Question

If there was a lot of interstellar dust between a supernova and us, how would that affect the observed brightness of the supernova(compared to the brightness of the supernova in the absence of dust)?

Would the distance to a dust-obscured supernova be measured to be too high or too low (assuming no correction was made for the presence of the dust)?

Since interstellar dust might make the calculated distances to some SNe incorrect (which would result in bad determinations of H0, etc.), how can astronomers recognize and correct for the effect that dust has on observed brightness?

Answer 1

If there is a lot of dust between us and supernova then the supernova will appear dimmer as the light is scattered by the dust particles.

However shorter wavlengths are scattered more hence the supernova will appear redder, this is called interstellar reddening. This will cause distance of the supernova to be estimated more than actual distance. This is also due to dimmer appearance of the supernova. Hence distance of dust-obscured supernova will be measured too high.

Reddening ratio is calculated from primarily photographic light curves, determined by reddened and unreddened stars. Reddening ratios are also calculated due to observation of colour and luminosity. The difference in reddening ratios can be used to determine the properties of dust and hence corrections in observed brightness can be made.

The reddening ratios can be corrected and used to calculate log(H0) which can be used to calculate the corrected distance.