Nearly all young stars are initially surrounded by ‘protoplanetary’ disks of gas and dust, and in the case of single stars at least 30% of these disks go on to form planets1. The process of protoplanetary disk formation can result in initial misalignments, where the disk orbital plane is different from the stellar equator in single-star systems, or different from the binary orbital plane in systems with two stars2. A quirk of the dynamics means that initially misaligned ‘circumbinary’ disks—those that surround two stars—are predicted to evolve to one of two possible stable configurations: one where the disk and binary orbital planes are coplanar and one where they are perpendicular (a ‘polar’ configuration)3,4,5. Previous work has found coplanar circumbinary disks6, but no polar examples were known until now. Here, we report the first discovery of a protoplanetary circumbinary disk in the polar configuration, supporting the predictions that such disks should exist. The disk shows some characteristics that are similar to disks around single stars, and that are attributed to dust growth. Thus, the first stages of planet formation appear able to proceed in polar circumbinary disks.
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The ALMA data used in this study are available in the ALMA Science Archive (project code 2017.1.00350.S). Post-processing, modelling and other code used in this study are available on GitHub at https://github.com/drgmk/hd98800_alma_c5. Post-processed data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
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G.M.K. is supported by the Royal Society as a Royal Society University Research Fellow. L.M. acknowledges support from the Smithsonian Institution as a Submillimeter Array Fellow. O.P. is supported by the Royal Society Dorothy Hodgkin Fellowship. S.F. acknowledges an ESO Fellowship. We thank A. Ribas for sharing the Very Large Array image of HD 98800. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2017.1.00350.S. ALMA is a partnership of the ESO (representing its member states), NSF (United States) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ.
Supplementary text, Supplementary references, Supplementary Tables 1–3, Supplementary Figures 1–7