Baby Pictures of a Massive Star

Astronomers hav​e imaged the same massive young star at an 18-year interval and comparing them to see how the star is forming.

Led by Carlos Carrasco-Gonzalez of the National Autonomous University of Mexico, the team used the Karl G. Jansky Very Large Array observatory in New Mexico to get radio telescope images of a massive protostar known as W75N(B)-VLA2 in 1996 and then again in 2014. A massive star is one that's many times the mass of our Sun; this one is estimated to be around eight times more massive. Their research is published in Science​.

"Now we understand more or less how a star like our Sun formed," said Carrasco-Gonzalez. "But for these massive stars, there are some theoretical problems that we don't have solved yet, and they are also very difficult to observe and detect."

Researchers therefore are interested to study massive stars and see how their formation may differ.

In this case, what they were particularly looking at is the winds around the star. In the first image, from 1996, you can see a visualization of the ionized winds ejected from the star; they're in quite a circular shape all around the star.

That's different from what you'd usually expect to see in star formation. Usually, stars throw material out into space in a "collimated" way, with the material coming only from the poles; here, the material is coming from all directions.

In the second image, however, the winds are spread out in an elongated elliptical shape, cast further out at the stars' poles. "All these observations suggest that we are observing in 'real time' the transition from an uncollimated outflow to a collimated outflow during the early life of a massive star," the paper states.

"Our theory is that this star, for any reason, has like a spherical wind, it's expelling material in all directions," explained Carrasco-Gonzalez. "But for some reason the material that arises from the poles moves faster than the material that is at the equatorial plane."

They think this is because wind around the star's equator is stopped by a "torus" of material around the star—the dusty ring you can see in the images. "In the poles, where there is no material at all, where the wind does not encounter any material, it moves faster," Carrasco-Gonzalez explained. Hence the elongated shape of the wind.

Perhaps, then, there are differences in how stars of this mass form compared to smaller stars.

Next, Carrasco-Gonzalez wants to look at the star's magnetic field, which is also theorized to play a role in star formation.