USC Research Team Unveils Milky Way Twins to Illuminate Dark Matter Mysteries

A research team led by the University of Southern California (USC) has made significant strides in the study of dark matter by creating supercomputer-simulated twins of our Milky Way galaxy. This groundbreaking work, which could provide new insights into one of the universe's most profound mysteries, was detailed in a trio of studies published on June 16, 2025, in *The Astrophysical Journal*, a respected publication of the American Astronomical Society.

The team, headed by Vera Gluscevic, an associate professor at USC Dornsife College of Letters, Arts, and Sciences, alongside Ethan Nadler, now an assistant professor at the University of California, San Diego, and Andrew Benson, a staff scientist at Carnegie Observatories, has dubbed their simulation project "COZMIC"—short for "Cosmological Zoom-in Simulations with Initial Conditions beyond Cold Dark Matter." This innovative approach enables researchers to explore the interactions between dark matter and regular matter in unprecedented detail.

Dark matter, an invisible substance that constitutes approximately 85% of all matter in the universe, has been a subject of intense scrutiny since it was first hypothesized in the early 20th century. Its elusive nature makes it difficult to study directly, as it does not emit light or energy. Instead, scientists infer its existence through its gravitational effects on visible matter, such as galaxies. The COZMIC simulations mark a pivotal advancement in understanding how dark matter influences galaxy formation and evolution.

According to Gluscevic, "With COZMIC, for the first time, we're able to simulate galaxies like our own under radically different physical laws—and test those laws against real astronomical observations." This capability allows researchers to measure dark matter's mass and other quantum properties, as well as its interactions with normal matter.

The simulations conducted by the COZMIC team incorporated various dark matter behavior scenarios, including:

1. **Billiard-Ball Model**: Where dark matter particles collide with protons early in the universe, smoothing out small-scale structures and potentially eliminating satellite galaxies from the Milky Way.

2. **Mixed-Sector Model**: A hybrid scenario where some dark matter particles interact with normal matter while others pass through it without interaction.

3. **Self-Interacting Model**: This scenario simulates dark matter interacting with itself both at the universe's inception and in contemporary times, thereby modifying galaxy formation across cosmic history.

Nadler noted, "Our simulations reveal that observations of the smallest galaxies can be used to distinguish dark matter models." This insight could be crucial for understanding the fundamental nature of dark matter and its role in the cosmos.

The research team also includes significant contributors such as Hai-Bo Yu from UC Riverside, Daneng Yang of Purple Mountain Observatory CAS, Xiaolong Du from UCLA, and Rui An, formerly of USC. Their collective efforts underscore the importance of collaboration in tackling complex scientific questions.

As scientists have known about dark matter's existence for decades, the challenge has been to study it in a detailed manner. The COZMIC simulations provide a new avenue for astronomers to analyze how galaxies form under varying conditions dictated by different dark matter theories. By comparing their simulated galaxies with real observational data from telescopes, the COZMIC team hopes to refine their models and gain a clearer understanding of dark matter.

The implications of this research extend beyond theoretical physics; they could reshape the foundational concepts of cosmology and our understanding of the universe. The COZMIC team intends to further their research by directly testing predictions from their simulations against actual galaxy data, aiming to uncover signatures of dark matter behavior in real cosmological structures.

In conclusion, the COZMIC project represents a significant advancement in astrophysics, pushing the boundaries of our knowledge of dark matter and potentially illuminating the mysteries of the universe. As the team continues their work, the scientific community awaits further developments that may bring us closer to understanding one of the most enigmatic components of our cosmos.