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R. P. Kirshner (Harvard-Smithsonian CfA)
The High-Z Supernova Search Team is an international collaboration formed to measure the deceleration and global geometry of the Universe using Type Ia supernovae. Our group is a collection of more than 20 astronomers from 11 institutions on 4 continents with one goal.
Our published work analyzes a sample of 16 high-z supernovae and makes a surprising conclusion. Barring unaccounted-for systematic effects, the Universe appears to be accelerating. Since matter can only slow the expansion, some other component, such as a non-zero cosmological constant, must be counteracting gravity. Our supernova observations, when combined with current cosmic microwave background anisotropy measurements, are consistent with a Universe with Euclidean global geometry which is dominated at the present epoch by something very much like a cosmological constant.
Our latest observations, obtained from the ground and with HST, extend these early results. Now attention must shift to the possible systematic errors in our methods. Can absorption by dust, a drift in stellar populations, or the effects of chemical evolution be responsible for our conclusions? These possiblities can be examined by careful analysis of low-z supernovae, theoretical modelling, and further work on the high-z sample. The cleanest test will be observing the change in apparent magnitude with redshift for z = 1. The predictions of cosmology and of most systematic effects should be quite distinct.
Further information can be found at the High-Z Team website: http://www-cfa.harvard.edu/cfa/oir/Research/supernova.html
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