Beat Frequency Oscillations near Charged Black Holes and Other Electrovacuum Geometries

Near a charged black hole (or any other space-time permeated by a steady electromagnetic field) an electromagnetic mode oscillates in sympathy with a suitably polarized gravitational mode (and conversely). Two co-traveling modes beat against each other, exchanging totally and periodically their common energy along their history near the black hole. The black hole serves therefore as a catalyst for converting electromagnetic into gravitational radiation. Thus the effective coupling of charged matter with gravitational radiation is of the same order of magnitude as with electromagnetic radiation.