A study performed by a team of scientists led by a Vanderbilt University physicist now confirms that the universe is not only expanding but expanding at an increasing rate.
“As far as the ultimate fate of the universe goes, the most straightforward conclusion is that over the next few billion years, it is going to become an increasingly thin, cold and boring place,” says Robert Knop.
Knop is the assistant professor of physics and astronomy at Vanderbilt University who led an analysis of supernova data for the Supernova Cosmology Project (SCP), a group effort of 48 international scientists who did the study at the Lawrence Berkeley National Laboratory in California.
The results will appear in the Astrophysical Journal. The study also provides insights into the nature of the recently recognized and little understood force called dark energy implicated in the expansion. The study reveals that the universe is comprised of anywhere from 68 to 81 percent dark energy and 19 to 32 percent miscellaneous matter.
The study also gives a more accurate measure of just how effective dark energy is at pushing the universe apart. The study measured 11 exploding stars spread throughout the universe, made visible by the Hubble Space Telescope. Using the Hubble, Knop and his colleagues measured the light curves of exploding stars, called a Type 1A supernova that occur in star systems made up of a normal star and a collapsed star called a white dwarf.
The white dwarf pulls matter from its companion until it reaches a critical size when it is consumed in a thermonuclear explosion. The brightness of the explosion provides a dependable gauge of their distance. The new findings back up the initial discovery made five years ago that the expansion rate of the universe appears to be speeding up rather than slowing down.
David F. Salisbury, assistant director of the Office of Science & Research Communications at Vanderbilt, said most of the impact of the expansion would not be seen or felt for hundreds of millions of years.
“The first sort of visible impact it should have in the future is that gradually the sky would get darker because of these distant objects. Once they start receding at more than the speed of light they essentially disappear from the sky,” Salisbury said. One of the criticisms of the initial studies, performed with ground telescopes, was the possibility that dust from distant galaxies may have dimmed the images of the supernova explosions enough to skew their results. Because the supernova images obtained by the Hubble Telescope are unaffected by the earth’s atmosphere, they are not only sharper, their colors are more accurate.
“Limiting such uncertainties is crucial for using supernovae-or any other astronomical observations-to explore the nature of the universe,” said Ariel Goobar, a member of SCP and a professor of particle astrophysics at Stockholm University in Sweden.
Astronomers can get a good estimate of the distance of a supernova by comparing its brightness with those of comparable stellar outbursts that have taken place near it. The dimmer the image the greater the distance, because it takes light time to travel intergalactic distances. As astronomers look further out into the universe, they are also looking back in time.
By COLLEEN CREAMER
For The Nashville City Paper
