def handle_collision(self, primary, secondary, stellar_evolution_code=None, gravity_code=None): primary = self.add_particle_with_internal_structure(primary, stellar_evolution_code=stellar_evolution_code) secondary = self.add_particle_with_internal_structure(secondary, stellar_evolution_code=stellar_evolution_code) merge_product = Particle( key = self.key_for_merge_product(primary, secondary), primary = primary, secondary = secondary ) return self.merge_products.add_particles(merge_product.as_set())