As we know AGNs are considered to be one of the most luminous objects to be found in the cosmos.Based on the observer, for instance on Earth, we categorize them on the basis of the angle between the observer and the object. Suppose for instance there are two observers, one on Earth and one on some distant planet (far away from our solar system, let it be on the opposite side of the Milky Way relative to us). Would both the observers relate an AGN belonging to the same class? In other words, can these categories be relative to their viewing? Like an object can be a QSO to us but to the other observer can the same object be a Seyfert or a Blazar or an RG?

  • $\begingroup$ Short Answer: yes! Astronomical classifications are a b***h! Meaning they have blurred boundaries. $\endgroup$
    – Cheeku
    May 22, 2014 at 18:11
  • $\begingroup$ So perhaps we may be looking at the same thing after all! $\endgroup$
    – stp30
    May 22, 2014 at 18:28
  • $\begingroup$ Yeah, such problems will be significant if we ever have another observer at the said locations. $\endgroup$
    – Cheeku
    May 23, 2014 at 0:26

1 Answer 1


Yes, but most probably not in your mentioned example. You need larger distances to make a difference, I guess. However, it is by now largely accepted a unification model for AGNs, where the difference are mostly due to the angle of line of sight. enter image description here

First introduced by Urry & Padovani, then developed for further observations.

Anyway, this is only half of the truth, since the AGNs evolve, and in this evolution feedback on the host galaxy is exerted. Also, the amount of feeding/obscuring gas is varying with time (redshift) and this has to be taken into account for a correct classification. For the jets too, it is also possible that they forms only in certain stages of the AGN life... As usual in astronomy, things are much more complicated than simple catalogs/models !


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