Intermittent black hole jets are like a 'cosmic volcano'

When astronomers look out into the cosmos, they see supermassive black holes (SMBH) in two different states. In one state, they're dormant. They're actively accreting only a tiny amount of matter and emit only faint, weak radiation. In the other, they're more actively accreting matter and emitting extremely powerful radiation. These are normally called active galactic nuclei (AGN).