The Shape of the Kα Line as a Possible Indication of the Black Hole Existence

Observations of Seyfert galaxies in X-ray region reveal the wide emissive lines in their spectra, which can arise in inner parts of accretion disks, where the effects of General Relativity (GR) must be counted. A spectrum of a solitary emission line of a hot spot in Kerr accretion disk is simulated, depending on the radial coordinate r and the angular momentum a = J/M of a black hole, under the assumption of equatorial circular motion of a hot spot. It is shown that the characteristic two-peak line profile with the sharp edges arises at a large distance, (about r ≈ (3 - 10) r_g). The inner regions emit the line, which is observed with one maximum and extremely wide red wing. High accuracy future spectral observations, being carried out, could detect the angular momentum a of the black hole.