USC hosts talk to explore the future of dark matter

With the rapid advancement of technology, there has been more anticipation for astrophysics research than ever before. Scientists and enthusiasts alike are eager to see how our understanding of the cosmos may be revolutionized in the near future.

On Sept. 29, that curiosity brought students, faculty and local researchers to USC Dornsife’s weekly Physics and Astronomy Colloquium where Dr. Ana Bonaca, a scientist at the Carnegie Observatories in Pasadena, shared a potential breakthrough.

The talk focused on dark matter, one of the most elusive and compelling subjects in modern astrophysics. 

Although it makes up roughly 85% of the universe's mass, dark matter was first identified less than a century ago. True to its name, dark matter neither emits, absorbs nor reflects light, leaving its fundamental composition, origin and full range of properties largely unknown.

Despite its mysterious nature, dark matter’s gravitational influence is evident in the rapid rotation of galaxies and in the bending of light around massive objects, a phenomenon known as gravitational lensing.

While most dark matter research tends to center around direct detection experiments or large-scale galactic models, Bonaca has devoted much of her research to a complementary approach: observing stellar streams. Stellar streams are narrow, ribbon-like trails of stars formed when small star clusters or dwarf galaxies are torn apart and stretched by the Milky Way’s gravitational forces.

Her team has been studying how subhalos, small clumps of dark matter, affect stellar streams. When a subhalo passes nearby, it tugs on the stream, creating subtle gaps or kinks. Through analyzing these distortions, scientists can infer where dark matter is concentrated — even though it emits no light. “We have seen in a number of streams perturbations that we believe are consistent with dark matter, but we are unable to guarantee it,” Bonaca noted in her presentation.

“It is not necessarily dark matter. It could be a compact object, star clusters, dwarf galaxies, spiral arms, or molecular clouds producing velocity kicks very similar to what we expect of dark matter.” However, information from both the LSST and Via Project are expected to play a critical role in helping astronomers identify the causes of stellar stream distortions and refine our understanding of the galaxy’s hidden dark matter.

“I am fully prepared for there to be surprises,” Bonaca stated. “But I thought that was really exciting… launching into this unknown.”

The next few years will be transformative for this line of research. 

Bonaca highlighted the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST)—a decade-long project that will photograph the entire southern sky. Its massive 3.2-gigapixel camera will trace millions of faint stars, mapping the Milky Way in unprecedented detail. “We’ll be able to see stars that are much fainter than what we have at the moment… basically as soon as we have the first full map of the sky from the project,” she said.

She also spotlighted the upcoming 2027 collaboration between Carnegie Observatories and the Harvard-Smithsonian Center for Astrophysics known as the Via Project. Once launched, the investigation will use twin spectrographs to conduct an all-sky survey of the Milky Way. 

For Bonaca and her colleagues, the next decade promises to be a turning point. With LSST and the Via Project set to reveal millions of faint stars and track the subtle dynamics of stellar streams, astronomers are bound to move ever closer to uncovering the true nature of dark matter.

As USC continues to host leading voices in physics and astronomy, talks like Bonaca’s give students the chance to see scientific discovery in real time. “The nice part about being in the LA area is that there's so much astronomy research,” Bonaca said. “So basically, don't feel shy to reach out to people and ask.”