Abstract
The formation of planets around binary stars may be more difficult than around single stars1,2,3. In a close binary star (with a separation of less than a hundred astronomical units), theory predicts the presence of circumstellar disks around each star, and an outer circumbinary disk surrounding a gravitationally cleared inner cavity around the stars4,5. Given that the inner disks are depleted by accretion onto the stars on timescales of a few thousand years, any replenishing material must be transferred from the outer reservoir to fuel planet formation (which occurs on timescales of about one million years). Gas flowing through disk cavities has been detected in single star systems6. A circumbinary disk was discovered around the young low-mass binary system GG Tau A (ref. 7), which has recently been shown to be a hierarchical triple system8. It has one large inner disk9 around the single star, GG Tau Aa, and shows small amounts of shocked hydrogen gas residing within the central cavity10, but other than a single weak detection11, the distribution of cold gas in this cavity or in any other binary or multiple star system has not hitherto been determined. Here we report imaging of gas fragments emitting radiation characteristic of carbon monoxide within the GG Tau A cavity. From the kinematics we conclude that the flow appears capable of sustaining the inner disk (around GG Tau Aa) beyond the accretion lifetime, leaving time for planet formation to occur there. These results show the complexity of planet formation around multiple stars and confirm the general picture predicted by numerical simulations.
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Acknowledgements
ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). A.D. thanks the French programmes PNP, PCMI, PNPS and ASA for providing funding for this study.
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A.D. led the project and participated in data reduction. All authors contributed to the data analysis, discussed the results and commented on the manuscript.
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This paper makes use of the following ALMA data: ADS/JAO.ALMA2011.0.00059.
Extended data figures and tables
Extended Data Figure 1 ALMA CO J = 6–5 velocity channel map.
For each spectroscopic channel, the velocity is given at top left. a, Full map; b, inner zoom. The beam size is 0.29″ × 0.25″ at PA 68°. The level step is 100 mJy per beam or 3.51 K corresponding to 3.4σ.
Extended Data Figure 2 IRAM CO J = 2–1 velocity channel map.
For each spectroscopic channel, the velocity is given at top left. a, Full map; b, inner zoom. The beam size is 0.68″ × 0.31″ at PA 21°. The level step is 50 mJy per beam or 5.48 K corresponding to 3.85σ.
Extended Data Figure 3 Montage of the CO J = 6–5 data.
False colours and black contours show the integrated area. The velocity gradient is given in thick contours: blue (gas approaching), black (systemic velocity) and red (gas receding). Stars show the location of Aa (south) and Ab (north). The two large ellipses show the ring edges. The three spectra sets (y axis, intensity in units of Jy per beam; x axis, velocity in units of km s−1) show the velocity gradient along the northern/southern CO J = 6–5 clump, respectively (dominated by rotation). On spectra, the red line is the systemic velocity (6.4 km s−1). From east to west, the black contours correspond to velocity contours of 6.0, 6.4 and 6.8 km s−1. The systemic velocity contour passes between the two stars (barycentre). The single spectrum corresponds to the location of the hotspot.
Extended Data Figure 4 Dust ring best model.
a, ALMA continuum data at 0.45 mm (emission from Aa circumstellar disk has been removed). b, Best model at 0.45 mm, same contour levels. c, Difference between the observations and the best model, contour levels correspond to 2σ. d, e, f, As a, b, c but for the IRAM continuum data at 1.3 mm.
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Dutrey, A., Di Folco, E., Guilloteau, S. et al. Possible planet formation in the young, low-mass, multiple stellar system GG Tau A. Nature 514, 600–602 (2014). https://doi.org/10.1038/nature13822
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DOI: https://doi.org/10.1038/nature13822
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