TYPE IA SUPERNOVAE AND COSMOLOGY Review paper

I discuss th eu se of Type Ia supernovae (SNe Ia) for cosmo f logica ld istance deter- minations. Low-redshift SNe Ia (z < 0.1) demonstrate that the Hubble expan- sion is linear with H0 H0 =7 2±8 km s −1 Mpc −1 , and that the properties o fd ust in other galaxies are generally similar to those of dust in the Milky Way. The light curves o fh igh -redshif t( f z = 0.3-1) SNe Ia are stretche di n a manner consis- ten tw ith the expansion of space; similarly, their spectra exhibi ts lower temporal evolution (by a factor o f f 1 + z )t han those of nearby r SNe Ia. The measured luminosity distances of SNe Ia as a function of redshift have shown that the ex- pansion of the Universe is currently accelerating, probably due to the presence of repulsive dark energy such as Einstein's cosmological constant (Λ). From about 200 SNe Ia, we find that H0 H0t0 = 0.96 ± 0.04, and ΩΛ − 1.4ΩM = 0.35 ± 0.14. Combining our data with th er esu lts o fl arge-scale structure surveys ,w e fin da best fit for ΩM and ΩΛ of 0.28 and 0.72, respectively — essentially identical to the recent WM