Using the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) in New Mexico, astronomers studied a youthful star catalogued as W75N(B)-VLA 2 located 4200 light-years from Earth. They were able to gauge the star’s progress by comparing images taken in 2014 with earlier VLA records of the same star dating from 1996.
Leader of the research team, Carlos Carrasco-Gonzalez of the Center of Radioastronomy and Astrophysics of the National Autonomous University of Mexico, termed the comparison “remarkable.”
When viewed in 1996, W75N(B)-VLA 2 can be seen at the center of a hot, ionized wind, ejected and expanding from the star in a near spherical formation. Some 28 years later, however, the hot wind has been reshaped as it encountered a dusty, donut shaped torus around the young star causing a pronounced elongation.
These dramatic changes, observed in real-time, present astronomers with a unique opportunity to study W75N(B)-VLA 2 over the next few years observing a very young star in the early stages of its formation.
Astronomers believe the star is forming in a dense, gaseous environment, but surrounded by a donut-shaped, dusty torus. W75N(B)-VLA 2 appears to go through phases lasting for several years when it ejects a hot, ionized wind.
As the ionized wind first “blows” it expands in all directions, broadly equidistantly. That explains the spherical shape around the star in the earlier image. As the stellar wind encounters the dusty torus, it’s slowed down. But the wind expanding outward along the poles of the torus moves more quickly since there is less resistance. This results in the elongated shape of the out-flowing wind in the 2014 image.
“In the span of only 18 years, we’ve seen exactly what we predicted,” Carrasco-Gonzalez commented.
Theoretical models exist explaining why the nearly-spherical expansion of such outflows is observed in the case of young stars much more massive than the Sun, while narrower, beam-like outflows were expected based on observations of less-massive, Sun-like stars at similar stages of development.
Scientists put W75N(B)-VLA 2’s size at roughly eight times more massive than our Sun. The more-uniform outflows of gas are seen in massive young stars during the first few thousand years of their existence, the stage at which W75N(B)-VLA 2 is believed to be.
“Our understanding of how massive young stars develop is much less complete than our understanding of how Sun-like stars develop,” Carrasco-Gonzalez explained, adding, “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.”
Carrasco-Gonzalez is part of an international team of astronomers drawn from Mexico, the Netherlands, Sweden, Spain, Korea, and Japan. Their findings are reported in the journal Science.
