4 ms·
Cosmology standard candle not so standard after all
- InclinedPlane 16y agoThis happened before, the relationship between Cepheid luminosity and variation period were worked out with nearby stars that we could measure distance to via parallax. This relationship was used to determine the distance to nearby galaxies and thus establish the basic foundation of the scale of the Universe (e.g. determining the value of the Hubble constant, etc.) However, it turns out there are actually two types of Cepheids and they do not have the same relationship between period and luminosity. This meant that measurements of distances to neighboring galaxies were wrong, since they included a mixture of classical and Type II Cepheids. Fixing that error led to adjustments to the estimated distance to neighboring galaxies by a factor of 4, and a comparable increase in the age and size of the Universe. This solved a fundamental problem at the time, whereby the Earth was older than the Universe (since we can measure the age of the Earth via radiological dating of Uranium, for example). Note that today we have multiple methods for determining the age of the Universe (such as type Ia supernovae, study of the cosmic microwave background, etc.) so this revelation is unlikely to change that, though it's likely to have other implications in our understanding of cosmology.