Press Archive

Alternative star formation theory debunked

Published 12/12/2005

Astrophysicist Richard Klein from the University of California, Berkeley and others used simulations run at the San Diego Supercomputer Center (SDSC) to explode one of two competing theories about how stars form inside immense clouds of interstellar gas. Using simulations that take into account the turbulence within a cloud collapsing to form a star, the researchers concluded that the "competitive accretion" model cannot explain what astronomers observe of star-forming regions studied to date.

The 10-year-old accretion model predicts that interstellar hydrogen clouds develop clumps in which several small cores - the seeds of future stars - form. These cores, less than a light year across, collapse under their own gravity and compete for gas in the surrounding clump, often gaining 10 to 100 times their original mass from the clump.

The alternative model, often termed the "gravitational collapse and fragmentation" theory, also presumes that clouds develop clumps in which proto-stellar cores form. But in this theory, the cores are large and though they may fragment into smaller pieces to form binary or multiple star systems, contain nearly all the mass they ever will.

Employing 256 parallel processors at SDSC, Klein's team ran their model for nearly two weeks to show that it accurately represented star formation dynamics. The model is a simulation of the complicated dynamics of gas inside a swirling, turbulent cloud of molecular hydrogen as it accretes onto a star. It is the first study of the effects of turbulence on the rate at which a star accretes matter as it moves through a gas cloud.

The models showed that turbulence in the core and surrounding clump would prevent accretion from adding much mass to a protostar.

"We have shown that, because of turbulence, a star cannot efficiently accrete much more mass from the surrounding clump," Klein said. "In our theory, once a core collapses and fragments, that star basically has all the mass it is ever going to have. If it was born in a low-mass core, it will end up being a low-mass star. If it's born in a high mass core, it may become a high-mass star."

The full technical paper is available in the November 17, 2005 issue of Nature. To access the story, log on to: http://www.nature.com/nature/journal/v438/n7066/full/nature04280.html