The acceleration of the universe may not be as great as previously estimated, according to a recent study from the University of Arizona. The new research shows that a method used for measuring distances to other galaxies may not be as reliable as once believed.
Type Ia supernovae Type Ia supernovae are typically used to gauge distances to far-flung galaxies. These events occur in binary star systems that include a white dwarf – the remains of a dead stellar body once possessing the mass of our own sun – and a larger companion. Material spirals off the larger star, collecting around the smaller body. When a critical mass is reached, the gas and dust explode in a brilliant flash.
Astronomers believed that these events release a precise amount of energy, allowing researchers to easily calculate their distance from Earth. However, the new investigation reveals that type Ia supernovae come in two varieties, and the ratio between these varieties is different closer to our galaxy than farther away. This suggests that astronomers may be inaccurately measuring distances to these star systems — throwing off the measurement of the universe's acceleration.
"There are different populations out there, and they have not been recognized," said Peter Milne, an astronomer at the University of Arizona. "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."
Dark energy is a mysterious force that most astrophysicists consider responsible for pushing the universe apart at an ever-accelerating rate. The new study, which examined type Ia supernovae in visible and ultraviolet light, could greatly affect this theory.
Some supernovae appeared dimmer than calculations would suggest if the universe were expanding at a constant rate. Researchers believe this could be due to an ever-increasing rate of acceleration as galaxies, and the stars within them, move away from one another.
Hubble Space Telescope (HST) images taken in visible light were combined with ultraviolet data from the Swift satellite in order to study the violent stellar outbursts. Because light only travels at a finite speed, astronomers see distant bodies – such as galaxies – as they were in the past. More distant objects are seen as they were further in the past than those closer to Earth.
"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."
While light from some populations were shifted to the blue end of the spectrum, others leaned toward red. In order to better understand the impact of the study's findings – and its meaning for measures of dark energy – more research will have to be conducted.
The study of type Ia supernovae was detailed in a pair of papers published in the Astrophysical Journal.
Photo: NASA Goddard Space Flight Center | Flickr
