The Role of Wide Stellar Pairs in the Formation of Hot Jupiters around M Dwarfs ✛ ✦
Context
Hot Jupiters — giant planets with periods under 10 days — were first discovered by Michel Mayor and Didier Queloz in 1995. Since then, the transit method, perfected by David Charbonneau, has unveiled thousands of exoplanets. Yet their migration mechanisms remain debated: the high-eccentricity migration hypothesis predicts that red dwarfs with distant companions should more often host short-period giants. Testing this prediction for low-mass stars has only now become possible thanks to accumulated statistics.
Methods
The discovery of TOI-5628Ab used the transit method (TESS) and high-resolution spectroscopy (SPIRou), with radial velocities derived from the Doppler shift of spectral lines. The star's temperature was calculated using the Stefan–Boltzmann law, and Kepler's third law provided the semi-major axis estimate. For the population analysis, Gaia DR3 astrometry was used: 38 M dwarfs with confirmed hot Jupiters were selected from the catalog, and a search for co-moving companions within 100–10,000 au was performed for each, using kinematic agreement criteria; ground-based photometry was also used to refine parameters. A field sample of 546,681 TIC stars, matched in metallicity, was processed via Monte Carlo.
Results
Out of 38 systems, 13 were found to be multiple (34.2±9.5%), including TOI-5628Ab, where the companion is a white dwarf with a mass of 0.59 M⊙, signaling advanced stellar evolution. For field stars, the multiplicity was 5.3±3.7%, yielding a probability boost of 6.5 times. Estimating the Kozai-Lidov timescale showed that in 9 of the 13 systems it is less than 10 billion years — a clear sign of efficient planetary migration. Planet TOI-5628Ab has a radius of 0.74 RJ and a mass of 0.09 MJ (upper limit 0.22 MJ, 3σ).
Implications
The detected correlation at the 6.5σ level confirms that stellar companions (including white dwarfs) play a key role in shaping the hot Jupiter population around M dwarfs. This strengthens the case for high-eccentricity migration and calls for including binary systems in models of stellar evolution with planets.
Future development
The Roman Space Telescope and next-generation ground-based spectrographs will enable direct imaging of companions and high-precision spectroscopy of their atmospheres, refining masses and orbits. Large-scale surveys with PLATO will expand the sample of hot Jupiters around M dwarfs, allowing tests of migration theories.
Impact
The results will impact planet formation theory, exoplanet survey statistics, and our understanding of binary system evolution with planets.
Next steps
Detailed modeling of sample metallicity is needed, as giants prefer metal-rich M dwarfs. Measuring orbital inclinations is also required to test predictions of migration models.
Key open problems
The study tackles unsolved problems of planet formation and migration in binary systems, as well as the role of stellar evolution in the fate of planetary orbits.
The knowledge machine's view
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This paper reports the discovery of a hot Jupiter, TOI-5628Ab, orbiting an M dwarf, using the transit method (TESS) and high-resolution spectroscopy (SPIRou). Based on a sample of 38 M dwarfs hosting hot Jupiters, a search for wide stellar companions within 100–10000 AU was conducted using Gaia DR3 data, revealing a multiplicity rate of 34.2% compared to 5.3% in the field sample. It is shown that the Kozai–Lidov mechanism is effective in most multiple systems, confirming the role of distant companions in the migration of giant planets.
Where its strength is
A key strength is the direct statistical evidence linking the presence of a wide stellar companion to the occurrence of hot Jupiters around M dwarfs at the 6.5σ level. This provides solid observational support for the high-eccentricity migration scenario and opens the door to studying the evolution of such systems, including late stages with white dwarfs.
Where it could go next
- It might be interesting to compare the obtained multiplicity statistics with the results of the work on the icy origin of hot Jupiters, which shows that most such planets form beyond the snow line. A joint analysis could clarify how a wide companion triggers the migration of precisely those planets born in the cold.based on: Icy Origins: Most Hot Jupiters Come from the Cold arXiv:2607.15144
- Closely related is the study of tidal evolution of eccentric Jupiters, which details the transition from a highly eccentric orbit to a circular one under tidal forces. Applying this model to the systems in your sample would allow estimating characteristic timescales and observable orbital parameters at different stages.based on: Tidal Swings of an Eccentric Jupiter arXiv:2607.16406v1
- There is a paper in the archive showing how tidal waves can sort planets by orbital period. It would be interesting to check whether this mechanism leaves an additional imprint on the distribution of hot Jupiters in multiple M-dwarf systems.based on: How Tidal Waves Sort Planets arXiv:2606.20789
Worth trying
- Run simulations of the coupled orbital and spin evolution of the planet under tidal forces, using the approach from the paper on tidal tilting, for systems with a confirmed companion.
- Compare the metallicity of host stars in multiple and single systems from the sample to determine whether the enhanced multiplicity is a consequence of the overall chemical composition.
- Search for a correlation between the mass and orbital distance of the companion and the eccentricity of the hot Jupiter before tidal circularization—this could reveal details of the Kozai–Lidov mechanism.
Why this may matter
If it is confirmed that wide companions are the primary driver of migration, this will change how we assess the population of planetary systems around M dwarfs, especially in the context of habitable zones. Understanding migration pathways is also crucial for interpreting future data from the PLATO and ARIEL telescopes.
Nearby works in our archive
- Tidal Swings of an Eccentric Jupitersimilarity 0.70
- How Tidal Waves Sort Planetssimilarity 0.64
- How Giant Planets Kept Their Rapid Spinsimilarity 0.61
- How to Hear a Planet Near a Dead Starsimilarity 0.60
- Catching a Sunset on a Distant Planetsimilarity 0.60
- Icy Origins: Most Hot Jupiters Come from the Coldsimilarity 0.59
The archive is crowded around this work: 1 review nearby, closest at 0.70. This ground is well walked — and there is plenty to compare against.
Original abstract
as written by the authors arXiv:2607.10177
Binary stars are ubiquitous, yet it remains unclear how wide-orbit stellar companions influence the formation of hot Jupiters, particularly around M dwarfs. Here, we first report the discovery of TOI-5628Ab, a giant planet transiting a mid-type M dwarf ($$M_\ast=0.36\pm0.02\ M_\odot$$) every 4.34 days, accompanied by an associated white dwarf TOI-5628B ($$M_{\rm WD}=0.59\pm0.16\ M_\odot$$) at a projected distance of about 2,500 AU. Using TESS, ground-based photometry and SPIRou RVs, we constrain the planet radius to $$0.74\pm0.04\ R_J$$ and mass to $$0.09\pm0.04\ M_J$$, with a $$3\sigma$$ upper limit of $$0.22\ M_J$$. Building on this system, we further conduct a homogeneous systematic search for co-moving stellar companions with projected semi-major axis between 100 and 10,000 AU around all M dwarfs with confirmed giant planets with periods smaller than 10 days and radii larger than 0.7 $$R_J$$, as well as a group of field M stars with stellar properties similar to the planet sample, based on the stellar kinematics from Gaia DR3. We measure a stellar multiplicity of $$34.2\pm9.5\%$$ for M dwarfs hosting short-period giant planets, which is substantially higher than the fraction of $$5.3\pm3.7\%$$ for the field M stars by approximately a factor of 6. Our results suggest that wide-orbit stellar companions tend to promote the formation of short-period giant planets around M stars with masses $$0.21 \leq M_\ast\leq 0.64\ M_\odot$$, and high-eccentricity migration may play an important role in producing such systems.
The white dwarf TOI-5628B has cooled for just 0.53 billion years, while its progenitor lived for 2.5 to 6.9 billion years — meaning the red giant phase and envelope ejection happened after the planet formed, so we're seeing a system that survived a cataclysm.
The TOI-5628 system is reminiscent of Tatooine from Star Wars, but the second component is a dead star, adding drama. In Dan Simmons' novel Hyperion, worlds are lit by dying suns, creating a similar atmosphere.
Key numbers
- multiplicity of systems with hot Jupiters: 34.2%
- multiplicity of field M dwarfs: 5.3%
- probability boost factor: 6.5
- period of planet TOI-5628Ab: 4.34 days
- projected separation to companion TOI-5628B: 2500 au