Artist's conception of the development of W75N(B)-VLA-2.. At left, a hot wind from the young star expands nearly spherically, as seen in 1996. At right, as seen in 2014, the hot wind has been shaped by encountering a dusty, donut-shaped torus around the star and appears elongated. Credit: Bill Saxton, NRAO/AUI/NSF. JPG image
VLA images of W75N(B)-VLA-2: Top, 1996; Bottom, 2014
Credit: Carrasco-Gonzalez, et al., NRAO/AUI/NSF. JPG image
A pair of images of a young star, made 18 years apart, has revealed a dramatic difference that is providing astronomers with a unique, "real-time" look at how massive stars develop in the earliest stages of their formation.
The astronomers used the National Science
Foundation's Karl G. Jansky Very Large Array (VLA) to study a massive
young star called W75N(B)-VLA 2, some 4200 light-years from Earth. They
compared an image made in 2014 with an earlier VLA image from 1996.
"The
comparison is remarkable," said Carlos Carrasco-Gonzalez of the Center
of Radioastronomy and Astrophysics of the National Autonomous University
of Mexico, leader of the research team. The 1996 image shows a compact
region of a hot, ionized wind ejected from the young star. The 2014
image shows that ejected wind deformed into an distinctly elongated
outflow.
"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," Carrasco-Gonzalez said.
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. 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.
"In the span of only 18 years, we've seen exactly what we predicted," Carrasco-Gonzalez said.
There
are theoretical models developed to explain why nearly-spherical
expansion of such outflows had been seen with young stars much more
massive than the Sun, when narrower, beam-like outflows were expected
based on observations of less-massive, Sun-like stars at similar stages
of development. W75N(B)-VLA 2 is estimated to be about 8 times more
massive than the Sun. The more-uniform outflows are seen in massive
young stars in the first few thousand years of their lives, the stage at
which W75N(B)-VLA 2 is thought 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 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," he added.
Carrasco-Gonzalez worked
with an international team of astronomers from Mexico, the Netherlands,
Sweden, Spain, Korea, and Japan. The scientists reported their
discovery in the journal Science.
The National Radio
Astronomy Observatory is a facility of the National Science Foundation,
operated under cooperative agreement by Associated Universities, Inc.
Contact:
Dave Finley, Public Information Officer
(575) 835-7302
dfinley@nrao.edu
