Probing Rotating Einstein-Power-Yang-Mills Black Holes through Shadows and Quasinormal Modes: Prospects for Event Horizon Telescope Constraints

Abstract

Within Einstein power-Yang-Mills gravity (EPYM), we build a rotating black hole via the Newman-Janis procedure applied to the spherically symmetric static seed, obtaining a Kerr-like metric controlled by the spin \(a\), the magnetic Yang-Mills charge \(Q\), and the power parameter \(q\). We analyse the horizon structure and the photon region, and we compute the shadow as it appears to a remote observer for different values of these parameters. Using the published Event Horizon Telescope measurements of M87\(^*\) and Sgr A\(^*\), we constrain the Yang-Mills charge and the power parameter from the angular size and the Schwarzschild deviation \(δ\) of the observed images. At the Maxwell point \(q = 1\) the spin marginalized likelihood combining both sources bounds the charge to \(Q \lesssim 0.26\,M\) at \(1σ\), while the fixed-spin band intersection at \(a = 0.7\,M\) gives the weaker \(Q \lesssim 0.52\,M\) from the M87\(^*\) angular size alone. The bound weakens as \(q \to 3/2\), where the shadow diameter becomes nearly insensitive to the charge. The shadow radius also fixes the limiting absorption cross section at high frequencies and hence the energy emission rate, which is suppressed by the charge, enhanced by the power parameter, and suppressed at near-extremal spin. We then compute the quasinormal modes of a massless scalar on the rotating background from the leading-order Wentzel-Kramers-Brillouin (WKB) conditions on the Teukolsky type radial potential, finding that the oscillation frequency rises and the damping rate falls as the charge or spin increases. The power parameter leaves an imprint on the shadow size and its charge sensitivity and in the quasinormal spectrum the shift is in principle present but lies below the resolution of current detectors.