3,265 research outputs found
Present-Day Star Formation: Protostellar Outflows and Clustered Star Formation
Stars form predominantly in clusters inside dense clumps of turbulent,
magnetized molecular clouds. The typical size and mass of the cluster-forming
clumps are \sim 1 pc and \sim 10^2 - 10^3 M_\odot, respectively. Here, we
discuss some recent progress on theoretical and observational studies of
clustered star formation in such parsec-scale clumps with emphasis on the role
of protostellar outflow feedback. Recent simulations indicate that protostellar
outflow feedback can maintain supersonic turbulence in a cluster-forming clump,
and the clump can keep a virial equilibrium long after the initial turbulence
has decayed away. In the clumps, star formation proceeds relatively slowly; it
continues for at least several global free-fall times of the parent dense clump
(t_{ff}\sim a few x 10^5 yr). The most massive star in the clump is formed at
the bottom of the clump gravitational potential well at later times through the
filamentary mass accretion streams that are broken up by the outflows from
low-mass cluster members. Observations of molecular outflows in nearby
cluster-forming clumps appear to support the outflow-regulated cluster
formation model.Comment: 8 pages, 5 figures proceedings of the First Stars IV 2012 Conference
held in Kyoto, Japa
Theory of Cluster Formation: Effects of Magnetic Fields
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 pc and 10 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 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 ( a few yr).Comment: 8 pages, proceedings of Computational Star Formation (IAU 270
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