Through processes that aren't fully understood, some of this matter is accelerated and ejected from the black hole's poles at relativistic speeds, generating superheated streams of gas. In the case of NGC 660, its black hole is likely feeding, erupting huge streams of radio-emitting gas, but the pattern of ejected gas isn't a simple case of two hot spots blasting from two poles; there appears to be five hot spots.
"The most likely explanation is that there are jets coming from the core, but they are precessing, or wobbling, and the hot spots we see are where the jets slammed into material near the galaxy's nucleus," said Chris Salter, of Areceibo Observatory. "To confirm this, we will continue to observe the galaxy with the HSA over the next few years."
Source: NRAO Image: High Sensitivity Array (HSA) image of bright "hotspots" (inset), in galaxy NGC 660. Entire HSA image is less than a pixel in the larger optical image. Credit: Minchin et al., NRAO/AUI/NSF (HSA); Travis Rector, Gemini Observatory, AURA (optical).