Turbulence in molecular clouds - A new diagnostic tool to probe their origin

Canuto, V. M.; Battaglia, A.

doi:10.1086/184523

Cited by 5 publications

(3 citation statements)

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“…where P and ρ are the gas mean pressure and density, Ω k is the Keplerian frequency, v φ is the mean relative transverse velocity between particles and gas, v r the mean relative radial velocity, V r the mean gas radial velocity (from Hughes & Armitage (2010)), t s * the stopping time of the particle, Sc the Schmidt number, D the diffusion coefficient, r the heliocentric distance and ρ d the global solid particles density. For numerical simplicity we follow Stepinski & Valageas (1996) in choosing D = 3ν, a value consistent with more detailed numerical values of D (Canuto & Battaglia 1988), and which cancels the third term in the second equation. The presence of a strong vertical magnetic field though might affect the value of D (Johansen et al 2006).…”

Section: The Evolution Of Solidsmentioning

confidence: 99%

Carbon-Rich Planet Formation in a Solar Composition Disk

Ali-Dib¹,

Mousis²,

Petit³

et al. 2014

ApJ

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The C-to-O ratio is a crucial determinant of the chemical properties of planets. The recent observation of WASP 12b, a giant planet with a C/O value larger than that estimated for its host star, poses a conundrum for understanding the origin of this elemental ratio in any given planetary system. In this paper, we propose a mechanism for enhancing the value of C/O in the disk through the transport and distribution of volatiles. We construct a model that computes the abundances of major C and O bearing volatiles under the influence of gas drag, sublimation, vapor diffusion, condensation and coagulation in a multi-iceline 1+1D protoplanetary disk. We find a gradual depletion in water and carbon monoxide vapors inside the water's iceline with carbon monoxide depleting slower than water. This effect increases the gaseous C/O and decreases the C/H ratio in this region to values similar to those found in WASP 12b's day side atmosphere. Giant planets whose envelopes were accreted inside the water's iceline should then display C/O values larger than those of their parent stars, making them members of the class of so-called "carbon-rich planets".

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Section: The Evolution Of Solidsmentioning

confidence: 99%

Carbon-Rich Planet Formation in a Solar Composition Disk

Ali-Dib¹,

Mousis²,

Petit³

et al. 2014

ApJ

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“…However, it has been demonstrated that in a standard viscously driven accretion disk, unless the ratio of magnetic diffusivity to viscosity (the inverse magnetic Prandtl number) in the disk is very small (comparable to H/R), such inward advection of field does not take place (Lubow, Papaloizou, & Pringle 1994a;Reyes-Ruiz & Stepinski 1996;Heyvaerts, Priest, & Bardou 1996). It is important to note, however, that in a disk in which the angular momentum transport is mainly due to the effects of self-sustaining hydromagnetic turbulence (Balbus & Hawley 1991;Hawley, Gammie, & Balbus 1995, 1996Stone, Hawley, Gammie & Balbus 1996;Brandenburg, Nordlund, Stein, & Torkelsson 1995), the magnetic Prandtl number is likely to be of order unity (Parker 1971;Pouquet, Frisch & Léorat 1976;Zel'dovich, Ruzmaikin, & Sokoloff 1983;Canuto & Battaglia 1988). Thus, if the disk surrounding the black hole is at any radius a standard accretion disk in which the dominant mode of angular momentum loss is by viscous transport within the disk, poloidal magnetic flux cannot be simply advected inwards from infinity.…”

Section: Advection Of Poloidal Field: Standard Accretion Diskmentioning

confidence: 99%

Extracting Energy from Black Holes: The Relative Importance of the Blandford‐Znajek Mechanism

Livio

Ogilvie

Pringle

1999

ApJ

296

367

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We critically assess the role of the Blandford-Znajek mechanism in the powering of outflows from accretion disk-fed black holes. We argue that there is no reason to suppose that the magnetic field threading the central spinning black hole differs significantly in strength from that threading the central regions of the disk. In this case, we show that the electromagnetic output from the inner disk regions is expected in general to dominate over that from the hole. Thus the spin (or not) of the hole is probably irrelevant to the expected electromagnetic power output from the system. We also point out that the strength of the poloidal field in the center of a standard accretion disk has been generally overestimated, and discuss scenarios which might give rise to more significant central poloidal fields.

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“…More detailed models of turbulent disks suggested that a large-scale, weak magnetic field such as that shown in Figure 1 in fact will diffuse outward rapidly (van Ballegooijen 1989;Lubow, Papaloizou, & Pringle 1994) if the turbulent magnetic diffusivity and turbulent viscosity are of similar order of magnitude, as they are expected to be (Parker 1971;Bisnovatyi-Kogan & Ruzmaikin 1976;Canuto & Battaglia 1988)-the turbulence responsible for driving the accretion also leads to enhanced reconnection of the large-scale radial field across the thickness of the disk, thereby causing the vertical field to diffuse away. This cast doubt on the idea that weak fields could be dragged inward and compressed by advection.…”

Section: Introductionmentioning

confidence: 99%

Advection of Magnetic Fields in Accretion Disks: Not So Difficult After All

Rothstein

Lovelace

2008

ApJ

123

122

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We show that a large-scale, weak magnetic field threading a turbulent accretion disk tends to be advected inward, contrary to previous suggestions that it will be stopped by outward diffusion. The efficient inward transport is a consequence of the diffuse, magnetically dominated surface layers of the disk, where the turbulence is suppressed and the conductivity is very high. This structure arises naturally in three-dimensional simulations of magnetorotationally unstable disks, and we demonstrate here that it can easily support inward advection and compression of a weak field. The advected field is anchored in the surface layer but penetrates the main body of the disk, where it can generate strong turbulence and produce values of (i.e., the turbulent stress) that are large enough to match observational constraints; typical values of the vertical magnetic field merely need to reach a few percent of equipartition for this to occur. Overall, these results have important implications for models of jet formation that require strong, large-scale magnetic fields to exist over a region of the inner accretion disk.

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Turbulence in molecular clouds - A new diagnostic tool to probe their origin

Cited by 5 publications

References 0 publications

Carbon-Rich Planet Formation in a Solar Composition Disk

Carbon-Rich Planet Formation in a Solar Composition Disk

Extracting Energy from Black Holes: The Relative Importance of the Blandford‐Znajek Mechanism

Advection of Magnetic Fields in Accretion Disks: Not So Difficult After All

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