The Epoch of Planet Formation, Unprecedented Views of the Birth of Planets

An Astronomical Unit is the average distance of the Earth to the Sun – about 150 million kilometers, which is a useful scale for measuring distances on the scale of star systems). Using these observations, the researchers were able to image an entire population of nearby protoplanetary disks and study their AU-scale features.

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The researchers found that many substructures – concentric gaps, narrow rings – are common to nearly all the disks, while large-scale spiral patterns and arc-like features are also present in some of the cases. Also, the disks and gaps are present at a wide range of distances from their host stars, from a few AU to more than 100 AU, which is more than three times the distance of Neptune from our Sun.

These features, which could be the imprint of large planets, may explain how rocky Earth-like planets are able to form and grow. For decades, astronomers have puzzled over a major hurdle in planet-formation theory: Once dusty bodies grow to a certain size – about one centimeter in diameter – the dynamics of a smooth protoplanetary disk would induce them to fall in on their host star, never acquiring the mass necessary to form planets like Mars, Venus, and Earth.

The dense rings of dust we now see with ALMA would produce a safe haven for rocky worlds to fully mature. Their higher densities and the concentration of dust particles would create perturbations in the disk, forming zones where planetesimals would have more time to grow into fully fledged planets.

Labeled version of four of the twenty disks that comprise ALMA’s highest resolution survey of nearby protoplanetary disks. – AS 209 is a star hosting a disk that is 1 million years old and located about 400 light-years from Earth. The ALMA image shows a tightly packed series of dusty rings in its inner disk and two additional thin bands of dust very far from the central star. – HD 143006 is about 5 million years old and resides 540 light-years from Earth. This star hosts a disk that shows wide gaps between dusty lanes that demarcate the inner and outer portions of the disk. A dense arc-shaped region, possibly heralding a concentration of material where comets or other icy bodies are forming, can be seen on the lower left portion of the outer ring. – ALMA reveals sweeping spiral arms in the dust disk orbiting IM Lup, a young star located about 515 light-years from Earth. These patterns may be the result of an unseen planetary companion perturbing the disk, or a global instability in the disk structure similar to those seen in spiral galaxies like the Milky Way. – AS 205 is a multiple star system, with each star sporting its own dusty disk. Since most stars in the Milky Way are multiples, this observation provides clues to the potential for planets in such systems. This system is located about 420 light-years from Earth.

Credit: ALMA (ESO/NAOJ/NRAO) S. Andrews et al.; NRAO/AUI/NSF, S. Dagnello

“When ALMA truly revealed its capabilities with its iconic image of HL Tau, we had to wonder if that was an outlier since the disk was comparatively massive and young,” noted Laura Perez with the University of Chile and a member of the research team. “These latest observations show that, though striking, HL Tau is far from unusual and may actually represent the normal evolution of planets around young stars.”

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Contacts and sources:
Charles Blue
National Radio Astronomy Observatory

Citation:

This research is presented in the following papers accepted to the Astrophysical Journal Letters.
“The Disk Substructures at High Angular Resolution Project (DSHARP): I. Motivation, Sample, Calibration, and Overview: S. Andrews, et al. [https://arxiv.org/abs/1812.04040]
“The Disk Substructures at High Angular Resolution Project (DSHARP): II. Characteristics of Annular Substructures,” J. Huang, et al. [https://arxiv.org/abs/1812.04041]
“The Disk Substructures at High Angular Resolution Project (DSHARP): III. Spiral Structures in the Millimeter Continuum of the Elias 27, IM Lup, and WaOph 6 Disks,” J. Huang, et al. [https://arxiv.org/abs/1812.04193]
“The Disk Substructures at High Angular Resolution Project (DSHARP): IV. Characterizing Substructures and Interactions in Disks around Multiple Star Systems,” N. Kurtovic, et al. [https://arxiv.org/abs/1812.04536]
“The Disk Substructures at High Angular Resolution Project (DSHARP): V. Interpreting ALMA Maps of Protoplanetary Disks in Terms of a Dust Model” T. Birnstiel, et al. [https://arxiv.org/abs/1812.04043]
“The Disk Substructures at High Angular Resolution Project (DSHARP): VI. Dust Trapping in Thin-Ringed Protoplanetary Disks,” C. Dullemond, et al. [https://arxiv.org/abs/1812.04044]
“The Disk Substructures at High Angular Resolution Project (DSHARP): VII. The Planet-Disk Interactions Interpretation” S. Zhang, et al. [https://arxiv.org/abs/1812.04045]
“The Disk Substructures at High Angular Resolution Project (DSHARP): VIII. The Rich Ringed Substructures in the AS 209 Disk,” V, Guzmán, et al. [https://arxiv.org/abs/1812.04046]
“The Disk Substructures at High Angular Resolution Project (DSHARP): IX. A High Definition Study of the HD 163296 Planet Forming Disk” A. Isella, et al. [https://arxiv.org/abs/1812.04047]
“The Disk Substructures at High Angular Resolution Project (DSHARP): X. Multiple Rings, a Misaligned Inner Disk, and a Bright Arc in the Disk around the T Tauri Star HD 143006,” L. Pérez, et al. [https://arxiv.org/abs/1812.04049]