Part of the book: Aspects of Today's Cosmology
Astronomers continue the search for better a Hubble-Lemaitre constant, H0, value and other cosmological parameters describing our expanding Universe. One investigative school uses ‘standard candles’ to estimate distances correlated with galactic redshifts, which are then used to calculate H0 and other parameters. These distance values rely on measurements of Cepheid variable stars, supernovae types Ia and II or HII galaxies/giant extra-galactic HII regions (GEHR) or the tip of red giant star branch to establish a distance ‘ladder’. We describe some common pitfalls of employing log-transformed HII/GEHR and SNe Ia data rather than actual distances and suggest better analytical methods than those commonly used. We also show that results using HII and GEHR data are more meaningful when low quality data are discarded. We then test six important cosmological models using HII/GEHR data but produce no clear winner. Groups utilising gravitational waves and others measuring signals from the cosmic microwave background are now at odds, ‘tension’, with those using the SNe Ia and HII data over Hubble-Lemaitre constant values. We suggest a straightforward remedy for this tension.
Part of the book: Cosmology 2020