Data from the Gaia satellite show that the solar neighbourhood of the Milky Way ’ s stellar halo is imprinted with substructure from several accretion events .
Evidence of these events is found in “ the Shards ” , stars clustering with high significance in both action space and metallicity .
Stars in the Shards share a common origin , likely as ancient satellite galaxies of the Milky Way , so will be embedded in dark matter ( DM ) counterparts .
These “ Dark Shards ” contain two substantial streams ( S1 and S2 ) , as well as several retrograde , prograde and lower energy objects .
The retrograde stream S1 has a very high Earth-frame speed of \sim 550 \textrm { km s } ^ { -1 } while S2 moves on a prograde , but highly polar orbit and enhances peak of the speed distribution at around 300 \textrm { km s } ^ { -1 } .
The presence of the Dark Shards locally leads to modifications of many to the fundamental properties of experimental DM signals .
The S2 stream in particular gives rise to an array of effects in searches for axions and in the time dependence of nuclear recoils : shifting the peak day , inducing non-sinusoidal distortions , and increasing the importance of the gravitational focusing of DM by the Sun .
Dark Shards additionally bring new features for directional signals , while also enhancing the DM flux towards Cygnus .