The abstract reads:
We argue that the Ice Cube, a neutrino telescope under construction at the South Pole, may test the hypothesis of the gravitational repulsion between matter and antimatter. If there is such a gravitational repulsion, the gravitational field, deep inside the horizon of a black hole, might create neutrino-antineutrino pairs from the quantum vacuum. While neutrinos must stay confined inside the horizon, the antineutrinos should be violently ejected. Hence, a black hole (made from matter) should behave as a point-like source of antineutrinos. Our simplified calculations suggest, that the antineutrinos emitted by supermassive black holes in the centre of the Milky Way and Andromeda Galaxy, could be detected at the Ice Cube.
I had never thought about this question. But it may be that in the far, far future (after all the stars die) that our descendants (probably machines?) orbit around black holes to capture the energy in the antineutrinos being ejected.
(By the way, where would the energy come from, the black hole or the "quantum vacuum" itself?)