INTERGALACTIC DUST AND THE SUPERNOVA HUBBLE DIAGRAM
ANTHONY N. AGUIRRE
Department of Astronomy, Harvard University
60 Garden St., Cambridge MA, 02138
Abstract:
Type Ia supernovae have been found to be
progressively dimmed up to redshift $z \sim 0.7$ relative to the
predictions of classic Friedmann solutions with zero cosmological
constant. This in turn would require a modification of GR, an
exquisitely tuned cosmological constant, or an equally exquisitely
tuned negative-pressure contribution to the energy-momentum tensor.
A simpler explanation of this dimming -- obscuration by a
cosmological distribution of dust -- violates theoretical constraints
derived under two assumptions: that dust is largely confined to
galaxies and/or that intergalactic dust would redden visible light in
the same way as dust in galaxies. I discuss here the possibility
that the selective destruction of very small dust grains by
sputtering in the intergalactic medium or during dust removal from
galaxies would leave an effectively uniform distribution of
non-reddening (`grey') dust that could provide an amount of dimming
at $z\sim 0.5$ comparable to the differences in $z\sim 0.5$
theoretical Hubble diagrams.