Galaxy Mrk 590 is like a radio receiver that turns its own sound on and off. Its black hole flickers between bright and dim. In 2017 it switched on again, but the VLA radio telescope heard a signal different from what was expected.
Astronomers listened to Mrk 590 four times at different frequencies. At first the signal looked like a hump, then it started to rise sharply. That happens when a plasma jet from the black hole plows into surrounding gas. The gas absorbs radio waves unevenly, changing the signal's shape.
Earlier it was unclear why the radio flare didn't coincide with the black hole's awakening. Now it's clear: they are different events. The flare was born far from the black hole, about 6 parsecs away. So different galaxies have different kinds of 'awakenings'.
The radio source in Mrk 590 at 5.75 GHz has a faint "tail" to the northeast, aligned with an outflow seen at very high resolution. If this component is moving at the speed of light, it left the core about two thousand years ago, around the time of the Roman Empire.