Kerr Black Holes, Spin & Frame Dragging: Physical Mechanisms

A Kerr black hole is characterized in classical general relativity by mass and angular momentum. Outside the horizon lies an ergoregion where spacetime rotation is so strong that no observer can remain stationary relative to distant space. The radius of the innermost stable orbit depends strongly on whether orbiting matter moves with or against the spin.

Rotating mass drags local inertial frames, an effect called frame dragging. Near a rapidly spinning black hole, this alters orbital frequencies and precession. Electromagnetic fields in magnetized plasma can couple to the rotating spacetime and help power jets by extracting rotational energy.

Relativistic X-ray reflection spectra, continuum fitting, quasi-periodic timing behavior, and horizon-scale observations constrain spin-dependent accretion geometry. Frame dragging has also been measured weakly around Earth, confirming the underlying relativistic effect outside the black-hole regime.

Rotating mass drags local inertial frames. Close to the hole, this changes precession and stable-orbit radii. Magnetic fields threading the rotating system may extract spin energy electromagnetically to help power jets.