College of Science

Gamma-rays and galactic mysteries: Clemson astrophysicist studies dark matter’s secrets


Antonio Circiello is an expert in the unknown.

In our vast universe, only 15% of all matter is known or seen. The other 85% is known as dark matter and is still mysterious even to scientists. 

Circiello, a graduate research assistant in the Department of Physics and Astronomy at Clemson University, recently presented his research on dark matter at the American Physical Society’s April meeting, one of the largest conferences in the field.

head shot of a man with black hair wearing a black suit coat, white shirt with unbuttoned collar and tie
Antonio Circiello

“Dark matter is matter. That’s one of the only concrete things we know about it,” said Circiello. “It’s one of the biggest mysteries in the universe at present. We know that a large portion of the universe is made of dark matter, but we don’t know what it is. We don’t know its nature.”

But how do we know dark matter exists if we can’t see it?

Dark matter is still matter, meaning it has gravitational pull. The main visible effect of the presence of dark matter is its gravitational attraction.

The research Circiello presented built on that done by colleague Alex McDaniel, which explored new ways by which to detect dark matter. Some of the best targets are nearby, dark-matter-dominated galaxies. 

Among the closest

The systems Circiello is studying are known as UFCSs (ultra-faint compact stellar systems). These are satellites of the Milky Way that are very faint in the optical band and could be among the closest dark matter-dominated objects we know of. 

Within those UFCSs, researchers are looking for gamma-rays. Gamma-ray emissions are significant because they can indicate the presence of dark matter. When two dark matter particles collide, a phenomenon known as annihilation may occur. This annihilation may produce gamma rays, allowing scientists to probe the nature of dark matter.

Promising lead

“The goal of our study is to determine the potential of the UFCSs to constrain the properties of dark matter,” Circiello said. “In our paper, we show that if these systems are confirmed to contain dark matter, they will improve the current constraints by a significant amount, and in the best-case scenarios, they can serve as a check on a very promising lead for dark matter signal, which is the galactic center excess.”

The galactic center excess is a large emission of gamma rays located in the center of the Milky Way, of yet unknown origin, that studies suggest could be ascribed to dark matter annihilation.

Despite the limitations that current technology has when it comes to dark matter research, Circiello’s work highlights the need for continued exploration. Circiello’s findings concluded that the observed systems could put the strongest constraints so far on the properties of dark matter.

“I’m glad that our work has been able to put a spotlight on these systems, because they really are quite interesting,” said Circiello. “We wanted to stimulate further observations to determine the nature of the UFCSs, by showing how appealing they could be for dark matter studies.”

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