Thermal Stability of a Thin Disk With Magnetically Driven Winds

Li, Shuang-Liang; Begelman, Mitchell C.

doi:10.1088/0004-637x/786/1/6

Cited by 50 publications

(64 citation statements)

References 37 publications

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“…Crudely assuming that the peak ionization rate in Saturn's sunlit ionosphere is similar as in Titan's ionosphere (∼30 cm −3 ∕s for similar SZA, see, e.g., Vigren et al, 2013) the relation then gives ≈ 1.3 × 10 −7 cm 3 ∕s near the peak. This may be viewed as a crude upper limit of ; if electrons are lost partly to charging of macromolecules/grains, the estimated can to first approximation be corrected by a multiplicative factor n e ∕n i (Vigren et al, 2014).…”

Section: Ionospheric Density Altitude Profile Modelmentioning

confidence: 99%

Saturn's Ionosphere: Electron Density Altitude Profiles and D‐Ring Interaction From The Cassini Grand Finale

Hadid

Wahlund

Persoon

et al. 2019

Geophysical Research Letters

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We present the electron density (ne) altitude profiles of Saturn's ionosphere at near‐equatorial latitudes from all 23 orbits of Cassini's Grand Finale. The data are collected by the Langmuir probe part of the Radio and Plasma Wave Science investigation. A high degree of variability in the electron density profiles is observed. However, organizing them by consecutive altitude ranges revealed clear differences between the southern and northern hemispheres. The ne profiles are shown to be more variable and connected to the D‐ring below 5,000 km in the southern hemisphere compared to the northern hemisphere. This observed variability is explained to be a consequence of an electrodynamic interaction with the D‐ring. Moreover, a density altitude profile is constructed for the northern hemisphere indicating the presence of three different ionospheric layers. Similar properties were observed during Cassini's final plunge, where the main ionospheric peak is crossed at ∼1,550‐km altitude.

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Section: Ionospheric Density Altitude Profile Modelmentioning

confidence: 99%

Saturn's Ionosphere: Electron Density Altitude Profiles and D‐Ring Interaction From The Cassini Grand Finale

Hadid

Wahlund

Persoon

et al. 2019

Geophysical Research Letters

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“…The structure of the disk will be altered in the presence of magnetic outflows (Li & Cao 2009;Cao & Spruit 2013;Li 2014;Li & Begelman 2014). The angular momentum equation for a steady ADAF with outflows is…”

Section: Criṫmentioning

confidence: 99%

An Accretion Disk-Outflow Model for Hysteretic State Transition in X-Ray Binaries

Cao

2016

ApJ

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We suggest a model of the advection-dominated accretion flow (ADAF) with magnetically driven outflows to explain the hysteretic state transition observed in X-ray binaries (XRBs). The transition from a thin disk to an ADAF occurs when the mass accretion rate is below a critical value. The critical mass accretion rate for the ADAF can be estimated by equating the equilibration timescale to the accretion timescale of the ADAF, which is sensitive to its radial velocity. The radial velocity of thin disks is very small, which leads to the advection of the external field in thin disks becoming very inefficient. ADAFs are present in the low/hard states of XRBs, and their radial velocity is large compared with the thin disk. The external field can be dragged inward efficiently by the ADAF, so a strong large-scale magnetic field threading the ADAF can be formed, which may accelerate a fraction of gas in the ADAF into the outflows. Such outflows may carry away a large amount of angular momentum from the ADAF, which significantly increases the radial velocity of the ADAF. This leads to a high critical mass accretion rate, below which an ADAF with magnetic outflows can survive. Our calculations show that the critical luminosity of the ADAF with magnetic outflows can be one order of magnitude higher than that for a conventional ADAF, if the ratio of gas to magnetic pressure 4 b~in the disk. This can naturally explain the hysteretic state transition observed in XRBs.

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“…This kind of symmetry is widely adopted in the studies of accretion disks (e.g. Blandford & Payne 1982;Lovelace et al 1994;Cao 2011;Li & Begelman 2014) 3 . Thus we have,…”

Section: Basic Mhd Equationsmentioning

confidence: 99%

Two-dimensional inflow-wind solution of black hole accretion with an evenly symmetric magnetic field

Mosallanezhad

Yuan

2015

Mon. Not. R. Astron. Soc.

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We solve the two-dimensional magnetohydrodynamic (MHD) equations of black hole accretion with the presence of magnetic field. The field includes a turbulent component, whose role is represented by the viscosity, and a large-scale ordered component. The latter is further assumed to be evenly symmetric with the equatorial plane. The equations are solved in the r − θ plane of a spherical coordinate by assuming timesteady and radially self-similar. An inflow-wind solution is found. Around the equatorial plane, the gas is inflowing; while above and below the equatorial plane at a certain critical θ angle, θ ∼ 47 • , the inflow changes its direction of radial motion and becomes wind. The driving forces are analyzed and found to be the centrifugal force and the gradient of gas and magnetic pressure. The properties of wind are also calculated. The specific angular momentum of wind is found to be significantly larger than that of inflow, thus wind can transfer angular momentum outward. These analytical results are compared to those obtained by the trajectory analysis based on MHD numerical simulation data and good agreements are found.

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Thermal Stability of a Thin Disk With Magnetically Driven Winds

Cited by 50 publications

References 37 publications

Saturn's Ionosphere: Electron Density Altitude Profiles and D‐Ring Interaction From The Cassini Grand Finale

Saturn's Ionosphere: Electron Density Altitude Profiles and D‐Ring Interaction From The Cassini Grand Finale

An Accretion Disk-Outflow Model for Hysteretic State Transition in X-Ray Binaries

Two-dimensional inflow-wind solution of black hole accretion with an evenly symmetric magnetic field

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