Dusty nature of quasars

The most characteristic property of active galaxies, including
quasars, are prominent broad emission lines. These lines allowed to
discover the cosmological nature of quasars, and at present they
provide the most convenient method of weighting black holes residing
in their nuclei.  However, a question remains why such strong lines
form there in the first place.

I will discuss an interesting possibility that dust is responsible for
this phenomenon. The dust is known to be present in quasars in the
form of a dusty/molecular torus which results in complexity of the
appearance of active galaxies. However, this dust is located further
from the black hole than the Broad Line Region.  We propose that the
dust is present also closer in and it is actually responsible for
formation of the broad emission lines. The argument is based on
determination of the temperature of the disk atmosphere underlying the
Broad Line Region: it is close to 1000 K independently from the black
hole mass and accretion rate of the object. The mechanism is simple
and universal but leads to a considerable complexity of the active
nucleus surrounding. I will conclude with the discussion how this idea
fits into the general scheme of the quasar structure.