Figure 21-21: Effect of a Black Hole’s Tidal Force on Infalling Matter A cube–shaped probe 1500 km from a 5-M_⊙ black hole. Near the Schwarzschild radius, the probe is pulled long and thin by the difference in the gravitational forces felt by its different sides. This tidal effect is a greatly magnified version of the Moon’s gravitational force on Earth. The probe changes color as its photons undergo extreme gravitational redshift and time slows down on the probe, as seen from far away.