A black hole can torment a star for years, rather than rip it apart immediately. Tidal forces are when the hole's gravity stretches the star: the near side is pulled harder than the far side. Usually, getting too close rips the star apart instantly — that's a tidal disruption event. But if the star stays a bit farther out, the critical tear doesn't happen. Instead, like a rubber band that snaps after many gentle tugs, the star wears down bit by bit, losing mass in chunks. Each loss is a brilliant flare.
The flares can flicker unpredictably: not every pass strips material, so the signals come and go. That explains the odd behavior of the source J0456-20. A similar instability was described almost a century ago by Subrahmanyan Chandrasekhar for white dwarfs — stellar remnants that can't grow beyond a limit. Now the same principle links energy dissipation in the star with black hole flares.
as written by the authors arXiv:2603.27132
A repeating partial tidal disruption event (rpTDE) is typically modeled as a star on a bound orbit that is partially disrupted by a massive black hole (MBH) at each pericenter passage. For disruption to occur, the pericenter distance must be close to or within the characteristic tidal radius, such that the tidal field overcomes the star's binding force and triggers mass loss. However, a binary with a pericenter distance several times the tidal radius can build up its tidal perturbation over multiple orbits via a diffusive process, eventually triggering a nonlinear instability that ejects mass and powers an eruption. This leads to repeated, stochastic disruptions. In this Letter, we propose that such a mechanism can produce a subclass of rpTDEs with large variations in recurrence time (e.g., J0456-20), which we dub ``diffusive-tide rpTDEs''. We show that diffusive tidal growth can occur for a white dwarf or main-sequence star orbiting a MBH when the pericenter distance is a few times the tidal radius, provided that the orbital period is shorter than the tidal energy dissipation timescale. These diffusive-tide rpTDEs may account for a significant fraction of the rpTDE population.
If the Sun were in that star's place, each flare would shine brighter than our entire Galaxy — and it would last for centuries.
Like in 'Interstellar': Gargantua's tidal forces slowly wrecked planets in its orbit.