Hubble Finds the Universe Is Expanding Faster Than Previously Thought

June 6, 2016 | Johannes Van Zijl

NASA image of a galaxy
Photo credit: NASA, ESA, and L.Frattare (STScl)

The finding may provide important clues for understanding dark energy, dark matter and dark radiation!

Using NASA’s Hubble Space Telescope, a team of astronomers have evidence that the universe is expanding 5 to 9 percent faster than previously thought.

The astronomers, led by Adam Riess of the Space Telescope Science Institute and The Johns Hopkins University, redefined the current expansion rate of the universe, which is known as Hubble’s constant.  They found that the rate at which the universe is expanding is actually 73.2 kilometres per second per megaparsec (a distance equal to 3.26 million light-years).

“This surprising finding may be an important clue to understanding those mysterious parts of the universe that make up 95 percent of everything and don’t emit light, such as dark energy, dark matter, and dark radiation,” Riess said in a news release.

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The discovery was achieved by measuring the distances of 2,400 Cepheid stars in 19 galaxies beyond the Milky Way using the Hubble Space Telescope. Cepheid stars exhibit a direct relationship between the pulses they emit and their brightness, providing astronomers with a unique opportunity to precisely calculate their distances from Earth.

The astronomers then compared these distances to the expansion of space, which can be calculated by measuring how light from galaxies is stretched as the source moves away from Earth. Using these two values, they came up with the new expansion rate which is more accurate than previous estimates, with only 2.4 percent uncertainty.

However, the new discovery provides a mystery: the rate at which the universe is expanding does not match predictions based on the radiation left over from the Big Bang nearly 13.8 billion years ago.  

“If we know the initial amounts of stuff in the universe, such as dark energy and dark matter, and we have the physics correct, then you can go from a measurement at the time shortly after the Big Bang and use that understanding to predict how fast the universe should be expanding today,” said Riess. “However, if this discrepancy holds up, it appears we may not have the right understanding, and it changes how big the Hubble constant should be today.”

Some possibilities have already been put forward that could account for the discrepancy in the expansion rate of the universe. These include unseen matter in the universe called dark matter, as well as mysterious dark energy, a repulsive anti-gravity force believed to account for up 70 percent of all the energy in universe. Or there could be something wrong with Einstein’s theory of general relativity, the astronomers noted in their news release.

“We know so little about the dark parts of the universe, it’s important to measure how they push and pull on space over cosmic history,” said study co-author, Lucas Macri of Texas A&M University in College Station.

Astronomers will continue to refine the accuracy and reduce the uncertainty in the prediction of the expansion rate of the universe. The James Webb Telescope, which is due for launch in late 2018, will be a handy tool to help astronomers make better measurements of the universe’s expansion.

The findings will be published in the upcoming edition of The Astrophysical Journal.

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