### 12.2 The effective mass of Kulkarni, Chellathurai, and Dadhich for the Kerr spacetime

The Kulkarni-Chellathurai-Dadhich [244] effective mass for the Kerr spacetime is obtained from the
Komar integral (i.e. the linkage with ) using a hypersurface orthogonal vector field instead of
the Killing vector of stationarity. The vector field is defined to be , where is
the Killing vector of axi-symmetry and the function is . This is timelike outside the
horizon, it is the asymptotic time translation at infinity, and coincides with the null tangent on the event
horizon. On the event horizon it yields , while in the limit it is the
mass parameter of the solution. The effective mass is computed for the Kerr-Newman spacetime
in [106].