Letter | Published:

A warped disk around an infant protostar

Abstract

Recent exoplanet studies have revealed that the orbital planes of planets are not always aligned with one another or with the equatorial plane of the central star. The misalignment has been ascribed to gravitational scattering by giant planets and/or companion stars1,2,3 or to fly-bys in stellar cluster environments4. Alternatively, the misalignment could be natal: that is, such planets were born in a warped protostellar disk5,6. Warped disk structures have been reported in some transition disks and protoplanetary disks7,8, but not in the earlier stages of protostar evolution, although such a possibility is suggested by outflow morphology9,10. Here we report millimetre-wavelength dust continuum observations of the young embedded protostar IRAS 04368+2557 in the protostellar core L1527 at a distance11 of 137 parsecs; the protostar’s disk is almost edge-on12,13,14,15,16. The inner and outer parts of the disk have slightly different orbital planes, connected at 40 to 60 astronomical units from the star, but the disk has point symmetry with respect to the position of the protostar. We interpret it as a warped disk that is rotationally supported. Because there is no evidence for a companion source17,18, the warped structure must be due to either anisotropic accretion of gas with different rotational axes, or misalignment of the rotation axis of the disk with the magnetic field direction.

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Data availability

This work used the following ALMA data whose codes are ADS/JAO.ALMA #2013.0.00858.S and ADS/JAO.ALMA #2013.1.01086.S for the 0.9-mm and 1.3-mm observations, respectively. The data are available at https://almascience.nao.ac.jp/aq by setting the observation codes. The data sets generated or analysed during this study are available from the corresponding author on reasonable request.

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Acknowledgements

We thank Y. Suto, C. Chandler, Y. Aikawa, C. Ceccarelli and B. Lefloch for valuable discussions. This Letter makes use of ALMA data. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC 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. This work was supported by JSPS KAKENHI grants 25108005, 16H03964 and 18H05222.

Reviewer information

Nature thanks C. Codella and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Author information

N.S. led the project and conducted data reduction. T.H. contributed data analysis and interpretation from the theoretical point of view. Y.Z., A.H. and S.O. contributed to data analysis and simulations. All the authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing interests.

Correspondence to Nami Sakai.

Extended data figures and tables

  1. Extended Data Fig. 1 Asymmetry of the disk.

    a, b, Degree of asymmetry with respect to 180° rotation around the disk centre (‘Point symmetry’; a) and that with respect to reflection in the plane perpendicular to the disk mid-plane (‘Reflection symmetry’; b). The colour (see scale at right) denotes [I(x,y) − I(−x,−y)]/I(x,y) and [I(x,y) − I(x,−y)]/I(x,y) in a and b, respectively, where I(x,y) denotes the intensity at position (x,y). Here the Cartesian coordinates x and y are set along the disk minor and major axes, respectively.

  2. Extended Data Fig. 2 Testing possible contributions of artefacts to the observed peak offset.

    a, b, The disk model with warp (a) and without warp (b). The intensity scale is arbitrary. The nth contour represents 50 × 2n% (n = −5, −4, −3, −2, −1, 0). c, d, Results of pseudo-observations of the disk models with warp (c) and without warp (d) using the same u,v-pattern as in the actual observation; the images are obtained by tapering the u,v data to give a round-shaped beam. The nth contour represents 20 × 2nσ (n = 0, 1, …), where 1σ means 0.12 mJy per beam. e, f, Pseudo-observations of the disk models with warp (e) and without warp (f) by using the same u,v-pattern in the actual observation. The nth contour represents 20 × 2nσ (n = 0, 1, …), where 1σ means 0.09 mJy per beam. In cf, the total flux within the 20σ contour is scaled to the flux within the same region of the observed 0.9-mm dust continuum emission. See Methods section ‘Effect of the limited distribution of the u,v data’ for further details.

  3. Extended Data Fig. 3 Testing possible contributions of artefacts to the observed peak offset and to the orbital plane angle.

    a, Intensity peak offset (top graph) and orbital plane angle (bottom graph) at each radial distance derived from the observed 0.9-mm image (filled circles) and that derived from the model (solid lines) using the original synthesized beam. b, As a but with the original beam and the tapered round-beam to show the effect of beam elongation. c, Intensity peak offset and orbital plane angle at each radial distance derived from the pseudo-observations of the disk model with warp (open circles) and without warp (crosses) for the tapered round-beam case. d, As c but for the original synthesized-beam (elongated beam) case. In ad, the grey error bars represent 3σ Gaussian fitting errors.

  4. Extended Data Fig. 4 Disk width calculated from a Gaussian fit of the intensity profile at each radius.

    Values are shown for the 0.9-mm and 1.3-mm observations (filled and open symbols, respectively). Grey error bars represent 3σ Gaussian fitting errors. Solid and dashed crosses at lower left represent the synthesized beam sizes for the 0.9-mm and 1.3-mm observations, respectively.

  5. Extended Data Fig. 5 Cross-sectional views of the dust continuum emission.

    a, b, Calculated results (‘CALC’ maps) for the 0.9-mm and 1.3-mm dust continuum emission, respectively (see Methods). The nth contour represents 10 × 100.25nσ (n = 0, 1, ...), where 1σ is 0.001 mJy per beam.

  6. Extended Data Fig. 6 Disk width calculated from the CALC maps.

    Values are shown for the 0.9-mm and 1.3-mm observations (filled and open symbols, respectively). Grey error bars represent 3σ Gaussian fitting errors (see Methods for details).

  7. Extended Data Fig. 7 Peak intensities along the mid-plane.

    a, b, Results for the 0.9-mm and 1.3-mm dust continuum emission, respectively. These are obtained by the Gaussian fit of the intensity profile along the line perpendicular to the averaged disk plane. The solid and dashed grey lines represent exponential approximations of the outer and inner parts of the disk, respectively. The outer and inner parts are divided at the knee point, which is indicated by grey dashed arrows.

  8. Extended Data Fig. 8 Spiral arm model.

    a, Top view of the spiral arm model. b, Integrated density distribution along the y axis of the model. Here the inclination angle is set to be 5° (ref. 16). The intensity scale is arbitrary. The contour level x represents 10x times the peak surface density. See Methods for details.

  9. Extended Data Fig. 9 The peak positions of the integrated density distribution along the y axis of the spiral model as a function of the radial distance.

    Black lines represent the result for the spiral arm model, which are compared with the observed offsets (blue and red points show results for the north and south parts, respectively, of the disk seen in 0.9-mm dust continuum emission).

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Fig. 1: ALMA views of IRAS 04368+2557 in dust continuum emission.
Fig. 2: Radial dependence of the peak offset from the averaged disk plane.
Fig. 3: The radial dependence of the β index derived from dust continuum emission at wavelengths of 0.9 mm and 1.3 mm.
Fig. 4: A model of the infant-disk system around IRAS 04368+2557.
Extended Data Fig. 1: Asymmetry of the disk.
Extended Data Fig. 2: Testing possible contributions of artefacts to the observed peak offset.
Extended Data Fig. 3: Testing possible contributions of artefacts to the observed peak offset and to the orbital plane angle.
Extended Data Fig. 4: Disk width calculated from a Gaussian fit of the intensity profile at each radius.
Extended Data Fig. 5: Cross-sectional views of the dust continuum emission.
Extended Data Fig. 6: Disk width calculated from the CALC maps.
Extended Data Fig. 7: Peak intensities along the mid-plane.
Extended Data Fig. 8: Spiral arm model.
Extended Data Fig. 9: The peak positions of the integrated density distribution along the y axis of the spiral model as a function of the radial distance.

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