The Accelerating Universe isn't Nearly as Fast as Previously Thought

The universe is accelerating. Now, though, astronomers have discovered that it may not be accelerating nearly as fast as once thought.

For this latest study, the researchers looked at type Ia supernovae, which have been considered so uniform that astronomers call them cosmic "beacons." Surprisingly, the scientists found that these supernovae actually fall into two different populations.

"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 Peter Milne, one of the researchers, in a news 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."

The findings actually casts some light on the currently accepted view of the universe. Many supernovae appear fainter than predicted because they've moved farther away from Earth than they should have if the universe has expanded at the same rate. This means that the rate at which stars and galaxies move away from each other is increasing. However, it may not be accelerating nearly as fast as once thought.

"As you're going back in time, we see a change in the supernovae population," said Milne. "The explosion has something different about it, something that doesn't jump out at you when you look at it in optical light, but we see it in the ultraviolet. Since nobody realized that before, all these supernovae were thrown in the same barrel. But if you were to look at 10 of them nearby, those 10 are going to be redder on average than a sample of 10 faraway supernovae."

This means that some of the reported acceleration can be explained by color differences between the two groups of supernovae. This, in turn, means that the universe isn't expanding as fast as once believed.

The findings are published in The Astrophysical Journal.

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