Hubble Space Telescope Captures Galactic Conjunction

Hubble Space Telescope image of spiral galaxy NGC 105. Credit: ESA/Hubble & NASA, D. Jones, A. Riess et al., Acknowledgement: R. Colombari

This image from the supernova explosions. Whilst these two phenomena may appear to be unrelated — one is a peculiar class of pulsating stars and the other is the explosion caused by the catastrophic final throes of a massive star’s life — they are both used by astronomers for a very particular purpose: measuring the vast distances to astronomical objects. Both Cepheids and supernovae have very predictable luminosities, meaning that astronomers can tell precisely how bright they are. By measuring how bright they appear when observed from Earth, these “standard candles” can provide reliable distance measurements. NGC 105 contains both supernovae and Cepheid variables, giving astronomers a valuable opportunity to calibrate the two distance measurement techniques against one another.

Astronomers recently carefully analyzed the distances to a sample of galaxies including NGC 105 to measure how fast the Universe is expanding — a value known as the Hubble constant. Their results don’t agree with the predictions of the most widely-accepted cosmological model, and their analysis shows that there is only a 1-in-a-million chance that this discrepancy was caused by measurement errors. This discrepancy between galaxy measurements and cosmological predictions has been a long-standing source of consternation for astronomers, and these recent findings provide persuasive new evidence that something is either wrong or lacking in our standard model of cosmology.