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Tokyo Tech News

Constraining the strength of magnetic fields in planet-forming environments

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Published: February 12, 2015

Planets form in gaseous disks around young stars called protoplanetary disks. These disks are believed to evolve by interacting with magnetic fields in the interstellar space.

However, there is great uncertainty in the magnitude of the realistic range of the magnetic field strength within the disks because of the difficulty in direct astronomical measurements.

Now, Satoshi Okuzumi and Taku Takeuchi at Tokyo Institute of Technology, together with Takayuki Muto at Kogakuin University, have shown theoretically that there is an upper limit of the magnetic field strength in protoplanetary disks.

The team analyzed the transport of large-scale magnetic fields in a disk based on a mean-field transport theory known in astrophysics. By using a computer algebra system, they successfully derived the exact solution of the mean-field equation, which led to the discovery of the universal upper limit.

The derived upper limit explains well the range of the observed rates of gas accretion from disks onto the central star. The upper limit is also consistent with the observational fact that young stars have much smaller magnetic fluxes than parent molecular cloud cores.

This study is an important step towards understanding how the planet-forming environments evolve around young stars.

Upper limit on the large-scale vertical field strength (solid line) as a function of the distance from the central star, compared with the field strength required for disk accretion (dashed, dot-dashed, and dotted lines) together with the typical field strength of young stars (star symbol).

Upper limit on the large-scale vertical field strength (solid line) as a function of the distance from the central star, compared with the field strength required for disk accretion (dashed, dot-dashed, and dotted lines) together with the typical field strength of young stars (star symbol).

Reference

Authors:
Satoshi Okuzumi1, Taku Takeuchi1, and Takayuki Muto2
Title of original paper:
Radial Transport of Large-scale Magnetic Fields in Accretion Disks. I. Steady Solutions and an Upper Limit on the Vertical Field Strength
Journal, volume, pages and year:
The Astrophysical Journal 785, 127 (2014).
Digital Object Identifier (DOI):
Affiliations:
1Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2Division of Liberal Arts, Kogakuin University

Further information
Assistant Professor Satoshi Okuzumi
Department of Earth and Planetary Sciences
Graduate School of Science and Engineering
E-mail okuzumi@geo.titech.ac.jp
TEL +81-35-734-2616

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