Alumni CLASnotes Spring 2006
In This Issue:

The Dark Side of Astronomy

This story is about two big things you’ve never seen.

Big Thing Number One

Astronomer Anthony Gonzalez and the bullet cluster that is proving the existence of dark matter.
Astronomer Anthony Gonzalez and the bullet
cluster that is proving the existence of dark
is dark matter: that elusive, hard-to-detect material that, according to some scientists, makes up the bulk of the universe. If current theories are to be believed, science has, until very recently, completely lost track of about 85 percent of everything that exists.

Big Thing Number Two

is the work of UF astronomer Anthony Gonzalez, who is part of a team that last year offered the first concrete proof that dark matter is more than just theory. The research of UF physicist Tarek Saab might just close the case, offering incontrovertible proof that most of the universe is unseen.

So why didn’t you hear about this find—potentially the weightiest result ever to come out of astrophysics? It made a blip in The New York Times and The Washington Post, and Discover named it one of the top three science stories of 2006. Maybe the news was buried under stories of war, elections, and the birth of celebrity babies.

In case you missed it (and we’re obviously assuming you did) Gonzalez and colleagues published a paper in The Astrophysical Journal Letters that has the astronomy community in a buzz. Using data from their observations of the collision of two galaxies known as the “bullet cluster,” the team—led by Doug Clowe at the University of Arizona at Tucson—provided the most compelling evidence for the existence of dark matter, actually observing dark matter and “normal” matter separating during the celestial event.
So what is dark matter? It’s not a simple thing to explain.

Since the days of Copernicus, man has explored the universe with a telescope in one hand and a calculator in the other. Okay, so Copernicus didn’t have a calculator exactly, but he did observe the heavens and generate mathematical formulas to describe the motions he saw there. Those formulas would help him predict where he could find a certain star in the future. When those predictions didn’t match what he saw in his telescope, Copernicus would change his formulas—and the theories that went with them.

This went on happily—though hardly uneventfully—until about 40 years ago, when scientists started taking a hard look at the way distant galaxies move. They began to notice that galaxies didn’t move in the ways they were expected to: they moved like they were ten times heavier.

Something was drastically wrong. Either the scientists’ math was way off base, or the research community had simply missed about 85 percent of the stuff in the universe.

“The basic idea now is normal, everyday matter—like the paper on your desk—is only a small fraction of the matter in the universe,” said Gonzalez. “So this combined with all the electrons, protons and neutrons makes up about 15 percent of what’s out there and the ultimate question is what is the rest?”

Categorized as “dark matter” because it is invisible to even the most advanced equipment in modern technology, scientists can barely agree that it exists, much less reach a decision about what it is exactly. This is where the work of aforementioned physics professor Tarek Saab comes in.

Physicist Tarek Saab in his underground lair.
Physicist Tarek Saab in his underground research lair.
Saab travels beneath the surface of the earth—a half-mile down, deeper than the bats—to find a substance from outer space. As a member of the Cryogenic Dark Matter Search, he is collaborating with 50 other scientists from ten universities across the U.S. in an effort to detect dark matter interacting with other particles. The researchers work in an old Minnesota mine, which filters out the distracting cosmic rays and radioactive particles dancing around on the earth’s surface.

“It’s just a very fancy sieve,” Saab said. “The energy we need to observe is so small we have to use devices that are cooled down to absolute zero and eliminate all background noise to make it more readily measurable.”

The goal of Saab’s work is to prove the existence of dark matter on earth by measuring the energy produced from its interaction with atoms. Using the trusty billiard ball analogy, Saab described how atoms and particles bounce off one another much like balls in a game of pool. As dark matter bumps into atoms, Saab hopes to measure the thermal energy coming off of the invisible substance and therefore prove its existence.

The field of dark matter science is not one without controversy. As recently as the November 21 issue of the Monthly Notices of the Royal Astronomical Society, astronomers like University of Waterloo researchers John Moffat and Joel Brownstein attempt to debunk the existence of dark matter by holding to a longstanding theory that there is no invisible matter in our universe, only a miscalculation in the way we understand gravity.

You are probably asking yourself why scientists are spending so much time and grant money studying a particle for which they can’t even reach a consensus on whether or not it exists. The answer is simple—if dark matter does exist, a big piece of the puzzle in understanding our universe will fall into place. The impact of such a discovery could lead to unprecedented advancements in medicine and science.

When asked why they are dedicating their careers to such a frustrating, elusive topic—and whether it will make any real difference in the lives of people if they ever are successful—Gonzalez and Saab like to quote a pioneer in the study of electricity, Michael Faraday, who, when questioned by the British prime minister in the 1800s about the value of his work, had the following response:

“Sir, I do not know, but some day you will tax it.”

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