'Dark matter' is cosmic mystery

Paolo Gondolo and his colleagues have drawn a map that may lead scientists to treasure: the answer to one of the most perplexing unknowns in the universe.

A team of researchers is looking for proof of the existence of mysterious tiny particles, using the suggestions of Gondolo, an assistant professor of physics at the University of Utah. The answer may come in about a year.

Astronomers have measured the motion of stars in other galaxies, those immense "island universes" scattered across the heavens. They calculated the total mass of everything that can be seen in galaxies. They know that in order to keep a star locked in place, the gravitational pull of any galaxy must reach a certain level.

But the galaxy's mass is not enough, when all visible matter is accounted for.

"We find that there is a deficit," Gondolo said.

"The mass of all the stars (in a galaxy) is just about a tenth of the mass that would keep the stars in their orbits."

What makes up the missing 90 percent? Because we can't see it, scientists call it "dark matter."

Many cosmologists think much of the mass is in the form of countless subatomic particles that don't interact easily with normal matter. Because they are hard to detect, they are invisible to us, but they still have mass.

If galaxies have enough of these particles, that could provide the gravity needed to keep the stars in their orbits.

The name for this postulated form of material is WIMPs, for weekly-interacting massive particles. An enormous number of them may form a halo of material in and surrounding our galaxy.

Although WIMPs are extremely hard to detect, they may not be impossible to find.

For a decade, a team of scientists in Gondolo's native Italy, collaborating with Chinese researchers, has been carrying out a detection project called DAMA, for Dark Matter Search. (He is not part of this team.)

DAMA uses extremely pure crystalline scintillators in a laboratory underground where normal background radiation would not set off the detectors.

"Some time ago, they have detected a signal that they claim may be due to dark matter WIMPs," Gondolo said in a telephone interview. "It is not clear that the signal they see is due to WIMPs."