Abstract Giant planets have been discovered at large separations from the central star. Moreover, a striking number of young circumstellar disks have gas and/or dust gaps at large orbital separations, potentially driven by embedded planetary objects. To form massive planets at large orbital separations through core accretion within the disk lifetime, however, an early solid body to seed pebble and gas accretion is desirable. Young protoplanetary disks are likely self-gravitating, and these gravitoturbulent disks may efficiently concentrate solid material at the midplane driven by spiral waves. We run 3D local hydrodynamical simulations of gravitoturbulent disks with Lagrangian dust particles to determine whether particle and gas self-gravity can lead to the formation of dense solid bodies, seeding later planet formation. When self-gravity between dust particles is included, solids of size St = 0.1–1 concentrate within the gravitoturbulent spiral features and collapse under their own self-gravity into dense clumps up to several M ⊕ in mass at wide orbits. Simulations with dust that drift most efficiently, St = 1, form the most massive clouds of particles, while simulations with smaller dust particles, St = 0.1, have clumps with masses an order of magnitude lower. When the effect of dust backreaction onto the gas is included, dust clumps become smaller by a factor of a few but more numerous. The existence of large solid bodies at an early stage of the disk can accelerate the planet formation process, particularly at wide orbital separations, and potentially explain planets distant from the central stars and young protoplanetary disks with substructures.
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Physical conditions in the warped accretion disk of a massive star: 349 GHz ALMA observations of G023.01−00.41
Young massive stars warm up the large amount of gas and dust that condenses in their vicinity, exciting a forest of lines from different molecular species. Their line brightness is a diagnostic tool of the gas’s physical conditions locally, which we use to set constraints on the environment where massive stars form. We made use of the Atacama Large Millimeter/submillimeter Array at frequencies near 349 GHz, with an angular resolution of 0′′.1, to observe the methyl cyanide (CH 3 CN) emission which arises from the accretion disk of a young massive star. We sample the disk midplane with twelve distinct beams, where we get an independent measure of the gas’s (and dust’s) physical conditions. The accretion disk extends above the midplane, showing a double-armed spiral morphology projected onto the plane of the sky, which we sample with ten additional beams: Along these apparent spiral features, gas undergoes velocity gradients of about 1 km s −1 per 2000 au. The gas temperature ( T ) rises symmetrically along each side of the disk, from about 98 K at 3000 au to 289 K at 250 au, following a power law with radius R −0.43 . The CH 3 CN column density ( N ) increases from 9.2 × 10 15 cm −2 to 8.7 × 10 17 cm −2 at the same radii, following a power law with radius R −1.8 . In the framework of a circular gaseous disk observed approximately edge-on, we infer an H 2 volume density in excess of 4.8 ×10 9 cm −3 at a distance of 250 au from the star. We study the disk stability against fragmentation following the methodology by Kratter et al. (2010, ApJ, 708, 1585), which is appropriate under rapid accretion, and we show that the disk is marginally prone to fragmentation along its whole extent.
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- Award ID(s):
- 2009842
- NSF-PAR ID:
- 10347673
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 655
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A72
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract We present Atacama Large Millimeter/submillimeter Array observations with a 800 au resolution and radiative-transfer modeling of the inner part (
r ≈ 6000 au) of the ionized accretion flow around a compact star cluster in formation at the center of the luminous ultracompact Hii region G10.6-0.4. We modeled the flow with an ionized Keplerian disk with and without radial motions in its outer part, or with an external Ulrich envelope. The Markov Chain Monte Carlo fits to the data give total stellar massesM ⋆from 120 to 200M ⊙, with much smaller ionized-gas massesM ion-gas= 0.2–0.25M ⊙. The stellar mass is distributed within the gravitational radiusR g ≈ 1000 to 1500 au, where the ionized gas is bound. The viewing inclination angle from the face-on orientation isi = 49°–56°. Radial motions at radiir >R g converge tov r ,0≈ 8.7 km s−1, or about the speed of sound of ionized gas, indicating that this gas is marginally unbound at most. From additional constraints on the ionizing-photon rate and far-IR luminosity of the region, we conclude that the stellar cluster consists of a few massive stars withM star= 32–60M ⊙, or one star in this range of masses accompanied by a population of lower-mass stars. Any active accretion of ionized gas onto the massive (proto)stars is residual. The inferred cluster density is very large, comparable to that reported at similar scales in the Galactic center. Stellar interactions are likely to occur within the next million years. -
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ABSTRACT Young massive clusters (YMCs) are compact (≲1 pc), high-mass (>104 M⊙) stellar systems of significant scientific interest. Due to their rarity and rapid formation, we have very few examples of YMC progenitor gas clouds before star formation has begun. As a result, the initial conditions required for YMC formation are uncertain. We present high resolution (0.13 arcsec, ∼1000 au) ALMA observations and Mopra single-dish data, showing that Galactic Centre dust ridge ‘Cloud d’ (G0.412 + 0.052, mass = 7.6 × 104 M⊙, radius = 3.2 pc) has the potential to become an Arches-like YMC (104 M⊙, r ∼ 1 pc), but is not yet forming stars. This would mean it is the youngest known pre-star-forming massive cluster and therefore could be an ideal laboratory for studying the initial conditions of YMC formation. We find 96 sources in the dust continuum, with masses ≲3 M⊙ and radii of ∼103 au. The source masses and separations are more consistent with thermal rather than turbulent fragmentation. It is not possible to unambiguously determine the dynamical state of most of the sources, as the uncertainty on virial parameter estimates is large. We find evidence for large-scale (∼1 pc) converging gas flows, which could cause the cloud to grow rapidly, gaining 104 M⊙ within 105 yr. The highest density gas is found at the convergent point of the large-scale flows. We expect this cloud to form many high-mass stars, but find no high-mass starless cores. If the sources represent the initial conditions for star formation, the resulting initial mass function will be bottom heavy.
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Abstract We present 250 GHz continuum and H29α line data toward W 49 N:A2, a hypercompact H ii region ionized by an O9 star. The data obtained with ALMA at a resolution of ∼0${_{.}^{\prime\prime}}$05 (600 au) confirmed the presence of an ionized ring with a radius of ∼700 au inclined by ∼50° (0° for pole-on). It has a width of ∼1000 au and is relatively flat with a scale height of less than several hundred au. The tilted ring, or the apparent ellipse, has a prominent velocity difference between its NW and SE ridges along the minor axis, suggesting that it is expanding in the equatorial plane at a velocity of 13.2 km s−1. The ring also shows a hint of rotation at 2.7 km s−1, which is significantly (2.5 σ) smaller than the Kepler velocity of 5.2 km s−1 at its radius around the 20 M⊙ star. This can be interpreted as that the ring gas has been transported from the radius of ∼170 au by conserving its original specific angular momentum that it had there. The ionized ring may thus be a remnant of the accretion disk that fed the O9 star, the radiation or magnetic activities of which became so strong that the disk accretion was reversed due to the intense thermal or magneto-hydrodynamic pressure around the star. The data has revealed a rare example of how a massive star terminates its accretion at the end of its formation, transforming a hypercompact H ii region into an ultracompact H ii region.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1051/0004-6361/202040000
