An ancient double degenerate merger in the Milky Way halo

We present an analysis and re-appraisal of the massive, carbon-enriched (DQ) white dwarf (WD) LP 93-21. Its high mass (approximate to 1.1 M-circle dot) and membership to the class of warm DQ WDs, combined with its peculiar halo kinematics suggest that this object is the product of an ancient stellar merger event, most likely that of two WDs. Furthermore, the kinematics places this object on a highly retrograde orbit driven by the accretion of a dwarf galaxy on to the Milky Way that occurred at a redshift greater than 1.5. As the product of a stellar merger LP 93-21 is probably representative of the whole class of warm/hot DQ WDs.