The use of Type Ia supernovae (SNe Ia) as distance indicators remains essential for the study
of the expansion history of the universe and for explorations of the nature of dark energy.
Unless properly corrected for, the existence of intergalactic dust will introduce a redshift
dependent magnitude offset to standard candle sources. This would lead to overestimated
luminosity distances compared to a dust-free universe and bias the cosmological parameter
estimates as derived from observations of SNe Ia.
We model the optical extinction and X-ray scattering properties of intergalactic dust
grains to constrain the intergalactic opacity using a combined analysis of observed quasar
colours and measurements of the soft X-ray background.
Furthermore, a lack of understanding of the progenitor systems and the empirically derived
colour-brightness corrections represent severe limitations for SNe Ia as cosmological probes.
A direct confirmation of the single-degenerate progenitor scenario would be the detection of
circumstellar material arising from the transfer of matter to the white dwarf by its binary
companion star. Dust, that may reside in the circumstellar environment, would have important
implications for the observed colours of SNe Ia.
We present far-infrared observations of two SNe Ia (SNe 2011by and 2011fe) obtained
with the Herschel Space Observatory, aiming to confirm, or possibly reject, circumstellar dust
as an explanation for the observed colours of SNe Ia.
