Cosmologists have puzzled over discrepancies in the measurement of the Hubble constant (67.4 km/sec/Mpc vs. 74.0 km/sec/Mpc), with some claiming that there is something fundamentally wrong with our picture of the universe. From a report on a new study at ScienceDaily:
“The Hubble constant is the cosmological parameter that sets the absolute scale, size and age of the universe; it is one of the most direct ways we have of quantifying how the universe evolves,” said Freedman. “The discrepancy that we saw before has not gone away, but this new evidence suggests that the jury is still out on whether there is an immediate and compelling reason to believe that there is something fundamentally flawed in our current model of the universe.”
In a new paper accepted for publication in The Astrophysical Journal, Freedman and her team announced a new measurement of the Hubble constant using a kind of star known as a red giant. Their new observations, made using Hubble, indicate that the expansion rate for the nearby universe is just under 70 kilometers per second per megaparsec (km/sec/Mpc). One parsec is equivalent to 3.26 light-years distance.
This measurement is slightly smaller than the value of 74 km/sec/Mpc recently reported by the Hubble SH0ES (Supernovae H0 for the Equation of State) team using Cepheid variables, which are stars that pulse at regular intervals that correspond to their peak brightness. This team, led by Adam Riess of the Johns Hopkins University and Space Telescope Science Institute, Baltimore, Maryland, recently reported refining their observations to the highest precision to date for their Cepheid distance measurement technique. Paper. (open access) – Wendy L. Freedman, Barry F. Madore, Dylan Hatt, Taylor J. Hoyt, In-Sung Jang, Rachael L. Beaton, Christopher R. Burns, Myung Gyoon Lee, Andrew J. Monson, Jillian R. Neeley, Mark M. Phillips, Jeffrey A. Rich, Mark Seibert. The Carnegie-Chicago Hubble Program. VIII. An Independent Determination of the Hubble Constant Based on the Tip of the Red Giant Branch. The Astrophysical Journal (accepted), 2019 More.
The new study got a Hubble constant of 69.8 km/sec/Mpc: “But the results do not appear to strongly favor one answer over the other say the researchers, although they align more closely with the Planck results.” So if there is something fundamentally wrong with our picture of the universe, there still is, more or less, and we will have to live with it for now.
See also: We actually don’t know the precise value of the Hubble constant.
New Findings: Discrepant Values In Universe’s Expansion Make Everything Murkier
and
Is Cosmology “In Crisis” Over How To Measure The Universe?