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Implications for the Hubble Constant from the First Seven Supernovae at z >= 0.35


The Supernova Cosmology Project has discovered over 28 supernovae (SNs) at 0.35 < z < 0.65 in an ongoing program that uses Type Ia SNs (SN Ia’s) as high-redshift distance indicators. Here we present measurements of the ratio between the locally observed and global Hubble constants, HL0/HG0, based on the first seven SNs of this high-redshift data set compared with 18 SNs at z ≤ 0.1 from the Calán/Tololo survey. If ΩM ≤ 1, then light-curve width corrected SN magnitudes yield HL0/HG0 < 1.10 (95% confidence level) in both a Λ = 0 and a flat universe. The analysis using the SN Ia’s as standard candles without a light-curve width correction yields similar results. These results rule out the hypothesis that the discrepant ages of the Universe derived from globular clusters and recent measurements of the Hubble constant are attributable to a locally underdense bubble. Using the Cepheid-distance-calibrated absolute magnitudes for SN Ia’s of Sandage et al., we can also measure the global Hubble constant, HG0. If ΩM ≥ 0.2, we find that HG0 < 70 km s-1 Mpc-1 in a Λ = 0 universe and HG0 < 78 km s-1 Mpc-1 in a flat universe, correcting the distant and local SN apparent magnitudes for light-curve width. Lower results for HG0 are obtained if the magnitudes are not width-corrected.

In Astrophysical Journal, 476:L63,1997

What its about

Back in the day there was a conundrum, the predicted age of the Universe based on the measured Hubble constant was younger than the oldest objects inside the Universe. One way to resolve the problem is for us to live in a part of the Universe that is less dense than average such that the galaxies used for the Hubble constant measurement are moving away from us a bit more than the overall average rate of expansion.

The above conundrum is resolved with an accelerating expansion of the Universe.

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