A giant planet circles too close to its star. With each orbit, it tugs on the star with its gravity, and waves are born deep inside the star, like ripples from a stone dropped into water. These waves damp the planet's orbit, and it spirals into the star. The star swallows the planet and starts spinning faster.
Stellar rotation is the key clue. Scientists took two fast-spinning stars, TOI-2458 and GJ 504, and showed that their speeds are explained by the recent ingestion of a hot Jupiter. Such planets are gas giants the size of Jupiter but orbiting closer to their star than Mercury is to the Sun. Tidal forces inside the star act like a brake: waves in its interior dissipate the orbital energy, and the planet slowly but surely spirals inward.
The researchers built a computer model that reproduces the observed orbital distribution. They estimate that up to 13% of stars with masses between 0.7 and 1.5 solar masses that once had a hot Jupiter have already swallowed it. This changes our picture of how often stars devour their planets and explains why some stars spin unexpectedly fast.
Thus, tidal waves inside stars rewrite the fates of planetary systems. A hot Jupiter, born far from its star, migrates inward and then perishes in the star's depths. Having swallowed a planet, the star spins faster, and astronomers see this trace.
A hot Jupiter can be swallowed by its star in a few million years — a blink of an eye compared to the star's age of billions of years.
In the movie 'Interstellar', Miller's planet orbits so close to a black hole that tidal forces raise giant waves — here, the star's tidal forces, in contrast, damp the planet's orbit.