A new preprint making an extraordinarily high precision measurement of the Hubble constant at low z (i.e. in recent time periods) compared to the early Universe measurement, also made to high precision by Planck cosmic microwave background measurements, continues to show the discrepancy between the early time and late time measurements known as the "Hubble tension". In these measurements the late time measured values of the Hubble constant are consistently larger than those derived from the CMB in the early universe.
The increased accuracy of these late time results (i.e. low z results) strongly imply that the Hubble tension may be a real difference, in what should be a physical constant in LambdaCDM cosmology, and not just a measurement error driven discrepancy. In other words, this strengthens the case that the Hubble tension is an indication of beyond LambdaCDM physics, presumably in the cosmological constant/dark energy sector (i.e. the Lambda sector) of the "Standard Model of Cosmology". There is a considerable cottage industry already, that will surely only surge after this new result, to devise alternative theories that can explain the discrepancy.
We report observations from HST of Cepheids in the hosts of 42 SNe Ia used to calibrate the Hubble constant (H0). These include all suitable SNe Ia in the last 40 years at z<0.01, measured with >1000 orbits, more than doubling the sample whose size limits the precision of H0. The Cepheids are calibrated geometrically from Gaia EDR3 parallaxes, masers in N4258 (here tripling that Cepheid sample), and DEBs in the LMC. The Cepheids were measured with the same WFC3 instrument and filters (F555W, F814W, F160W) to negate zeropoint errors.
We present multiple verifications of Cepheid photometry and tests of background determinations that show measurements are accurate in the presence of crowding. The SNe calibrate the mag-z relation from the new Pantheon+ compilation, accounting here for covariance between all SN data, with host properties and SN surveys matched to negate differences. We decrease the uncertainty in H0 to 1 km/s/Mpc with systematics. We present a comprehensive set of ~70 analysis variants to explore the sensitivity of H0 to selections of anchors, SN surveys, z range, variations in the analysis of dust, metallicity, form of the P-L relation, SN color, flows, sample bifurcations, and simultaneous measurement of H(z).
Our baseline result from the Cepheid-SN sample is H0=73.04+-1.04 km/s/Mpc, which includes systematics and lies near the median of all analysis variants. We demonstrate consistency with measures from HST of the TRGB between SN hosts and NGC 4258 with Cepheids and together these yield 72.53+-0.99. Including high-z SN Ia we find H0=73.30+-1.04 with q0=-0.51+-0.024. We find a 5-sigma difference with H0 predicted by Planck+LCDM, with no indication this arises from measurement errors or analysis variations considered to date. The source of this now long-standing discrepancy between direct and cosmological routes to determining the Hubble constant remains unknown.
2 comments:
Both lLinks are bad here : "Prior to this result, discrepancy due to measurement errors was a much more plausible hypothesis, since there were reasons to believe that the most accurate previous late time Hubble constant measurement were understated. See also S.L.Parnovsky "Bias of the Hubble constant value caused by errors in galactic distance indicators" arXiv:2109.09645 (September 20, 2021) (Accepted for publication at Ukr. J. Phys)."
"Both lLinks are bad here" My apologies. Links cut and pasted into a post getting converted into bad links by the blogger UI interface is an ongoing problem that I'll tried to fix.
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