A team of astronomers have determined the universe may not be expanding quite as quickly as previously believed, based on observations of young supernovae.

The University of Arizona (UA) team reported their findings in two studies published in the Astrophysical Journal. The studies focus on the diversity of supernovae in the universe and their implications on its expansion.

"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," Peter A. Milne, an associate astronomer in the UA's Department of Astronomy and Steward Observatory, said in a press release. "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."

Supernovae occur when stars explode and often act as magnifying glasses that allow astronomers to see objects deep in space that a telescope may otherwise not be able to spot. The researchers compared the diversity of supernovae to how different light bulbs can vary in brightness.

The study also challenges the 2011 Nobel-Prize-winning findings of three astronomers who determined a force called dark energy was hastening the expansion of the universe.

"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," Milne said. "The faraway supernovae should be like the ones nearby because they look like them, but because they're fainter than expected, it led people to conclude they're farther away than expected, and this in turn has led to the conclusion that the universe is expanding faster than it did in the past."