, potentially influencing the precision of the results. Further investigation of orbital decay candidates is recommended to refine constraints on internal gravity wave breaking and conversion processes. Prime targets for detecting transit-timing variations include WASP-173A b, Kepler-17 b, WASP-36 b, and WASP-46 b, where efficient gravity wave dissipation could produce measurable shifts exceeding 10 seconds. These findings underscore the significant role of internal gravity wave dissipation in shaping the architectures of hot Jupiter systems and provide a new framework for understanding planetary system evolution.