Colloquium

Fundamentals of Supernova Cosmology

Robert P. Kirshner
Clowes Professor of Science
Harvard University

Wednesday, October 7, 2009   4:00 p.m.  NSH 118

(Refreshments at 3:30 p.m. NSH 202)

 

Since the surprising discovery of cosmic acceleration in 1998, subsequent observations of the cosmic microwave background and the large-scale distribution of galaxies have converged on a picture in which the universe has ~2/3 dark energy and ~1/3 dark matter. Ordinary baryons, lost in the round-off error, are only about 4% of the mass-energy in the universe.  Over the past decade, larger samples of supernovae have made the existence of this negative-pressure component of the universe more secure. Now our effort has shifted to determining the properties of the dark energy. Alas, theory has nothing much to offer as a plausible hypothesis to test. One simple question seems worth answering: "Is dark energy a constant, like a modern version of Einstein's cosmological constant, or has it changed over cosmic time?"  Supernova samples are now large enough that systematic errors dominate over statistical uncertainties, so better understanding, not just a larger sample, is required to make progress on this question. The largest systematic errors in supernova distances come from the pernicious effects of interstellar dust absorption. New observations carried out at near-infrared wavelengths promise to reduce these errors and lead to a more certain knowledge of the nature of dark energy. This talk will sketch the present constraints on dark energy, illustrate how these can be improved with near-infrared measurements of supernovae, and speculate on the best strategy for future measurements with the proposed Joint Dark Energy Mission.

 

Host: Peter Garnavich