Largest Map of Universe Yet Bolsters Theories about Dark Energ
- From: Sam Wormley <swormley1@xxxxxxxxx>
- Date: Tue, 23 May 2006 13:48:57 GMT
SCIENCE NEWS
May 17, 2006
Largest Map of Universe Yet Bolsters Theories about Dark Energy
http://www.sciam.com/article.cfm?chanID=sa003&articleID=00054F9D-371E-146A-B71E83414B7F0000
Using the light of distant, dying galaxies, astronomers have produced
the largest, three-dimensional map of the universe yet. Encompassing
roughly 600,000 so-called luminous red galaxies--ancient galaxies with
only old, red stars left that are uniquely brilliant--the map extends
5.6 billion light-years out into space, or 40 percent of the way to the
edge of the visible universe.
Astrophysicists Nikhil Padmanabhan of Princeton University and David
Schlegel of Lawrence Berkeley National Laboratories led a team of
international colleagues that painstakingly surveyed the color and
redshift of 10,000 of these unique galaxies. Using data from the Sloan
Digital Sky Survey in New Mexico and from a telescope in Australia, the
researchers were able to map a fan-shaped slice of the cosmos that
covers a tenth of the sky in the Northern Hemisphere. They then applied
these measurements to the broader sample to create their
three-dimensional map.
"There's statistical uncertainty in applying a brightness-distance
relation derived from 10,000 red luminous galaxies to all 600,000
without measuring them individually," Padmanabhan admits. "The game we
play is, we have so many that the averages still give us very useful
information about their distribution."
With such a measure of the distribution of matter, the researchers
could test a proposed ruler based on regular variations in the grouping
of ordinary matter every 450 million light-years or so. "Unfortunately,
it's an inconveniently sized ruler," Schlegel says. "We had to sample a
huge volume of the universe just to fit the ruler inside."
By showing such regular variations, the map confirms theories about
dark energy--a mysterious force that accounts for the acceleration of
the universe's expansion. As expected, its influence is outsized,
making up nearly 75 percent of the universe's density. "By looking at
where density variations were at the time of the cosmic microwave
background and seeing how they evolve into a map that covers the last
5.6 billion years, we can see if our estimates of dark energy are
correct," Padmanabhan notes. Now the astronomers just need to make even
more precise maps--hard to do when so much of the matter is in the
dark. The research is slated to appear in an upcoming issue of Monthly
Notices of the Royal Astronomical Society. --David Biello
.
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