2/2 The white dwarf is stealing material from a companion star. In other binary systems, this material forms a disc around the dwarf, and winds blowing out from the disc can create a bow shock. But this system has no signs of a disc. The white dwarf has a strong magnetic field, but it can only power the bow shock for a few hundred years. The shape and size of the shock indicates it's been there for more than 1000 years, so we are still missing some hidden energy source.