The starfish twins: Two young planetary nebulae with extreme multipolar morphology

We present N alpha images of two objects, He 2-47 and M1-37, obtained during a Hubble Space Telescope imaging survey of young planetary nebulae (PNs) selected on the basis of their low-excitation characteristics. The two objects show a highly aspherical morphology, characterized by multiple lobes distributed around the central star. Such a morphology has never been seen before in any astrophysical setting. Bright structures near the minor axes indicate the presence of dense equatorial tori (seen edge-on in M1-37 and as partial elliptical rings in He 2-47). In both nebulae, the central star is found to be offset from the geometrical center of symmetry of the waist region. The multiple lobes of He 2-47 and M1-37 have been produced fairly recently (a few hundred years ago), based on rough estimates of their expansion ages. The extreme multipolar morphology of these PNs supports the recent hypothesis of Sahai & Trauger that the primary agents for shaping PNs are high-speed collimated outflows that operate during the late asymptotic giant branch (AGE) and/or early post-AGE evolutionary phase; these outflows change their direction episodically, and/or multiple collimated outflows with different axes operate (quasi)simultaneously. Drastic modifications of existing theories or completely new ideas are needed in order to obtain a full understanding of the salient morphological features of He 2-47 and M1-37.