Galactic Center filaments are large, radio-emitting, filament-shaped structures found in the Galactic Center of the Milky Way. Their cause is unknown. Both vertical and horizontal filaments exist, running perpendicular and parallel to the galactic plane, respectively, away from the Galactic Center. Vertical filaments possess strong magnetic fields and emit synchrotron radiation: radiation emitted by particles moved at near-lightspeed through a magnetic field. Although theories have been proposed, the source of these particles is unknown. Horizontal filaments appear to emit thermal radiation, accelerating thermal material in a molecular cloud. They have been proposed to be caused by the outflow from Sagitarius A*, the Milky Way's central black hole, impacting vertical filaments and H II regions of ionized gas around hot stars.