What is a radio galaxy? What is a double radio source? Why do astronomers think these objects may be related to radioloud quasars?

A radio galaxy is an active galaxy that is very luminous at radio wavelengths, with large, bi-lobed radio structures. A double radio source or Double Radio Source Active Galactic Nuclei (DRAGN) refers to objects that have a pair of symmetrical 'lobes' or 'hotspots' of radio frequency radiation. They are thought to be powered by supermassive black holes in the centers of those galaxies. These might be related to radio loud quasars because they all show signs of active galactic nuclei with powerful jets of particles that create lobes and these jets are thought to result from processes close to a supermassive black hole at the center of the galaxy. Based on orientation, they might be observed differently and thus are oriented versions of the same parent population.