The peak luminosity of a white dwarf supernova is around 1010LSun, and it remains above 108 LSun for about 150 days. In comparison, the luminosity of a bright Cepheid variable star is about 10,000LSun. The Hubble Space Telescope is sensitive enough to make accurate measurements of apparent brightness for Cepheid variables at distances up to about 100 million light-years. Estimate the distance of a fading white dwarf supernova of luminosity 108 LSun whose apparent brightness is comparable to that of a bright Cepheid variable star 100 million light-years from Earth. How does your distance estimate compare with the size of the observable universe?