Recent findings published in The Astrophysical Journal Letters enhance our understanding of dark matter, which is believed to constitute 85% of the universe's matter. Stellar streams, groups of stars moving along a common trajectory, are significantly affected by dark matter, making them essential for studying this elusive substance. Characteristics such as gaps and spurs within these streams provide vital insights into the distribution and behavior of dark matter within galaxies.
The Milky Way's galactic halo, a spherical region extending beyond the galaxy's visible edge, contains both dark matter and known stellar streams. Researchers have identified that the spur and gap features in the GD-1 stellar stream cannot be solely attributed to gravitational influences from globular clusters or satellite galaxies. Instead, these anomalies suggest the presence of an unidentified perturbing object—a dense subhalo.
Professor Yu, a physicist and astronomer, noted, "CDM subhalos typically lack the density needed to produce the distinctive features observed in the GD-1 stream. However, our research demonstrates that a collapsing SIDM subhalo could achieve the necessary density. Such a compact subhalo would exert the gravitational influence required to account for the observed perturbations in the GD-1 stream."
Unlike traditional cold dark matter (CDM), which assumes dark matter particles do not interact, self-interacting dark matter (SIDM) theories propose that these particles can interact through a new dark force. To validate their hypothesis, Yu's team utilized advanced N-body simulations to model the behavior of a collapsing SIDM subhalo.
Yu stated, "Our findings provide a new explanation for the spur and gap features in GD-1, previously thought to indicate a close encounter with a dense object. In our scenario, the perturber is the SIDM subhalo, disrupting the spatial and velocity distributions of stars in the stream, leading to the distinctive features we observe in the GD-1 stellar stream."
This research not only illuminates the properties of dark matter but also underscores the potential of stellar streams as a method for investigating galactic dynamics. Yu added, "This work opens a promising new avenue for exploring the self-interacting properties of dark matter through stellar streams. It marks an exciting step forward in our understanding of dark matter and the dynamics of the Milky Way."
The research received support from the U.S. Department of Energy and the John Templeton Foundation. Collaborators included Xingyu Zhang and Daneng Yang from UC Riverside, and Ethan O. Nadler from UC San Diego.