Why does a quasar's appearance depend on the angle from which it is observed?
Shown are apparently normal, solitary galaxies (left), colliding galaxies (centre), and merging galaxies (right).
A quasar's appearance depends on the orientation of its accretion disk rotation axis relative to the observer's line of sight because of the object's complex physical structure.1
Quasars consist of several distinct components, including the central supermassive black hole, the surrounding accretion disk, high-velocity gas clouds that produce emission lines, and sometimes highly collimated radio jets of plasma. Additionally, dust-laden gas clouds located farther from the black hole can obscure the central region.1
Depending on the viewing angle, these components appear with varying degrees of prominence. For instance, the dust clouds may block the view of the inner structure from certain perspectives, while the jets or the disk itself may dominate the observation from others. Consequently, physically similar sources can manifest as a wide variety of observed phenomena depending on how they are oriented toward Earth.1