Thin accretion disk around a Kerr black hole immersed in swirling universes

Abstract

We have studied the properties of thin accretion disks around swirling-Kerr black holes, which own an extra swirling parameter describing the rotation of the immersed universe. Our results show that the swirling parameter leaves distinct imprints on the energy flux, temperature distribution and emission spectra of the disk and gives rise to some new effects that differ from those induced by the black hole's spin. With the increasing of the swirling parameter, both the energy flux and radiated temperature in the disk increase in the inner region where circular orbital radii are smaller and decrease in the outer region where circular orbital radii are larger. In contrast, these quantities consistently increase with the black hole's spin. Although the swirling parameter and the black hole's spin parameter lead to higher cut-off frequencies, the background swirling reduces the observed luminosity of the disk at lower frequencies and enhances it only at higher frequencies, which is quite distinct from that of the black hole's spin. Furthermore, the conversion efficiency increases with the black hole's spin parameter, but decreases with the swirling parameters. Additionally, the effects of the swirling parameter are found to be suppressed by the black hole's spin parameter. These results could help us further understand the properties of thin accretion disks and the swirling of the universe background.