The Accelerating Universe

The last decade has undergone a renaissance in our knowledge of the values of the basic cosmological parameters. Three new measurements combine to give a new picture of the Universe. In 1998, Adam Riess and Brian Schmidt using Type Ia supernovae measured the first indication of an accelerating expansion of the Universe (Riess 1998), the dark energy which creates the acceleration is 74% of the contents of the Universe. Recent measurements of the cosmic microwave background radiation from WMAP (Spergel 2003) shows the Universe is flat and the measurements from large-scale structure surveys (Percival 2001) and baryon acoustic oscillations (Eisenstein 2005) constrain the amount of matter in the Universe to be 26% (22% dark Matter and 4% ordinary matter). On-going research at the CFA includes a focused investigation of low redshift Type Ia supernovae (at Mt. Hopkins, MMT and Magellan telescopes) because it is the comparison of the luminosity distance vs redshift at low and high redshift that leads to the dark energy dominated cosmological picture. Also, we have a number of investigators in the ESSENCE supernova cosmology project whose aim to distinguish whether the dark energy is different from a cosmological constant at the 10% level. Our lastest findings show the data are consistent with a w = -1, flat Universe (Wood-Vasey 2007).

References:
Riess, A. G. et al 1998, AJ, 116 1009, astro-ph/9805201
Spergel, D.N. et al, 2003, ApJS, 148, 175, astro-ph/0302209
Percival, W.J. et al, 2001, MNRAS, 327, 1297
Eisenstein, D. et al. 2005, ApJ, 633, 560, astro-ph/0501171
Wood-Vasey, W. M. et al. 2007, ApJ accepted.