I now believe that it could perhaps be a medieval plateau disc brooch in the shape of a star, 11th century. The type of decoration in particular looks very medieval and resembles the decorative technique on knife sheath fittings. The soldered (and broken) needle holders on the back are also typically medieval. Stefan Hesse (2015, 148, Fig. 7.7) has published a comparable, albeit five-pointed star brooch from the deserted village of "Altes Dorf" near Hellwege.