The mystery of dark matter is a debate of astronomical proportions.

What began as an intellectual disagreement between two Georgia State astronomers in their department’s hallway has snowballed into one of the biggest questions of all: What is our universe made of?

Todd Henry and Rachel Kuzio de Naray can agree that as much as 90 percent of the cosmos is dark matter — the part of outer space that’s not illuminated — but what they can’t agree on is just what all that shadowy stuff really is.

MACHOs vs. WIMPs 2

Todd Henry (left) says dark matter is made up of MACHOs, like stars — hence his choice of shirt. Rachel Kuzio de Naray leans WIMPs, or weakly interacting massive particles.

Henry, a distinguished professor of astronomy, bets that dark matter is made up of MACHOs, or massive, compact halo objects. MACHOs can be just about any spherical object made up of atoms — stars, planets and even black holes. The reason MACHOs can’t be detected is because they’re so faint, Henry said.

Kuzio de Naray, an assistant professor of astronomy, thinks WIMPs, or weakly interacting massive particles, are the basis of dark matter.

“WIMPs are another type of subatomic particle that doesn’t interact with stuff other than gravity,” she said.

WIMPs are hypothetical, and astronomers believe WIMPs make up dark matter because, in theory, they would be heavy and move much slower than the speed of light, thus eluding a telescope.

So, it’s MACHOs versus WIMPs for what’s out there in the final frontier.

Henry and Kuzio de Naray argued their interstellar opinions Sept. 5 at the Georgia State Student Center. The debate coincided with DragonCon, the world’s largest fantasy and science fiction convention that brings thousands of costumed characters to downtown Atlanta during Labor Day weekend.

“It was a well-attended event, Mary Poppins and a chimney sweep showed up,” said Kuzio de Naray.

Heading into the showdown, Henry sized himself up as the underdog because most astronomers believe WIMPs are indeed what makes up dark matter.

“My big question is why haven’t the WIMPs found anything? It’s theoretical,” he said. “All we can say for sure is that it has gravitational pull, and that’s about it.” Henry and Kuzio de Naray concede dark matter may be a combination of MACHOs and WIMPs.

“We want it to be stars because life couldn’t exist around a WIMP,” Henry said. Kuzio de Naray countered, “But if there were no WIMPs, there’d be no stars.”

And so the debate rages on. Even the audience couldn’t pick a winner. The applause-o-meter called it a tie.