Spinning black holes reshape binary star systems in violent cosmic encounters

A new study by researchers from IIT Kanpur and the Indian Institute of Astrophysics (IIA) has explored how spinning black holes disrupt binary star systems. Their findings reveal that the black hole's spin plays a key role in shaping tidal interactions, altering everything from debris patterns to X-ray emissions.

The team focused on white dwarf binaries encountering intermediate-mass black holes, using advanced simulations to track these extreme encounters.

The research involved modelling parabolic trajectories of identical white dwarf binaries as they approached a spinning black hole. Simulations combined geodesic equations for the black hole's spin with Newtonian hydrodynamics to capture the gravitational forces at play. This approach ensured stable configurations, with deviations in viriality kept below 1%, providing a reliable framework for future studies.

The black hole's spin was found to significantly influence tidal disruption, particularly the mass fallback rate onto the black hole. In certain cases, interactions between debris from each star produced a rare three-hump structure in the fallback pattern. However, the orbital direction of the binary itself had little effect on this rate—accretion depended more on gravitational dynamics and the black hole's spin.

A critical factor emerged in the initial alignment between the binary's spin and its orbital angular momentum. This angle determined how tidal forces unfolded, affecting observable features like X-ray luminosity, spectral hardness, and the precession of relativistic jets. The study confirmed that while the black hole's spin drives disruption, the binary's inclination shapes the resulting debris and emissions.

The work builds on the Hills regime, where tidal forces from a black hole can tear apart binary systems. Here, the team demonstrated that the black hole's spin direction relative to the orbital plane influences accretion disk alignment, leading to distinct observational signatures in simulated data.

The findings provide a clearer picture of how black hole spin alters tidal disruptions in binary systems. By showing that inclination angles dictate debris behaviour and X-ray emissions, the study offers a foundation for interpreting future observations of such extreme events. The methodology's precision also opens doors for further research into astrophysical interactions in high-gravity environments.