What is the cause of the intense luminosity of active galaxies, such as quasars or seyferts?

Accretion of material due to supermassive black holes in galactic cores leads to intense active galaxies luminosity.

The center of the galaxies has a high luminosity as compared to other parts postulated to be emitted by something other than the stars because of its intense luminosity. They are electromagnetic radiation source which is useful for discovering objects from outer space.  

They can be observed by gamma rays, ultra-violet, radio, microwave, x-rays, infrared, and many more similar. Classification of an active galactic nucleus which is based on their observed characteristics has been made and the quasar is the powerful one.  

d. stage 4

explanation:

the existence of some kind of demographic transition is widely accepted in the social sciences because of the well-established historical correlation linking dropping fertility to social and economic development.[1] scholars debate whether industrialization and higher incomes lead to lower population, or whether lower populations lead to industrialization and higher incomes. scholars also debate to what extent various proposed and sometimes inter-related factors such as higher per capita income,lower mortality, old-age security, and rise of demand for human capital are involved.[2]