Spinning black holes twist binary stars into chaotic debris patterns

A new study has explored how spinning black holes disrupt binary star systems in unexpected ways. Researchers from IIT Kanpur and the Indian Institute of Astrophysics (IIA) used simulations to track the behaviour of white dwarf pairs encountering a moderately massive, rotating black hole. Their findings reveal that the black hole's spin can produce unusual patterns in the debris left behind after tidal disruption.

The team focused on identical white dwarf binaries following parabolic paths around a spinning black hole. Using theoretical models and simulations, they integrated geodesic equations for the black hole's rotation alongside Newtonian hydrodynamics for the stars. This approach allowed them to study how the black hole's spin alters the tidal forces acting on the binary system.

One key discovery was the emergence of a three-hump structure in the fallback rate of tidal debris. This rare pattern arises from the complex interactions between debris streams from each star. The shape and timing of these humps depend on the initial alignment between the binary's spin and its orbital angular momentum.

The simulations also showed that the orbital direction—whether prograde or retrograde—plays a critical role. Prograde orbits, where the binary moves in the same direction as the black hole's spin, lead to faster circularisation of debris. This results in a smoother, earlier peak in the fallback rate. In contrast, retrograde orbits cause prolonged collisions between debris streams, delaying and sharpening the fallback profile.

Even at a distance of 25 gravitational radii from the black hole, the effects of spin were pronounced. The study's methodology ensured stable white dwarf configurations, with viriality deviations kept below 1%. This precision sets a foundation for deeper investigations into tidal disruption events.

The research highlights how black hole spin reshapes the dynamics of binary star disruptions. By influencing debris patterns and fallback rates, it introduces richer physics than non-spinning black holes would produce. These findings provide new insights for future studies on tidal interactions in extreme gravitational environments.