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: ms.pdf

FIGURES: figure1.pdf figure2.pdf

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: full paper