Constraints on the Formation and Evolution of Circumstellar Disks in Rotating Magnetized Cloud Cores

Basu, Shantanu

doi:10.1086/306494

Cited by 66 publications

(89 citation statements)

References 75 publications

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“…with 0 < ω < 0.5 a very important (as we will see) parameter which is determined by the background large scale magnetic field and cloud rotation (Basu 1998 gives a value of order 0.026); c s ≡ (k B T /µ) 1/2 is the isothermal speed of sound; µ = 2.33 m H is the mean particle weight of a fluid consisting of molecular hydrogen with a 10% [by number] helium admixture. This first stage of the cloud's evolution lasts for about 10 6 −10 7 years (Ciolek & Basu 2000;Ciolek & Basu 2001).…”

Section: Send Offprint Requests To: I Contopoulosmentioning

confidence: 59%

“…As a first step, we will assume that the mass inside r shock is initially distributed as m = m d r/r shock (Eq. (3), Saigo & Hanawa 1998), although a subsequent redistribution due to viscous torques is expected (Basu 1998). The exact mechanism of mass and angular momentum redistribution remain uncertain, thus we prefer at this point to consider the Keplerian disk at its very initial stage before any accretion process has taken place.…”

Section: The Magnetic Fieldmentioning

confidence: 99%

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The origin of molecular protostellar outflows

Contopoulos

Sauty

2001

A&A

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Abstract.We study the geometry of the large scale magnetic field threading the centrifugally supported circumstellar disk that forms in the inner few hundred AU of a dynamically collapsing protostellar molecular cloud core. The disk is highly turbulent, therefore highly diffusive, thus unable by itself to sufficiently stretch and bend the large scale magnetic field so as to launch magnetically driven winds from its surface. However, when we take proper account of the fact that the magnetic field is already highly stretched and bent in the outside dynamically collapsing cloud core, we discover that this contributes to significant outward magnetic field bending around the outer edge of the inner protoplanetary disk too. We obtain the field geometry self-consistently under general simplifying approximations. We also show how this magnetic field geometry leads naturally to strong magneto-centrifugally driven outflows from the surface of the disk, with mass loss rates a significant fraction of the accretion rate onto the inner disk. Our simple picture describes naturally the origin of the molecular winds observed during the end stages of protostellar cloud collapse.

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Section: Send Offprint Requests To: I Contopoulosmentioning

confidence: 59%

Section: The Magnetic Fieldmentioning

confidence: 99%

The origin of molecular protostellar outflows

Contopoulos

Sauty

2001

A&A

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“…Larson, 1969;Penston, 1969;Shu, 1977;Terebey et al, 1984;Shu et al, 1987;Stahler and Palla, 2004;McKee and Ostriker, 2007) and the importance of the magnetic field and the angular momentum of the initial cloud in determining the final properties of the protostar and its protostellar disc (e.g. Mestel and Spitzer, 1956;Strittmatter, 1966;Basu, 1998;Dapp and Basu, 2010) are of vital importance to our understanding of the universe.…”

Section: Star Formationmentioning

confidence: 99%

Star Formation and the Hall Effect

Wardle

2004

Astrophysics and Space Science

104

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Magnetic fields play an important role in star formation by regulating the removal of angular momentum from collapsing molecular cloud cores. Hall diffusion is known to be important to the magnetic field behaviour at many of the intermediate densities and field strengths encountered during the gravitational collapse of molecular cloud cores into protostars, and yet its role in the star formation process is not well-studied. This thesis describes a semianalytic self-similar model of the collapse of rotating isothermal molecular cloud cores with both Hall and ambipolar diffusion, presenting similarity solutions that demonstrate that the Hall effect has a profound influence on the dynamics of collapse.Two asymptotic power law similarity solutions to the collapse equations on the inner boundary are derived. The first of these represents a Keplerian disc in which accretion is regulated by the magnetic diffusion; with an appropriate value of the Hall diffusion parameter a stable rotationally-supported disc forms, but when the Hall parameter has the opposite sign disc formation is suppressed by the strong diffusion. The second solution describes the infall when the magnetic braking is so efficient at removing angular momentum from the core that no disc forms and the matter free falls onto the protostar.The full similarity solutions show that the size and sign of the Hall parameter can change the size of the protostellar disc by up to an order of magnitude and the accretion rate onto the protostar by 1.5 × 10 −6 M yr −1 when the ratio of the Hall to ambipolar diffusion parameters moves between the extremes of −0.5 ≤η H /η A ≤ 0.2. These variations (and their dependence upon the orientation of the magnetic field with respect to the axis of rotation) create a preferred handedness to the solutions that could be observed in protostellar cores using next-generation instruments such as ALMA.Hall diffusion also determines the strength of the magnetic diffusion and centrifugal shocks that bound the pseudo and rotationally-supported discs, and can introduce subshocks that further slow accretion onto the protostar. In cores that are not initially rotating Hall diffusion can even induce rotation, which could give rise to disc formation and resolve the magnetic braking catastrophe. The Hall effect clearly influences the dynamics of gravitational collapse and its role in controlling the magnetic braking and radial diffusion of the field would be worth exploring in future numerical simulations of star formation. Statement of CandidateI certify that the work in this thesis, entitled "Star Formation and the Hall Effect", has not previously been submitted for a degree nor has it been submitted as part of requirements for a degree to any other university or institution other than Macquarie University.I also certify that this thesis is an original piece of research and that it has been written by myself. Any help and assistance that I have received in my research work and the preparation of the thesis itself have been appropriatel...

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“…, (e.g., Larson 1969;Shu 1977;Basu 1998). For temperatures around 10 K, the infall accretion rate is of the order of 1 until it reaches a steady state.…”

Section: Fully Turbulent Disk Modelmentioning

confidence: 99%

On the Formation of Super-Earths With Implications for the Solar System

Martin

Livio

2016

ApJ

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We first consider how the level of turbulence in a protoplanetary disk affects the formation locations for the observed close-in super-Earths in exosolar systems. We find that a protoplanetary disk that includes a dead zone (a region of low turbulence) has substantially more material in the inner parts of the disk, possibly allowing for in situ formation. For the dead zone to last the entire lifetime of the disk requires the active layer surface density to be sufficiently small,  S -100 g cm crit 2 . Migration through a dead zone may be very slow and thus super-Earth formation followed by migration toward the star through the dead zone is less likely. For fully turbulent disks, there is not enough material for in situ formation. However, in this case, super-Earths can form farther out in the disk and migrate inward on a reasonable timescale. We suggest that both of these formation mechanisms operate in different planetary systems. This can help to explain the observed large range in densities of super-Earths because the formation location determines the composition. Furthermore, we speculate that super-Earths could have formed in the inner parts of our solar system and cleared the material in the region inside of Mercury's orbit. The super-Earths could migrate through the gas disk and fall into the Sun if the disk was sufficiently cool during the final gas disk accretion process. While it is definitely possible to meet all of these requirements, we don't expect them to occur in all systems, which may explain why the solar system is somewhat special in its lack of super-Earths.

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Constraints on the Formation and Evolution of Circumstellar Disks in Rotating Magnetized Cloud Cores

Cited by 66 publications

References 75 publications

The origin of molecular protostellar outflows

The origin of molecular protostellar outflows

Star Formation and the Hall Effect

On the Formation of Super-Earths With Implications for the Solar System

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