Dirac quasinormal frequencies of the Kerr-Newman black hole

The Dirac quasinormal modes (QNMs) of the Kerr-Newman black hole are investigated using continued fraction approach. It is shown that the quasinormal frequencies in the complex ω plane move counterclockwise as the charge or angular momentum per unit mass of the black hole increases. They get a spiral-like shape, moving out of their Schwarzschild or Reissner-Nordström values and “looping in” towards some limiting frequencies as the charge and angular momentum per unit mass tend to their extremal values. The number of the spirals increases as the overtone number increases but decreases as the angular quantum number increases. It is also found that both the real and imaginary parts are oscillatory functions of the angular momentum per unit mass, and the oscillation becomes faster as the overtone number increases but slower as the angular quantum number increases.