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Universe expanding slower than thought: Astronomers

13 April 2015 15:02


The universe may not be expanding since the Big Bang as fast as it was previously thought, astronomers say.

The discovery was made by a group of scientists at the University of Arizona and recently published via two papers in the Astrophysical Journal.

The team, headed by UA astronomer Peter A. Milne, discovered that type Ia supernovae, used to measure distances in the universe, are more diverse than formally thought, which has implications for major cosmological issues.

The use of la supernovae to measure distances was according to the view that the farther they are, they look fainter. This view is based on observations that resulted in the 2011 Nobel Prize for Physics awarded to three scientists, namely Brian Schmidt, Saul Perlmutter, and Adam Riess.

This Swift UVOT image shows galaxy M82 before the explosion and combines data acquired between 2007 and 2013. Mid-ultraviolet light is shown in blue, near-UV light in green and visible light in red. The image is 17 arcminutes across, or slightly more than half the apparent diameter of a full moon. (Credit: NASA/Swift/P. Brown, TAMU)
The Nobel laureates discovered independently that many supernovae looked fainter than the predictions since they had moved farther away from Earth than they should have done if the universe expanded at the same rate, which indicated that the rate at which stars and galaxies move away from each other is increasing.

Milne explained, “The idea behind this reasoning is that type Ia supernovae happen to be the same brightness — they all end up pretty similar when they explode. Once people knew why, they started using them as mileposts for the far side of the universe.”

“We found that the differences are not random, but lead to separating Ia supernovae into two groups, where the group that is in the minority near us are in the majority at large distances — and thus when the universe was younger,” said Milne.

“There are different populations out there, and they have not been recognized. The big assumption has been that as you go from near to far, type Ia supernovae are the same. That doesn’t appear to be the case.”
The team used data collected by NASA’s Swift satellite and Hubble Space Telescope.

“The realization that there were two groups of type Ia supernovae started with Swift data,” said Milne. “Then we went through other datasets to see if we see the same. and we found the trend to be present in all the other datasets.”

The authors conclude that some of the universe’s reported acceleration can be attributed to the color differences between the two groups of supernovae and not actual acceleration.

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