America
Our universe is not accelerating as fast as thought
Washington, April 12
Providing clues to
understanding cosmological questions like how fast the universe has been
expanding since the Big Bang, a team of astronomers, including an
Indian American, has identified two distinct types of supernovaes.
A
University of Arizona-led team of astronomers has discovered that
certain types of supernovae, or exploding stars, are more diverse than
previously thought.
The findings hint at the possibility that the
acceleration of the expansion of the universe might not be quite as
fast as textbooks say.
The team 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.
"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 A. Milne, astronomer at University of Arizona.
"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," pointed
out Milne.
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.
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 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.
Milne and his
co-authors, including Indian-American Gautham Narayan of the National
Optical Astronomy Observatory, or NOAO, in Tucson, observed a large
sample of type Ia supernovae in ultraviolet and visible light.
For their study, they combined observations made by the Hubble Space Telescope with those made by NASA's Swift satellite.
Some
of the reported acceleration of the universe can be explained by colour
differences between the two groups of supernovae, leaving less
acceleration than initially reported, concluded the team.
The results appeared in the Astrophysical Journ