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Theory of Cluster Formation: Effects of Magnetic Fields

Published online by Cambridge University Press:  27 April 2011

Fumitaka Nakamura  and
Zhi-Yun Li
Fumitaka Nakamura
Affiliation:
Division of Theoretical Astrophysics, National Astronomical Observatory of Japan Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan email: fumitaka.nakamura@nao.ac.jp
Zhi-Yun Li
Affiliation:
Astronomy Department, University of Virginia, P. O. Box 400325, Charlottesville, VA 22904 email: zl4h@virginia.edu
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Abstract

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Stars form predominantly in clusters inside dense clumps of molecular clouds that are both turbulent and magnetized. The typical size and mass of the cluster-forming clumps are ~1 pc and ~102 – 103 M⊙, respectively. Here, we discuss some recent progress on numerical simulations of clustered star formation in such parsec-scale dense clumps with emphasis on the role of magnetic fields. The simulations have shown that magnetic fields tend to slow down global gravitational collapse and thus star formation, especially in the presence of protostellar outflow feedback. Even a relatively weak magnetic field can retard star formation significantly, because the field is amplified by supersonic turbulence to an equipartition strength. However, in such a case, the distorted field component dominates the uniform one. In contrast, if the field is moderately-strong, the uniform component remains dominant. Such a difference in the magnetic structure is observed in simulated polarization maps of dust thermal emission. Recent polarization measurements show that the field lines in nearby cluster-forming clumps are spatially well-ordered, indicative of a rather strong field. In such strongly-magnetized clumps, star formation should proceed relatively slowly; it continues for at least several global free-fall times of the parent dense clump (tff ~ a few × 105 yr).

Keywords

ISM: cloudsISM: jets and outflowsISM: magnetic fieldsMHDpolarizationstars: formationturbulence
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 6 , Symposium S270: Computational Star Formation , May 2010 , pp. 115 - 122
Copyright
Copyright © International Astronomical Union 2011

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