Nearby, “Normal” Galaxies

In 1964 shortly after the discovery of quasars, George Field, then at Princeton, was impressed by the fact that the high redshift of quasars implied that they must be prevalent in the past – that very possibly they were associated with galaxy formation and not the end of a long process of galaxy evolution. He wrote a paper, now largely forgotten, entitled “Quasi-stellar radio sources as spherical galaxies in the process of formation.” This was before the popularity, or even the respectability, of the black hole scenario, so Field's picture was that a collapsing protogalaxy could form a dense spheroidal cloud in which star formation would be rapid. This would lead to a quasar luminosity and flux variations due to frequent supernovae. He even pointed out that the density of quasi-stellar sources could be consistent with the present observed density of spheroidal galaxies. In many ways this was a very prescient contribution, but now we know that the energy source is likely to be accretion onto black holes, and the black holes do not disappear. They remain in the center of most reasonably massive galaxies as a generally quiet quasar remnant (Lynden-Bell's idea), waiting there to flare occasionally when a morsel of food drifts by.