Fanaroff–Riley classification

Fanaroff and Riley divided this sample into two classes using the ratio of the distance between the regions of highest surface brightness on opposite sides of the central galaxy or quasar to the total extent of the source up to the lowest brightness contour.

This distinction is important because it presents a direct link between the galaxy's luminosity and the way in which energy is transported from the central region and converted to radio emission in the outer parts.

[2][3] These sources are brighter towards their central galaxy or quasar and become fainter toward the outer extremities of the lobes (also called edge-darkened).

As the galaxy moves through the cluster, the gas can sweep back and distort the radio structure through ram pressure.

This class of sources are also known as edge-brightened and are more luminous than their counterparts, with bright hotspots at the ends of their lobes.