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We compute the time evolution of a Kerr (rotating) black hole which is immersed in a perturbing scalar field, uniform at large distances from the hole. The perturbing field produces a torque on the hole which (i) is perpendicular to the field lines; (ii) causes the perpendicular component J of the hole's angular momentum to decrease exponentially with time J1 = (Ji) i exp (- t/T), r = (3c5/8irG) X (mass of hole)-2 X (energy density of field)-1, bringing the hole's total angular momentum J into eventual alignment with the field; and (iii) accomplishes this alignment by converting rotational energy of the black hole into irreducible mass. We conjecture extensions of these results to black holes perturbed by external electromagnetic or gravitational fields. According to these conjectures "spin-orbit coupling" in a binary star system should not remove a significant fraction of a black hole's intrinsic angular momentum during the system's lifetime against gravitational-radiation damping.
William H. Press (1972) studied this question.