A multinational team of astronomers, led Dr Carlos Carrasco-Gonzalez of the National Autonomous University of Mexico, used the Karl G. Jansky Very Large Array (VLA) to make two separate observations of a protostar called W75N(B)-VLA 2 almost two decades apart. They were surprised to discover that the object has evolved from a compact source into an elongated one over such a relatively short period of time.
Artist’s impression of the development of the massive protostar W75N(B)-VLA-2. Top: a hot wind from the star expands nearly spherically, as seen in 1996. Bottom: as seen in 2014, the hot wind has been shaped by encountering a dusty, donut-shaped torus around the star and appears elongated. Image credit: Bill Saxton / NRAO / AUI / NSF.
The object in question, W75N(B)-VLA 2, is a massive young star located approximately 4,200 light-years away.
A 1996 image of the star shows a compact region of a hot, ionized wind ejected from the young star, while a 2014 image shows that ejected wind deformed into a distinctly elongated outflow.
“We are 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,” explained Dr Carrasco-Gonzalez, who is the first author of the paper published in the journal Science.
Dr Carrasco-Gonzalez and his colleagues believe W75N(B)-VLA 2 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.
At first, that wind can expand in all directions, and so forms a spherical shell around the star. Later, the wind hits the dusty torus, which slows it.
Wind expanding outward along the poles of the torus, where there is less resistance, moves more quickly, resulting in an elongated shape for the outflow.
“Our understanding of how massive young stars develop is much less complete than our understanding of how Sun-like stars develop,” Dr Carrasco-Gonzalez said.
“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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C. Carrasco-González et al. Observing the onset of outflow collimation in a massive protostar. Science, vol. 348, no. 6230, pp. 114-117; doi: 10.1126/science.aaa7216
