The jet observed by the Atacama Large Millimeter/submillimeter Array (ALMA) is ejecting material away from MWC 349A at a blistering 500 km per second (311 miles per second) and is likely launched by a magnetohydrodynamic wind — a type of wind whose movement is dictated by the interplay between the star’s magnetic field and gases present in its surrounding disk.
This artist’s conception shows a zoomed in view of MWC 349A and its surrounding disk of gas and dust that are being shaped by the winds and high-speed jet. Image credit: ALMA / ESO / NAOJ / NRAO / M. Weiss, NRAO, AUI & NSF.
MWC 349A is a massive star some 3,900 light-years away from Earth in the constellation of Cygnus.
Also known as SDSS J203245.51+403936.6, the star has a mass of 30 solar masses.
MWC 349A is one of the brightest radio sources in the sky, and one of only a handful of objects known to have hydrogen masers.
These masers amplify microwave radio emissions, making it easier to study processes that are typically too small to see.
It is this unique feature that allowed Sirina Prasad from the Harvard & Smithsonian’s Center for Astrophysics and colleagues to map MWC 349A’s disk in detail for the first time.
“A maser is like a naturally occurring laser,” Prasad said.
“It’s an area in outer space that emits a really bright kind of light.”
“We can see this light and trace it back to where it came from, bringing us one step closer to figuring out what’s really going on.”
The study authors were able to use the masers to uncover the previously unseen structures in MWC 349A’s immediate environment.
“We used masers generated by hydrogen to probe the physical and dynamic structures in the gas surrounding MWC 349A and revealed a flattened gas disk with a diameter of 50 AU, approximately the size of the Solar System, confirming the near-horizontal disk structure of the star,” said Dr. Qizhou Zhang, also from the Harvard & Smithsonian’s Center for Astrophysics.
“We also found a fast-moving jet component hidden within the winds flowing away from the star.”
The observed jet is ejecting material away from the star at a blistering 500 km per second.
According to researchers, it is probable that a jet moving this fast is being launched by a magnetic force.
In the case of MWC 349A, that force could be a magnetohydrodynamic wind — a type of wind whose movement is dictated by the interplay between the star’s magnetic field and gases present in its surrounding disk.
“Our previous understanding of MWC 349A was that the star was surrounded by a rotating disk and photo-evaporating wind,” Prasad said.
“Strong evidence for an additional collimated jet had not yet been seen in this system.”
“Although we don’t yet know for certain where it comes from or how it is made, it could be that a magnetohydrodynamic wind is producing the jet, in which case the magnetic field is responsible for launching rotating material from the system.”
“This could help us to better understand the disk-wind dynamics of MWC 349A, and the interplay between circumstellar disks, winds, and jets in other star systems.”
The researchers will present their findings this week at the 241st meeting of the American Astronomical Society (AAS 241) in Seattle, Washington.
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S. Prasad et al. 2023. Using ALMA to Spatially Resolve Hydrogen Recombination Line Maser Emission from MWC 349A. AAS 241, program number: 474.04
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