Exploring Dark Matter

Particle physics is a discipline within the field that studies the nature of the smallest detectable particles that make up matter and radiation. The Standard Model is the theory that explains what these particles are and how they interact with each other, and it was developed by scientists during the 1970s.

While the Standard Model explains a lot about the laws of physics, it isn’t able to explain all phenomena, which is why it can’t be considered a complete theory of fundamental interactions. For example, the Standard Model can’t account for dark matter.

“Roughly 80 percent of the matter of the universe is made up of material that we can’t directly observe and can’t be described by any particles within the framework of the Standard Model,” said Yue Zhao, assistant professor of physics, who recently joined the University of Utah in July.

“This mysterious missing component is known as dark matter, which neither interacts strongly with light nor atoms. Exploring the properties of dark matter is one of my research interests.”

Existence of Dark Matter

If we can’t actually see dark matter, how do we know it exists? Astrophysicists can calculate the mass distribution in large astrophysical systems in space such as our galaxy by studying the motion of stars. When scientists began studying spiral galaxies nearly 70 years ago, they expected to see stars near the center of a galaxy moving faster than at the outer edges. Instead, they found that stars both near the center and in outer areas traveled approximately at the same speed, which told them that galaxies contained more mass than could be seen. Additionally, massive objects in the universe bend and distort light, allowing them to act as a lens. By observing how galaxy clusters distort light, astronomers have been able to create a dark matter map in galaxy clusters.

In the Standard Model, the familiar matter of the universe is composed of protons and neutrons, called baryonic matter. Most scientists think that dark matter is composed of non-baryonic matter, but their weak interactions with normal matter make them difficult to detect.

“One of the things I love about studying dark matter is that it requires creativity,” said Zhao. “Some scientists have spent decades looking for a particular type of dark matter particle without much success. If you’re studying dark matter, you have to keep an open mind and find new methods to look for it.”

LIGO Collaboration

One method that interests Zhao is the use of a gravitational wave detector, such as the detectors used at the Laser Interferometer Gravitational- Wave Observatories (LIGO), located in Hanford, Washington, and Livingston, Louisiana. The LIGO Scientific Collaboration is a group of scientists focused on detecting gravitational waves and using them to explore the physics of gravity. The group

seeks to develop gravitational wave science as a tool to understand astronomy. “While a gravitational wave detector is designed to look for gravitational waves, it also serves as a perfect detector to help find a particular type of dark matter,” said Zhao. “We may find dark matter by using LIGO and by implementing a new data analysis strategy.”

Zhao’s love of physics began when he read A Brief History of Time: From the Big Bang to Black Holes by Stephen Hawking. “This is such a great book, and it explains so many deep and fantastic physics concepts with language that can easily be understood by a non-scientist,” said Zhao. “The laws of nature are beautifully described in the book, and I must have reread some of these sections at least five times.”

Moving to the U.S.

Although Zhao learned some physics as a child, he didn’t begin studying it formally until he was a teenager. Later, he tackled advanced physics at Peking University and moved to Rutgers University to pursue a Ph.D. “When I first arrived at Rutgers, I didn’t really have a clear idea of what I wanted to do,” said Zhao. “I started working with my thesis advisor by accident, and I was lucky that my research interests and his matched perfectly.”

As a newcomer to Utah, Zhao is impressed with its natural beauty. He likes hiking and is looking forward to visiting all of Utah’s national parks. He also wants to get better at skiing. He credits his colleagues with making him feel welcome at the U, and he’s taken advantage of the resources available on campus, especially the services for non-native speakers.

As Zhao moves forward in his research, he hopes to build his own LIGO team at the U. “Having a world- class dark matter team to collaborate with LIGO and develop new ideas would be a dream come true,” he said.