Unveiling The Electromagnetic Mysteries of Binary Black Holes

Credit: NASA’s Goddard Space Flight Center/Jeremy Schnittman and Brian P. Powell

Accreting black holes, which are some of the most common astrophysical systems in the universe, have been the subject of intense study for many years. A recent paper by Milton Ruiz, Antonios Tsokaros, and Stuart L. Shapiro has provided new insights into the behavior of these systems by performing general relativistic simulations of magnetized, accreting disks onto spinning binary black holes. The study focused on binary black holes with different mass ratios, observing their behavior throughout the inspiral, merger, and post-merger phases.

The researchers found that incipient jets are launched from both black holes, regardless of the mass ratio, as long as the force-free parameter in the funnel and above their poles is larger than one. At large distances, the two jets merge into a single one, which may prevent the electromagnetic detection of individual jets. As the accretion rate reaches a quasi-stationary state during pre-decoupling, the researchers observed a sudden amplification of the outgoing Poynting luminosity that depends on the mass ratio.

Following the merger, the sudden change in the direction of the spin of the black hole remnant with respect to the spins of its progenitors causes a reorientation of the jet, which drives a single, high-velocity, outward narrow beam collimated by a tightly wound, helical magnetic field that boosts the Poynting luminosity. This effect is nearly mass ratio independent. During this process, a kink is produced in the magnetic field lines, confining the jet. The kink propagates along the jet but rapidly decays, leaving no memory of the spin-shift.

The study’s findings suggest that the merger of misaligned, low-spinning, binary black hole mergers in low-mass disks may not provide a viable scenario to explain X-shaped radio galaxies if other features are not taken into account. However, the sudden changes in the outgoing luminosity at merger may help to identify mergers of black holes in active galactic nuclei, shedding light on black hole growth mechanisms and the observed co-evolution of their host galaxies.

This study contributes to a better understanding of the behavior of accreting black holes, which are fundamental objects in astrophysics. The researchers’ simulations provide new insights into the physical properties of binary black hole systems and their associated electromagnetic signatures. The insights gained from this study may help to improve our understanding of black hole growth mechanisms and the co-evolution of black holes and their host galaxies.






Source: Ruiz, Milton, Antonios Tsokaros, and Stuart L. Shapiro. “General Relativistic 
Magnetohydrodynamic Simulations of Accretion Disks around Tilted Binary Black Holes
of Unequal Mass.” (2023). https://doi.org/10.48550/arXiv.2302.09083