Kepler-56 is a red giant star, its outer layer spins faster and at a different orientation than its core.
Kepler-56’s fast spin cannot be explained just by the tidal pull of its two known planets. Two known planets orbiting Kepler-56 are too far away and too light to transfer enough angular momentum (AM) to make the star’s outer layer spin so fast.
Unusually fast rotation of the envelope and misaligned its core and envelope spin of star Kepler-56 might be due to the star once swallowing a close-orbiting hot Jupiter giant planet. It's called planetary engulfment.
Tidal torque depends on star radius and mass, orbital period, planet mass, Tidal quality factor Q.
Equation of Angular momentum gained by the star when it engulfs
Researchers used-
MESA code (Modules for Experiments in Stellar Astrophysics) to track how the star’s structure and rotation evolve,
Tidal interaction equations to estimate angular momentum transfer from known planets,
Engulfment simulation to calculate spin-up from swallowing a planet,
Obliquity damping to Study how the spin tilt changes with time.
Source: https://arxiv.org/html/2510.25680v1
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