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New Distance Measurements Intensify Mystery of Universe’s Expansion Rate

Scientists have obtained the most precise measurements yet of a nearby galaxy cluster’s distance, adding compelling evidence that the Universe is expanding faster than our current physics models can explain. The findings, published January 15 in The Astrophysical Journal Letters, deepen a cosmic mystery that has challenged astronomers for over a decade.

Using light from exploding stars in the Coma galaxy cluster, researchers measured its distance at 98.5 million parsecs (about 320 million light-years) from Earth. This measurement aligns with historical estimates but provides unprecedented precision, achieved by analyzing 13 supernovae within the cluster.

“This cluster is in our backyard, it has been measured long before anyone knew how important it was going to be,” said Dan Scolnic, associate professor of physics at Duke University and the study’s lead author.

The new findings contribute to what astronomers call the “Hubble tension” – a discrepancy between two ways of measuring how fast the Universe is expanding. When researchers use the new Coma cluster distance to calibrate measurements from the Dark Energy Spectroscopic Instrument (DESI), they find the Universe is expanding at 76.5 kilometers per second faster for every megaparsec (about 3.26 million light-years) of distance.

This result significantly differs from predictions based on observations of the early Universe, which suggest a slower expansion rate of about 67.4 kilometers per second per megaparsec. The difference between these values, while seemingly small, poses major challenges for our understanding of physics.

“The tension now turns into a crisis…. We’re at a point where we’re pressing really hard against the models we’ve been using for two and a half decades, and we’re seeing that things aren’t matching up,” Scolnic explained. “This may be reshaping how we think about the Universe.”

A Cluster in Our Cosmic Neighborhood

The Coma cluster, containing thousands of galaxies, serves as a crucial cosmic milestone for measuring distances in the Universe. The research team identified 32 supernovae within the cluster, ultimately using 13 that met strict quality criteria for their calculations.

The team’s distance measurement agrees with decades of previous studies using various methods, but achieves two to three times better precision. This agreement with historical measurements while using different techniques strengthens confidence in the results.

Looking Ahead

The findings suggest the disconnect between theoretical models and observations may be more pervasive than previously thought. Future observations using the James Webb Space Telescope and improved supernova measurements could help resolve this growing tension in our understanding of the cosmos.

“There are still surprises left in cosmology,” Scolnic noted, “and who knows what discoveries will come next?”

The research was supported by the Templeton Foundation, the Department of Energy, the David and Lucile Packard Foundation, the Sloan Foundation, the National Science Foundation and NASA.


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