UNFRIENDLY TERRITORY The black hole's gravity is strong enough to warp spacetime into a 4D well, twisted by its spin. Distances are logarithmic, but the grid is not in order to make clearer where spacetime is flat or warped. N ICOLLE R . FU LLER / SAYO - A R T LLC sk yandtelescope.com * S E P TE M B E R 2 018 23http://www.skyandtelescope.com