Evolution of rotating molecular cloud core with oblique magnetic field

Masahiro Machida, Tomoaki Matsumoto, Tomoyuki Hanawa, Kohji Tomisaka

Research output: Contribution to journalArticle

55 Citations (Scopus)

Abstract

We studied the collapse of rotating molecular cloud cores with inclined magnetic fields, based on three-dimensional numerical simulations. The numerical simulations start from a rotating Bonnor-Ebert isothermal cloud in a uniform magnetic field. The magnetic field is initially taken to be inclined from the rotation axis. As the cloud collapses, the magnetic field and rotation axis change their directions. When the rotation is slow and the magnetic field is relatively strong, the direction of the rotation axis changes to align with the magnetic field, as shown earlier by Matsumoto & Tomisaka. When the magnetic field is weak and the rotation is relatively fast, the magnetic field inclines to become perpendicular to the rotation axis. In other words, the evolution of the magnetic field and rotation axis depends on the relative strength of the rotation and magnetic field. Magnetic braking acts to align the rotation axis and magnetic field, while the rotation causes the magnetic field to incline through dynamo action. The latter effect dominates the former when the ratio of the angular velocity to the magnetic field is larger than a critical value Ω0/B0 > 0.39G1/2cs -1, where B0, Ω0, G, and cs denote the initial magnetic field, initial angular velocity, gravitational constant, and sound speed, respectively. When the rotation is relatively strong, the collapsing cloud forms a disk perpendicular to the rotation axis and the magnetic field becomes nearly parallel to the disk surface in the high-density region. A spiral structure appears due to the rotation and the wound up magnetic field in the disk.

Original languageEnglish
Pages (from-to)1227-1245
Number of pages19
JournalAstrophysical Journal
Volume645
Issue number2 I
DOIs
Publication statusPublished - Jul 10 2006

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molecular clouds
magnetic field
magnetic fields
angular velocity
gravitational constant
braking
simulation

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Evolution of rotating molecular cloud core with oblique magnetic field. / Machida, Masahiro; Matsumoto, Tomoaki; Hanawa, Tomoyuki; Tomisaka, Kohji.

In: Astrophysical Journal, Vol. 645, No. 2 I, 10.07.2006, p. 1227-1245.

Research output: Contribution to journalArticle

Machida, Masahiro ; Matsumoto, Tomoaki ; Hanawa, Tomoyuki ; Tomisaka, Kohji. / Evolution of rotating molecular cloud core with oblique magnetic field. In: Astrophysical Journal. 2006 ; Vol. 645, No. 2 I. pp. 1227-1245.
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