1. Astrophysics Department, Princeton University, Princeton, New Jersey 08544, USA
2. Physics Department,
3. Astronomy Department, UC Berkeley, Berkeley, California 94720, USA
4. Lawrence Livermore National Laboratory, Livermore, California 94550, USA

Correspondence to: Mark R. Krumholz¹ Correspondence and requests for materials should be addressed to M.R.K. (Email: krumholz@astro.princeton.edu).

Abstract

There are two dominant models of how stars form. Under gravitational collapse, star-forming molecular clumps, of typically hundreds to thousands of solar masses (M), fragment into gaseous cores that subsequently collapse to make individual stars or small multiple systems^{1, 2, 3}. In contrast, competitive accretion theory suggests that at birth all stars are much smaller than the typical stellar mass (0.5M), and that final stellar masses are determined by the subsequent accretion of unbound gas from the clump^{4, 5, 6, 7, 8}. Competitive accretion models interpret brown dwarfs and free-floating planets as protostars ejected from star-forming clumps before they have accreted much mass; key predictions of this model are that such objects should lack disks, have high velocity dispersions, form more frequently in denser clumps^{9, 10, 11}, and that the mean stellar mass should vary within the Galaxy⁸. Here we derive the rate of competitive accretion as a function of the star-forming environment, based partly on simulation¹², and determine in what types of environments competitive accretion can occur. We show that no observed star-forming region can undergo significant competitive accretion, and that the simulations that show competitive accretion do so because the assumed properties differ from those determined by observation. Our result shows that stars form by gravitational collapse, and explains why observations have failed to confirm predictions of the competitive accretion model.

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.