This study aims to measure the rate at which the Universe is expanding (the Hubble constant) to a higher precision than has been achieved before. Until recently, measurements of the Hubble constant from different techniques - comparing how the apparent brightness and size of astronomical objects change as they get further away from Earth - gave consistent results. However, as measurements have become more precise these different techniques have now diverged. If this divergence is real it will have profound implications for our understanding not just of cosmology, but of fundamental physics concepts such as 'how many fundamental particles exist?'.
Currently the 'tension' in these measurements is large enough to be statistically significant, but given the dramatic implications, further independent verification is required before it is confirmed that the tension is real. The research in this program will provide an independent measurement of the Hubble constant using observations of 'standard candles' - objects whose intrinsic brightness can be used to infer their distance - with a precision that makes it directly comparable to measurements from the competing 'standard ruler' technique.
We will tackle the problem using variable stars; stars whose intrinsic brightness are directly related to their pulsation period. Until now, standard practice has been to analyse variable star data one wavelength at a time, making comparisons with theoretical models after the fact (if at all). The technique proposed here takes advantage of the vast amount of data we have today, using all available data on a set of stars, combined with stellar models, to ensure that our measurements are as accurate and precise as possible.
By including all available data in the analysis, we will reduce the uncertainty in our measurement of the standard candle Hubble constant. Only then can we determine whether or not the differences in recent Hubble constant measurements are due to experimental error, or if we need to rethink what we know about our Universe.