Evidence from Type Ia Supernovae for a Decelerating, then Accelerating Universe and Dark Energy

Details Evidence from Type Ia Supernovae for a Decelerating, then Accelerating Universe and Dark Energy Evidence from Type Ia Supernovae for a Decelerating, then Accelerating Universe and Dark Energy

Apr 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004kcs..confe...6f&link_type=abstract

Presented at the KITP: Colloquium Series, Apr 21, 2004, Kavli Institute for Theoretical Physics, University of California, Santa

Physics

Scientific paper

The measured distances of type Ia (hydrogen-deficient) supernovae as a functionof redshift (z) have shown that the expansion of the Universe is currentlyaccelerating, probably due to the presence of repulsive dark energy (X) suchas Einstein's cosmological constant (Lambda). Combining all of the data withexisting results from large-scale surveys, we find a best fit for Omega_M andOmega_X of 0.28 and 0.72 (respectively), in excellent agreement with the values(0.27 and 0.73) recently derived from WMAP measurements of the cosmicmicrowave background radiation. A number of possible systematic effects (dust,supernova evolution) thus far don't seem to eliminate the need for Omega_X > 0.Most recently, analyses of supernovae at z = 1.0-1.7 reveal an early epoch ofdeceleration, followed by acceleration. Several groups are now in the processof measuring hundreds of supernovae with z = 0.2-0.8, to determine the equation ofstate of the dark energy, w_X = P/(rho c^2); thus far, the best-fit valueis w_X = -1, and the data are consistent with dw/dz = 0, suggestingthat the dark energy may indeed be the cosmological constant or somethingquite similar.

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