Dark Energy--Now in a Neighborhood Near You

Astrophysicists in recent years have found evidence for a force they call “dark energy” in observations from the farthest reaches of the universe, billions of light years away.

Now an international team of researchers has used data from powerful computer models, supported by observations from the Hubble Space Telescope, to find evidence of dark energy right in our own cosmic neighborhood.

	A supercomputer-produced cross-section of part of the universe shows galaxies as brighter dots along filaments of matter, with a sea of dark energy filling in between the galactic islands. Image from James Wadsley, McMaster University.

The data paint a picture of the universe as a virtual sea of dark energy, with billions of galaxies as islands emerging from the sea, says Fabio Governato, a University of Washington research associate professor of astronomy and the first recipient of the Astronomy Department’s Brooks Prize, a post-doctoral fellowship in theoretical astrophysics. Governator is also a researcher with Italy’s National Institute for Astrophysics.

In 1929 astronomer Edwin Hubble demonstrated that galaxies are moving away from each other, which supported the theory that the universe has been expanding since the big bang. In 1999 cosmologists reported evidence that an unusual force, called dark energy, was actually causing the expansion of the universe to accelerate.

However, the expansion is slower than it would be otherwise because of the tug of gravity among galaxies. As the battle between the attraction of gravity and the repellent force of dark energy plays out, cosmologists are left to ponder whether the expansion will continue forever or if the universe will collapse in a “big crunch.”

In 1997, Governato designed a computer model to simulate evolution of the universe from the big bang until the present. His research group found the model could not duplicate the smooth expansion that had been observed among galaxies around the Milky Way, the galaxy in which Earth resides. In fact, the model produced deviations from a purely radial expansion that were three to seven times higher than astronomers had actually observed, Governato says.

" The observed motion was small, and we could not duplicate it without the presence of dark energy,” he says. “When we added the dark energy, we got a perfect match.”

Governato and his research colleagues from Switzerland and Sweden are part of an international research collaboration called the N-Body Shop, which originated at the UW and ran simulations of universe expansion on powerful supercomputers in Italy and Alaska. Their findings provide supporting evidence for a sea of dark energy surrounding galaxies.

“We studied the properties of galaxies close to the Milky Way instead of looking billions of light years away,” Governato says. “It’s like traveling from Seattle to Portland, Oregon, rather than from Seattle to New York, to measure the Earth’s curvature.”

[Summer 2005 - Table of Contents]