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.