Quasars and Active Galaxies

What determines the luminosity of an AGN?

Sometimes the amount of intervening material—either in our galaxy, or in the AGN host galaxy—can diminish the amount of light we see from an active nucleus. That does not affect, however, the AGN’s luminosity, or the total amount of energy that it emits. The single most important determinant of an AGN’s luminosity is the rate at which matter falls toward its central supermassive black hole. Low-luminosity AGNs might have only a few Earth-masses’ worth of material falling onto the central black hole per year. The most luminous AGNs, on the other hand, are accreting (gathering mass by infalling matter) at a rate equivalent to swallowing a million Earths per year.


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