New measurement of universe's expansion rate is 'stuck in the middle' | 7/8/2019 | Staff
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A team of collaborators from Carnegie and the University of Chicago used red giant stars that were observed by the Hubble Space Telescope to make an entirely new measurement of how fast the universe is expanding, throwing their hats into the ring of a hotly contested debate. Their result—which falls squarely between the two previous, competing values—will be published in the Astrophysical Journal.

Nearly a century ago, Carnegie astronomer Edwin Hubble discovered that the universe has been growing continuously since it exploded into being during the Big Bang. But precisely how fast it's moving—a value termed the Hubble constant in his honor—has remained stubbornly elusive.

Hubble - Constant - Scientists - Universe - History

The Hubble constant helped scientists sketch out the universe's history and structure and an accurate measurement of it might reveal any flaws in this prevailing model.

"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 lead author Wendy Freedman of the University of Chicago, who began this work at Carnegie.

Tools - Universe - Rate - Expansion - Results

Until now, there have been two primary tools used to measure the universe's rate of expansion. Unfortunately, their results don't agree and the tension between the two numbers has persisted even as each side makes increasingly precise readings. However, is possible that the difference between the two values is due to systemic inaccuracies in one or both methods, spurring the research team to develop their new technique.

One method, pioneered at Carnegie, uses stars called Cepheids, which pulsate at regular intervals. Because the rate at which they pulse is known to be related to their intrinsic brightness, astronomers can use their luminosities and the period between pulses to measure their distances from Earth.

Bells - Listening

"From afar two bells may well appear to be the same, listening...
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