Massive Star Formation Relies on Cosmic Doughnuts
Artist's Conception of Young Star Showing Motions Detected in G24 A1:(1) Infall toward torus, (2) Rotation and (3) outflow.
Credit: Bill Saxton, NRAO/AUI/NSF

Observations confirmed a leading theory that a doughnut-shaped ring of material could be responsible for the formation of massive stars, scientists reported today.

Smaller stars typically form when clouds of dust and gas collapse into a ball of compact material.

Stars that are 10 times more massive than the Sun, however, generate powerful stellar radiation, which can prevent the accumulation of material.

Doughnut disk

One model suggests that the radiation shoots out stronger at the poles of the star and is much weaker in the equator regions. Matter therefore forms a whirling disk, much like a doughnut, around the equator of the star. Most of the radiation escapes without hitting the disk so material keeps falling onto the star from the disk.

"If this model is correct, there should be material falling inward, rushing outward and rotating around the star all at the same time," said leader Maria Teresa Beltran, of the University of Barcelona in Spain.

Beltran and colleagues found one such star, G24 A1, a young object some 25,000 light-years from Earth and up to 20 times more massive than our Sun.

"For the first time, we have revealed the simultaneous presence in the same massive object of material moving outward, material moving inward, and rotation," Beltran said. "These three elements, outflow, infall and rotation, are commonly found during the formation process of low mass stars."

Tracing gas

Using the National Science Foundation's Very Large Array (VLA) radio telescope, the researchers traced the inward motion of the material.

"By studying the velocity field of the gas we detected a Doppler shift toward positive velocities of the surrounding gas, which indicates that the gas is moving inward the star," Beltran told SPACE.com.

The Doppler shift in the frequency of radio waves emitted by ammonia molecules present in the material gave scientist information on the motion of the gas.

Beltran says that the detection of gas falling inward toward the star is an important milestone and supports one of several proposed ways for massive stars to accumulate their great bulk. But she does not exclude the theory of smaller star collision.

"We think that the coalescence mechanism to form massive stars could still be required to form even more massive stars, or to form massive stars where the stellar densities are very large."

The study is detailed in the Sept. 28 issue of the journal Nature.