One of the most extensively studied stellar streams within the galactic halo of the Milky Way is the GD-1 stellar stream.
It is known for its long, thin structure and distinctive features. It exhibits spur and gap features that have puzzled scientists for many years.
A team of researchers led by Hai-Bo Yu, a professor of physics and astronomy from the University of California, Riverside, proposed that these strange features may result from a core-collapsing self-interacting dark matter (SIDM) subhalo, a smaller and denser satellite halo within the galactic halo.
The findings could have significant implications for our understanding of dark matter, a mysterious and invisible component that is thought to make up 85 percent of all matter in the universe. Its nature and properties are not very well understood.
Stellar streams are groups of stars that move collectively along a shared path. Their movement is influenced by dark matter, which means they can be used to trace dark matter throughout a galaxy.
Features such as gaps and spurs within a stream help provide important clues. A gap is a localized under-density of stars along the stream, while a spur is an over-density of stars stretching out from the main body of the stream.
The Milky Way’s galactic halo, a roughly spherical region that extends beyond the visible edge of the galaxy, contains dark matter and known stellar streams.
Astronomers have discovered that the spur and gap features of the GD-1 stellar stream cannot be explained by the gravitational forces of globular clusters or satellite galaxies.
However, these features can be attributed to the presence of a previously unidentified perturbing object, such as a subhalo.
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But the density of the object needs to be much higher than that of traditional cold dark matter (CDM) subhalos.
“CDM subhalos typically lack the density needed to produce the distinctive features observed in the GD-1 stream,” said Yu.
“However, our research demonstrates that a collapsing SIDM subhalo could achieve the necessary density. Such a compact subhalo would be dense enough to exert the gravitational influence required to account for the observed perturbations in the GD-1 stream.”
The prevailing dark matter theory is CDM, which assumes that dark matter particles do not interact. On the other hand, SIDM theories propose that dark matter particles can interact with each other through a new dark force.
In the study, Yu and colleagues used advanced numerical simulations called N-body simulations to replicate the behavior of a collapsing SIDM subhalo.
“Our team’s findings offer a new explanation for the observed spur and gap features in GD-1, which have long been thought to indicate a close encounter with a dense object,” said Yu.
“In our scenario, the perturber is the SIDM subhalo, which disrupts the spatial and velocity distributions of the stars in the stream and creates the distinctive features we see in the GD-1 stellar stream.”
The study was published in Astrophysical Journal Letters.
