Quasar continuum spectrum disfavors black holes with a magnetic monopole charge

Abstract

Black holes carrying a magnetic monopole charge have been a subject of interest for a long time. In this work we explore the possibility of an observational evidence of such black holes carrying a magnetic monopole, namely the Bardeen rotating black holes. We derive the theoretical spectrum from the accretion disk surrounding a Bardeen black hole using the thin-disk approximation. We compare the theoretically derived spectrum with the optical data of eighty Palomar Green quasars to constrain the monopole charge parameter $g$ and the spin parameter $a$ of the quasars. From our analysis we note that the Kerr-scenario in general relativity is observationally more favored than black holes with a monopole charge. We arrive at such a conclusion using error estimators like ${\ensuremath{\chi}}^{2}$, the Nash-Sutcliffe efficiency, the index of agreement and their modified forms. In particular, black holes with $g\ensuremath{\ge}0.03$ (in the unit of the black hole mass) is outside 99% confidence interval. The implications are discussed.