Scientists track growth of "an embryo of a star"

Scientists are getting a rare chance to watch a star form.

In a paper published Thursday in Science, Carlos Carrasco-Gonzalez and his colleagues said they were able to compare images taken 18 years apart of a massive star called W75N(B)-VLA 2, which is about eight times more massive than the sun.

Using the Karl G. Jansky Very Large Array, a collection of 27 telescopes at an observatory in New Mexico, the researchers compared images from 2014 and 1996 of the protostar some 4,200 light years away from Earth and noticed visible milestones of its development.

"This is the first time we have seen the behavior of a massive star so young. It is like an embryo of a star," Carrasco-Gonzalez, of the Center of Radioastronomy and Astrophysics of the National Autonomous University of Mexico and leader of the research team, said of the formation that will take hundreds of thousands of years.

"We want to know how these stars are formed," he said. "This is important because complex elements are needed in the universe and we think those elements are within massive stars. At the end of their life, they release a lot of material that could be used to form planets and solar systems."

Carasco-Gonzalez and his colleagues found this object behaved much differently as it aged. The 1996 image shows a compact region of a hot, ionized wind ejected from the young star. In contrast, the 2014 image shows that ejected wind deformed into a distinctly elongated outflow.

"The comparison is remarkable," Carrasco-Gonzalez said. "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."

The scientists believe the young star is forming in a dense, gaseous environment, and is surrounded by a doughnut-shaped, dusty torus. The star has episodes in which it ejects a hot, ionized wind for several years.

Initially, the wind expands in all directions, forming a spherical shell around the star. As it ages, the wind slows as it hits the dusty torus. Then, wind can be seen expanding outward along the poles of the torus, resulting in the elongated shape of the outflow.

Carrasco-Gonzalez said the star's behavior matched the theoretical models, which predicted a spherical expansion of gas outflows in the first few thousand years of a massive star's life.

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

Qizhou Zhang, a radio astronomer from Harvard-Smithsonian Center for Astrophysics who specializes in star formation, called the findings "interesting and surprising," adding that it would go a ways toward understanding the formation of these more massive stars.

"The process of forming sun-like stars is more or less understood. For those stars 10 times more massive than the sun, we are sort of beginning to understand their formation process," Zhang said.

Next up for the researchers is studying the young star's magnetic field, which Carrasco-Gonzalez said is another important component in its formation.