The increase of distance between two parts of the universe with time is referred to as the expansion of the universe. A team of astronomers has now suggested that the acceleration of the expansion of the universe may not be as fast as previously thought. This view is based on observations that resulted in the 2011 Nobel Prize for Physics awarded to three scientists, including University of Arizona alumnus Brian P. Schmidt.
The research team found that certain types of supernovae or exploding stars are more diverse than previously thought and the results have implications for big cosmological questions, such as how fast the universe has been expanding since the Big Bang. They discovered that type Ia supernovae, which have been considered so uniform that cosmologists have used them as cosmic beacons to plumb the depths of the universe, actually fall into different populations. The study findings are analogous to sampling a selection of 100-watt light bulbs at the hardware store and discovering that they vary in brightness.
Lead author Peter A. Milne said, "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 them are in the majority at large distances and thus when the universe was younger. The discovery casts new light on the currently accepted view of the universe expanding at a faster and faster rate, pulled apart by a poorly understood force called dark energy. The Nobel laureates discovered independently that many supernovae appeared fainter than predicted because 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; in other words, something has been pushing the universe apart faster and faster."
The authors concluded that some of the reported acceleration of the universe can be explained by color differences between the two groups of supernovae, leaving less acceleration than was initially reported. They also assumed that this would, in turn, require less dark energy than currently thought of.
The study has been published in the Astrophysical Journal