The sudden appearance of dust in the early Universe
  Observations suggest that high-redshift galaxies are either very dusty or
essentially dust free. The evolution from one regime to the other must also be
very fast, since evolved and dusty galaxies show up at redshifts corresponding
to a Universe which is only about 500 Myr old. In the present paper models
which predicts the existence of an apparent dichotomy between dusty and
dust-free galaxies at high redshift are considered. Galaxies become dusty as
soon as they reach an evolved state and the transition is very rapid. A special
case suggests that while stellar dust production is overall relatively
insignificant -- contrary to what has been argued recently -- it can at the
same time be consistent with efficient dust production in supernovae in the
local Universe. Special attention will be given to the recent discovery of a
dusty normal galaxy (A1689-zD1) at a very high redshift z = 7.5 +/- 0.2.
