Hubble measurements confirm that the universe is expanding about nine percent faster than expected, based on how the Universe appeared shortly after the Big Bang over 13 billion years ago.
Using new data from NASA‘s Hubble Space Telescope, astronomers have significantly lowered the possibility that this discrepancy is a fluke, down from 1 in 3,000 to only 1 in 100,000. Or a new physics may be needed to better understand the cosmos, said Adam Riess, a Professor of physics and astronomy at Johns Hopkins University and Nobel Laureate.
This was done by observing pulsating light from 70 stars nearly 200 000 light-years from earth, called the Large Magellanic Cloud, a satellite galaxy of the milky way, floats in space, in a long and slow dance around our galaxy.
The scientists used a new technique, called drift and shift (DASH), that uses the Hubble as a ‘point-and-shoot’ camera to look at groups of Cepheids stars. The way they could measure at the same amount of time all 70 stars then it would normally take to observe just one. This technique can also help measure the distances across space and reflect how fast the cosmos is expanding as time passes, a value known as the Hubble constant.
Previous observations measurements map a remnant afterglow from the Big Bang known as the Cosmic Microwave Background, which helps scientists to predict how the early Universe would likely have evolved into the expansion rate astronomers can measure today.
In 2016 and 2017 astronomers discovered that the Universe is expanding between five and nine percent faster than previously calculated reducing the uncertainty to only 2.4 percent. Prof. Riess’s research has reduced the uncertainty to an unprecedented 1.9 percent.
The new estimate of the Hubble constant is 74.03 kilometers per second per megaparsec, while previous observations of the early Universe, gives a value of 67.4 kilometers per second per megaparsec.
“The Hubble tension between the early and late Universe may be the most exciting development in cosmology in decades,” said Prof. Riess “This mismatch has been growing and has now reached a point that is really impossible to dismiss as a fluke. This disparity could not plausibly occur by chance.”
Because cosmological models suggest that observed values of the expansion of the Universe should be the same as those determined from the Cosmic Microwave Background, new physics may be needed to explain the disparity. “Previously, theorists would say to me, ‘it can’t be. It’s going to break everything.’ Now they are saying, ‘we actually could do this,'” Riess said.
Various scenarios have been proposed to explain the discrepancy, but there is yet to be a conclusive answer. An invisible form of matter called dark matter may interact more strongly with normal matter than astronomers previously thought. Or perhaps dark energy, an unknown form of energy that pervades space, is responsible for accelerating the expansion of the Universe.
Although Riess does not have an answer to this perplexing disparity, he and his team intend to continue using Hubble to reduce the uncertainty in their measure of the Hubble constant, which they hope to decrease to 1 percent.