"The science breakthrough of the year." That's how the prestigious journal Science recently described a discovery made by the High-Z Supernova Research Team, which showed that the expansion of the universe is actually accelerating. The team of 21 scientists from 10 institutions includes Craig Hogan and Christopher Stubbs, UW professors of astronomy and physics, and astronomy graduate students David Reiss and Al Dierks.

The team's findings come from studying one type of supernova, which is essentially the blast that happens when a dead star transforms into a natural thermonuclear bomb. The group has observed the supernovas' light and measured how much the light has stretched--the so-called "red shift," or elongation of the wavelengths toward the red end of the spectrum caused by expansion of the universe. The scientists also have looked at how much light has spread out and been diluted over time.

	Professors Christopher Stubbs (left) and Craig Hogan, members of the High-Z Supernova Research Team, holding light detection equipment used in their research. Photo by Mary Levin.

"We know how bright the supernovas are supposed to be," says Hogan, "so their observed brightness tells us what the universe is doing."

What they've found is that the supernovas are fainter than expected. For the light to have taken as long as it has to reach telescopes on Earth, the universe in the past must have expanded more slowly than scientists believed. In fact, it must have actually picked up speed more recently. "This can result from an exotic, little-understood force that some have mistakenly referred to as antigravity," says Hogan. "It's a component of gravity that pushes things apart instead of pulling them together. The repulsive gravity can be caused by a new form of energy that has never been observed before."

Accelerating expansion of the universe fits with the Cosmological Constant, a theory Albert Einstein formulated but later discounted as the biggest blunder of his career. However, the problem was not in the theory, says Hogan, but in Einstein's expected conclusion. He formulated the Cosmological Constant to explain a universe that neither expanded nor contracted, so the repelling gravitational force he envisioned would exactly counter the attracting gravitational force in the universe. It now appears that the repelling force is actually greater. "Even the emptiest space contains gravitational energy that helps make the universe fly apart," says Hogan. "If even empty space has energy in it, that's totally new physics--if we are right. And we might not be right."

Another team, the Supernova Cosmology Project, used different methods but reached the same conclusion as the High-Z Supernova Research Team in 1988. Both groups have published their work in scientific journals, and it is their combined work that is being hailed by Science.

The High-Z team used observatories in Chile and Hawaii to make their initial observations of supernovas. Then members used smaller telescopes around the world to monitor the stars for several weeks, until the supernova effect disappeared. Among the smaller telescopes is one at the Apache Point Observatory in New Mexico, operated by a consortium that includes the UW. A key to the project, says Hogan, is being able to make remote observations from the Apache Point telescope using the Internet. "It's the perfect tool for this kind of project," he says.

[Winter 1999 - Table of Contents]