Massive Star Formation in 100,000 years
from Turbulent and Pressurized Molecular Clouds
Christopher F. McKee and Jonathan C. Tan
Nature, 416, 59, March 7th, 2002,
Massive stars (with mass m_* > 8 solar masses) are
fundamental to the evolution of galaxies, because they produce heavy
elements, inject energy into the interstellar medium, and possibly
regulate the star formation rate. The individual star formation time,
t_*f, determines the accretion rate of the star; the value of the
former quantity is currently uncertain by many orders of
magnitude[Ref:1-6], leading to other
astrophysical questions. For example, the variation of t_*f with
stellar mass dictates whether massive stars can form simultaneously
with low-mass stars in clusters. Here we show that t_*f is
determined by conditions in the star's natal cloud, and is typically
~10^5 yr. The corresponding mass accretion rate depends on the
pressure within the cloud - which we relate to the gas surface
density - and on both the instantaneous and final stellar masses.
Characteristic accretion rates are sufficient to overcome radiation
pressure from ~100 solar mass protostars, while simultaneously driving
intense bipolar gas outflows. The weak dependence of t_*f on the
final mass of the star allows high- and low-mass star formation to
occur nearly simultaneously in clusters
TEXT:
FIGURES:
The Formation of Massive Stars and Star Clusters
Jonathan C. Tan and Christopher F. McKee
in Hot Star Workshop III: The Earliest Phases of Massive Star Birth, ASP Conference Series, Vol. 2??, 2002, Paul A. Crowther, ed.
We model the formation of high-mass stars, specifying the accretion
rate in terms of the instantaneous and final mass of the star, the
ambient pressure of the star-forming region and the form of polytropic
pressure support of the pre-stellar gas core. The high pressures
typical of Galactic regions of massive star formation allow a
100 solar mass star to form in ~10^5 years with a final
accretion rate ~10^-3 solar masses per year. By modeling
protostellar evolution we predict the properties of several nearby
massive protostars. We model cluster formation by applying this theory
to many stars. We use the observed intensity of outflows from
protoclusters to estimate the star formation rate, finding that
clusters take at least several free-fall times to form; for a cluster
similar to the Orion Nebula Cluster, we predict a formation timescale
~1x10^6 years.
TEXT:
jt@astro.princeton.edu