Star Stream Folding by Dark Galactic Sub-Halos

Understand

Star streams in galactic halos are long, thin, unbound structures that will be disturbed by the thousands dark matter sub-halos that are predicted to be orbiting within the main halo.

• A sub-halo generally induces a localized wave in the stream which often evolves into a "z-fold" as an initially trailing innermost part rotates faster than an initially leading outermost part.
• The folding, which becomes increasingly complex with time, leads to an apparent velocity dispersion increase and thickening of the stream.
• We measure the equivalent velocity dispersion around the local mean in the simulations, finding that it rises to about 10 km/s after 5 Gyr and 20 km/s after 13 Gyr.