“Hubble tension becomes Hubble crisis”: New measurement deepens mysterious gap

Using new data, a research team has once again measured the speed at which the local universe is expanding and obtained a value that further deepens a mysterious discrepancy. The so-called "Hubble tension" is now becoming a "Hubble crisis", says physicist Dan Solnic, who led the analysis. By this he means that the values for the expansion speed of the universe in the near and distant cosmos now appear to be drifting even further apart. In a way, this means "that our cosmological model could be broken", adds Solnic.

A particularly precise basis

As Duke University in the USA explains, Solnic and his team have used the data from the Dark Energy Spectroscopic Instrument (DESI) to measure the distance to one of the closest galaxy clusters to us even more precisely than was previously possible. The DESI measures tens of millions of galaxies for a huge 3D map of the universe. Solnic realized that its data could also be used to determine the distance to the so-called Coma galaxy cluster with particular precision. That's why he dropped everything to work on it around the clock, says the physicist.

Using 12 type Ia supernovae, he and his team were then able to calculate that the galaxy cluster is 320 million light years away – pretty much in the middle of the values collected so far. Based on this precise distance in the comparatively nearby universe, the team was then able to recalibrate the so-called cosmic distance ladder and arrived at a value of 76.5 km/sec/Mpc for the so-called Hubble constant. This is once again considerably higher than the values previously determined for the local universe, and thus even more clearly above the particularly precise value determined by the Planck space telescope for the early universe (just over 67 km/sec/Mpc).

Mysterious discrepancy keeps cosmology busy

The Hubble constant (H₀) is a fundamental quantity in cosmology. The value indicates the speed at which an object at a distance of one megaparsec (3.26 million light years) is moving away from us due to the expansion of the universe alone (the Andromeda Galaxy, for example, is around 0.89 megaparsec away from us). The constant was first calculated by the US astronomer Edwin Hubble, whose name it now bears. Although the measurements have become increasingly accurate in recent years, they have not provided a consistent value. Instead, a mysterious discrepancy has emerged that has become one of the most exciting questions in cosmology today.

The work by Solnic's team, which has now been published in the Astrophysical Journal Letters, underlines the impression that has long been emerging that the cause of the “Hubble tension” lies in the models themselves, writes the university. “We've come to a point where we're really pushing the models we've been using for two and a half decades and realizing that things don't fit,” Solnic says. What comes out of this could change our idea of the universe, “and that's exciting”. The physicist is delighted that cosmology still holds many surprises.

(mho)