Astronomers Amazed By Growth Of Massive Star W75N(B)-VLA 2


Astronomers say they've caught star formation in the act, seeing it as it is happening in a massive protostar more than 4,200 light years from Earth.

The star, W75N(B)-VLA 2, has been in the throes of a dramatic evolution over the course of just 18 years, as shown by a pair of images taken at the beginning and at the end of that cosmically brief interval.

In 1996, radio telescopes first detected a cloud in the star-forming region labeled W75N(B), a cloud with very little structure, a magnetic field that wasn't oriented in any particular direction, and a solar wind streaming away in all directions.

Writing in the journal Science, astronomers report observations last year showed the stellar winds had begun to align with the object's poles and its magnetic field was now aligned with the field of the larger surrounding cloud of dust and gas.

"The comparison [of the two images] is remarkable," says Carlos Carrasco-Gonzalez of the Center of Radioastronomy and Astrophysics at the National Autonomous University of Mexico.

"We're seeing this dramatic change in real time, so this object is providing us an exciting opportunity to watch over the next few years as a very young star goes through the early stages of its formation," says Carrasco-Gonzalez, the leader of the research project.

The astronomers have been studying the developing star with the National Science Foundation's Very Large Array radio telescope located around 50 miles west of Socorro, N.M.

The protostar is growing in a dense environment of dust and gas, within a surrounding ring, or torus, of dust. Hot ionized winds, ejected repeatedly by the growing star, at first can expand equally in every direction, creating a spherical shell around the nascent star.

Scientists say they think that when the winds hit the dust torus, they slow down, but at the torus's poles where there is less resistance they move more quickly, and the star's surrounding shell takes on a stretched, elongated shape -- as seen in the recent observations of W75N(B)-VLA 2.

"In the span of only 18 years, we've seen exactly what we predicted," Carrasco-Gonzalez says.

Carrasco-Gonzalez worked with international collaborators from Mexico, Sweden, the Netherlands, Spain, Japan and Korea. 

They estimate W75N(B)-VLA 2 to be about eight times more massive than our Sun.

"Our understanding of how massive young stars develop is much less complete than our understanding of how Sun-like stars develop," Carrasco-Gonzalez says. "It's going to be really great to be able to watch one as it changes. We expect to learn a lot from this object."

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