The blazar main sequence

We propose a sequence ( the blazar main sequence: BMS) that links the two main components of the blazar class, namely, flat-spectrum radio quasars (FSRQs) and BL Lac objects, and yields all their distinctive features in a correlated way. In this view, both types of sources are centered on a supermassive Kerr hole close to maximal spin and observed pole-on. However, the FSRQs are energized by accretion at rates (m) over dot similar to 1-10, and are dominated by disk components ( thermal and electrodynamic jetlike components) that provide outputs in excess of L similar to 10(46) ergs s(-1). On the other hand, accretion levels (m) over dot << 1 are enough to energize BL Lac objects; here the radiation is highly nonthermal, and the power is partly provided by the rotational energy of the central Kerr hole, with the latter and the disk together sustaining a typical L similar to 10(44) ergs s(-1) for several gigayears. If so, we expect the BL Lac objects to show quite different evolutionary signatures from the FSRQs, and in particular, number counts close to the Euclidean shape, or flatter if the sources make a transition to a BL Lac from an FSRQ mode. In addition, for lower (m) over dot along the BMS, we expect the large-scale electric fields to be less screened out and to accelerate fewer particles to higher energies radiating at higher frequencies; so in moving from FSRQs to BL Lac objects, these nonthermal radiations will peak at frequencies inversely correlated with the disk output. For the BL Lac objects, such a dependence implies increased scatter when one tries a correlation with the total output. At its endpoint, the BMS suggests widespread objects that are radiatively silent but still efficient in accelerating cosmic rays to ultrahigh energies.