We use the SDSS- Gaia catalogue to search for substructure in the stellar halo .
The sample comprises 62 133 halo stars with full phase space coordinates and extends out to heliocentric distances of \sim 10 kpc .
As actions are conserved under slow changes of the potential , they permit identification of groups of stars with a common accretion history .
We devise a method to identify halo substructures based on their clustering in action space , using metallicity as a secondary check .
This is validated against smooth models and numerical constructed stellar halos from the Aquarius simulations .
We identify 21 substructures in the SDSS- Gaia catalogue , including 7 high significance , high energy and retrograde ones .

We investigate whether the retrograde substructures may be material stripped off the atypical globular cluster \omega Centauri .
Using a simple model of the accretion of the progenitor of the \omega Centauri , we tentatively argue for the possible association of up to 5 of our new substructures ( labelled Rg1 , Rg3 , Rg4 , Rg6 and Rg7 ) with this event .
This sets a minimum mass of 5 \times 10 ^ { 8 } M _ { \odot } for the progenitor , so as to bring \omega Centauri to its current location in action – energy space .
Our proposal can be tested by high resolution spectroscopy of the candidates to look for the unusual abundance patterns possessed by \omega Centauri stars .