General relativity's no-hair theorem says a rotating black hole is fixed by mass and spin alone (the Kerr metric), but extra fundamental fields could give black holes additional 'hair.' The gravitational-decoupling method generates such hairy modifications by adding a new gravitational source to a seed Einstein solution. This paper computes the observational signatures of a geometrically thin accretion disk around the rotating hairy black hole obtained this way. Using the standard relativistic thin-disk (Novikov-Thorne-type) model, the authors numerically evaluate the disk's radiative flux, temperature, and differential luminosity as functions of radius, and they render the disk's bolometric image with a ray-tracing (null-geodesic) code. Comparing against the Kerr metric, they find the hairy black hole's disk signatures deviate most from Kerr in the rapidly rotating case and in the inner region of the disk, offering an observational handle to test for black-hole hair in near-term astronomical observations.
General relativity's no-hair theorem says a rotating black hole is fixed by mass and spin alone (the Kerr metric), but extra fundamental fields could give black holes additional 'hair.' The gravitati…