A self-collapsing, self-interacting dark matter subhalo is a unique spur observed in GD-1, a stellar stream within the Milky Way’s galactic halo, according to a new study led by astronomers at the University of California, Riverside, and is responsible for the gap characteristics.
GD-1 exhibits spur and gap structures that may be attributed to its proximity with a dense substructure. Image credit: University of California, Riverside.
A stellar stream is a group of stars that collectively move along a shared orbit.
A gap refers to a local under-density of stars along the stream, whereas a spur refers to an excess of star density extending outward from the main body of the stream.
Because dark matter governs the movement of star streams, astronomers can use it to track the invisible dark matter in galaxies.
The Milky Way’s halo is a roughly spherical region surrounding our galaxy that contains dark matter and extends beyond the visible edge of our galaxy.
Astronomers discovered that the fulcrum and gap features of the GD-1 star stream cannot easily be attributed to the gravitational influence of the Milky Way’s known globular clusters or satellite galaxies.
However, these features may be explained by unknown perturbing objects such as subhalos.
But the object’s density would need to be significantly higher than that predicted by conventional cold dark matter (CDM) subhalos.
“CDM subhalos typically lack the density necessary to produce the unique features observed in GD-1 streams,” said Haibo Yu, a professor at the University of California, Riverside.
“However, our study shows that a subhalo of collapsing self-interacting dark matter (SIDM) can achieve the required density.”
“Such a compact subhalo would be dense enough to exert the gravitational effects necessary to explain the observed perturbations in the GD-1 flow.”
The currently popular dark matter theory, CDM, assumes that dark matter particles have no collisions.
SIDM, a theoretical form of dark matter, proposes that dark matter particles self-interact through new dark forces.
In the study, Professor Yu and his colleagues used a numerical simulation called N-body simulation to model the behavior of a collapsing SIDM subhalo.
“Our team’s findings provide a new explanation for the lobes and gap features observed on GD-1, long thought to indicate close encounters with dense objects. ” said Professor Yu.
“In our scenario, the perturbation source is the SIDM subhalo, which perturbs the spatial and velocity distribution of stars within the star stream, producing the unique features seen in the GD-1 star stream.”
The discovery also provides insight into the nature of dark matter itself.
“This study opens a promising new avenue to study the self-interaction properties of dark matter through stellar streams,” Professor Yu said.
“This represents an exciting step forward in our understanding of dark matter and the dynamics of the Milky Way.”
The full study will appear in Astrophysics Journal Letter.
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Zhang Xingyu others. 2025. GD-1 Stellar Stream Parter Bar as a self-interacting dark matter halo with a collapsed core. APJL 978, L23; doi: 10.3847/2041-8213/ada02b
Source: www.sci.news
