Supernovae, Dust, and Cosmology

Supernova of type Ia, exploding white dwarfs near the Chandrasekhar limit of 1.4 solar masses, have gained tremendous importance due to their utility as cosmological distance indicators. Observations of these events have revealed the unexpected and astonishing discovery of an accelerating Universe. The interpretation and the use of type Ia supernovae as standard candles is, however, not without problems. One of the largest corrections and also largest uncertainty is the correction for dust attenuation caused by dust grains possibly located in the interstellar medium of the host galaxy. An additional, and largely neglected problem arises from light scattered on dust grains which are distributed in interstellar dust clouds in the line of sight between observer and supernova. Based on a model of self-gravitating clouds we discuss the contribution of the scattered light on the supernova light curves and will show how the distance estimates to the supernova events are affected using standard estimation tools. It is shown based on simple statistical considerations that dust scattered light might cause a serious problem if a significant fraction of the supernova events are interspersed within the in-homogenous dusty medium.