The Hubble constant — named after Edwin Hubble, the astronomer who found in the early 1900s that the universe is expanding — is the rate at which that expansion is occurring.
The Hubble tension arises from the fact that the observation of the local universe delivers a different value for the Hubble constant than that derived using the cosmic microwave background (CMB) — the universe's first light, which shone shortly after the Big Bang. Astronomers take CMB measurements and then wind forward using the standard model of cosmology, the so-called Lambda cold dark matter (LCDM) model.
The discrepancy has persisted even as the two separate measurement techniques have become more precise. It is troubling because it suggests that some crucial ingredient of physics is missing from our recipe for the cosmos. Hence many astronomers cite the need for a third method to help bridge this disparity, or at least shed some light on why it exists.
Two new studies suggest a new way of measuring expansion in the immediate cosmos by analyzing the motion of two nearby galaxy groups. Galaxies within these groups are simultaneously bound together by mutual gravity and dragged apart by the cosmic flow caused by the stretching of the space in which they are embedded.
Both results indicate that the universe is expanding more slowly in our vicinity than previously estimated. Not only does this technique bring measurements of the Hubble constant in the nearby universe closer in line to those made using the CMB and the LCDM model, but it also suggests that less dark matter is needed to explain cosmic observations and the dynamics of galaxies.
Source: www.space.com
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