An official website of the United States government
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.
more »
« less
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.
more »
« less
- Award ID(s):
- 2009842
- 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
More Like this
-
-
Aims. We present high-sensitivity and high spectral-resolution NOEMA observations of the Class 0/I binary system SVS13A, composed of the low-mass protostars VLA4A and VLA4B, with a separation of ~90 au. VLA4A is undergoing an accretion burst that is enriching the chemistry of the surrounding gas, which provides an excellent opportunity to probe the chemical and physical conditions as well as the accretion process. Methods. We observe the (12 K –11 K ) lines of CH 3 CN and CH 3 13 CN, the DCN (3–2) line, and the C 18 O (2–1) line toward SVS13A using NOEMA. Results. We find complex line profiles at disk scales that cannot be explained by a single component or pure Keplerian motion. By adopting two velocity components to model the complex line profiles, we find that the temperatures and densities are significantly different among these two components. This suggests that the physical conditions of the emitting gas traced via CH 3 CN can change dramatically within the circumbinary disk. In addition, combining our observations of DCN (3–2) with previous ALMA observations at high angular resolution, we find that the binary system (or VLA4A) might be fed by an infalling streamer from envelope scales (~700 au). If this is the case, this streamer contributes to the accretion of material onto the system at a rate of at least 1.4 × 10 −6 M ⊙ yr −1 . Conclusions. We conclude that the CH 3 CN emission in SVS13A traces hot gas from a complex structure. This complexity might be affected by a streamer that is possibly infalling and funneling material into the central region.more » « less
-
Abstract We present a detailed study of the massive star-forming region G35.2-0.74N with Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm multi-configuration observations. At 0.″2 (440 au) resolution, the continuum emission reveals several dense cores along a filamentary structure, consistent with previous ALMA 0.85 mm observations. At 0.″03 (66 au) resolution, we detect 22 compact sources, most of which are associated with the filament. Four of the sources are associated with compact centimeter continuum emission, and two of these are associated with H30αrecombination line emission. The H30αline kinematics shows the ordered motion of the ionized gas, consistent with disk rotation and/or outflow expansion. We construct models of photoionized regions to simultaneously fit the multiwavelength free–free fluxes and the H30αtotal fluxes. The derived properties suggest the presence of at least three massive young stars with nascent hypercompact Hiiregions. Two of these ionized regions are surrounded by a large rotating structure that feeds two individual disks, revealed by dense gas tracers, such as SO2, H2CO, and CH3OH. In particular, the SO2emission highlights two spiral structures in one of the disks and probes the faster-rotating inner disks. The12CO emission from the general region reveals a complex outflow structure, with at least four outflows identified. The remaining 18 compact sources are expected to be associated with lower-mass protostars forming in the vicinity of the massive stars. We find potential evidence for disk disruption due to dynamic interactions in the inner region of this protocluster. The spatial distribution of the sources suggests a smooth overall radial density gradient without subclustering, but with tentative evidence of primordial mass segregation.more » « less
-
Abstract Protostellar disks are an ubiquitous part of the star formation process and the future sites of planet formation. As part of the Early Planet Formation in Embedded Disks large program, we present high angular resolution dust continuum (∼40 mas) and molecular line (∼150 mas) observations of the Class 0 protostar IRAS 15398–3359. The dust continuum is small, compact, and centrally peaked, while more extended dust structures are found in the outflow directions. We perform a 2D Gaussian fitting and find the deconvolved size and 2σradius of the dust disk to be 4.5 × 2.8 au and 3.8 au, respectively. We estimate the gas+dust disk mass assuming optically thin continuum emission to be 0.6MJ–1.8MJ, indicating a very low mass disk. The CO isotopologues trace components of the outflows and inner envelope, while SO traces a compact, rotating disk-like component. Using several rotation curve fittings on the position–velocity diagram of the SO emission, the lower limits of the protostellar mass and gas disk radius are 0.022M⊙and 31.2 au, respectively, from our Modified 2 single power-law fitting. A conservative upper limit of the protostellar mass is inferred to be 0.1M⊙. The protostellar mass accretion rate and the specific angular momentum at the protostellar disk edge are found to be in the range of (1.3–6.1) × 10−6M⊙yr−1and (1.2–3.8) × 10−4km s−1pc, respectively, with an age estimated between 0.4 × 104yr and 7.5 × 104yr. At this young age with no clear substructures in the disk, planet formation would likely not yet have started. This study highlights the importance of high-resolution observations and systematic fitting procedures when deriving dynamical properties of deeply embedded Class 0 protostars.more » « less
-
Abstract We present our investigation of the extended ultraviolet (XUV) disk galaxy, NGC 3344, conducted as part of Deciphering the Interplay between the Interstellar medium, Stars, and the Circumgalactic medium survey. We use surface and aperture photometry of individual young stellar complexes to study star formation and its effect on the physical properties of the interstellar medium. We measure the specific star formation rate (sSFR) and find it to increase from 10 −10 yr −1 in the inner disk to >10 −8 yr −1 in the extended disk. This provides evidence for inside-out disk growth. If these sSFRs are maintained, the XUV disk stellar mass can double in ∼0.5 Gyr, suggesting a burst of star formation. The XUV disk will continue forming stars for a long time due to the high gas depletion times ( τ dep ). The stellar complexes in the XUV disk have high-Σ H I and low-Σ SFR with τ dep ∼ 10 Gyr, marking the onset of a deviation from the traditional Kennicutt–Schmidt law. We find that both far-ultraviolet (FUV) and a combination of FUV and 24 μ m effectively trace star formation in the XUV disk. H α is weaker in general and prone to stochasticities in the formation of massive stars. Investigation of the circumgalactic medium at 29.5 kpc resulted in the detection of two absorbing systems with metal-line species: the stronger absorption component is consistent with gas flows around the disk, most likely tracing inflow, while the weaker component is likely tracing corotating circumgalactic gas.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1051/0004-6361/202040000
