A direct way to measure the distances of galaxies

Abstract

The distances to external galaxies can be estimated directly from the light echoes of historical supernovae, under suitable circumstances. The maximum degree of polarization for likely scattering functions occurs for 90 deg scattering, and hence if an appropiate scattering medium is present, a circle of highly polarized light would be observable at a metric radius of ct, where t is the time since the historical supernova. Measurement of the angular size of this ring yields the distance without any intermediate or secondary calibrators. If the scattering angle of maximum polarization is not 90 deg, but is known, then the method may still be used. With a refurbished Hubble Space Telescope (HST) it should be possible to use this method to distances well in excess of the distance to the Virgo cluster. Caveats include the uncertain form of actual or apparent scattering functions, and certain geometrical configurations for the scatterers which may give results that are misleading if incomplete information is available, and the polarized ring may be faint or partial in extent.