Free Astronomy Magazine March-April 2023

14 ASTRO PUBLISHING Hydrogen masers reveal new secrets of a massive star by ALMA Observatory W hile using the Atacama Large Millimeter/submil- limeter Array (ALMA) to study the masers around oddball star MWC 349A scientists discovered something unexpected: a previously unseen jet of material launching from the star’s gas disk at impossibly high speeds. What’s more, they be- lieve the jet is caused by strong mag- netic forces surrounding the star. The discovery could help researchers to understand the nature and evolu- tion of massive stars and how hydro- gen masers are formed in space. The new observations were pre- sented in a press conference at the 241 st meeting of the American As- tronomical Society (AAS) in Seattle, Washington. Located roughly 3,900 light-years away from Earth in the constellation Cygnus, MWC 349A’s unique fea- tures make it a hot spot for scientific research in optical, infrared, and radio wavelengths. The massive star —roughly 30 times the mass of the Sun— 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 am- plify microwave radio emissions, making it easier to study processes that are typically too small to see. It is this unique feature that allowed scientists to map MWC 349A’s disk in detail for the first time. “A maser is like a naturally occurring laser,” said Sirina Prasad, an under- graduate research assistant at the Center for Astrophysics | Harvard & Smithsonian (CfA), and the primary author of the paper. “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.” Leveraging the resolving power of ALMA’s Band 6, developed by the US National Science Foundation’s Na- tional Radio Astronomy Observatory (NRAO), the team was able to use the masers to uncover the previously unseen structures in the star’s imme- diate environment. Qizhou Zhang, a senior astrophysicist at CfA, and the project’s principal investigator added, “We used masers generated by hydrogen to probe the physical and dynamic structures in the gas surrounding MWC 349A and re- vealed a flattened gas disk with a di- ameter of 50 au, approximately the size of the Solar System, confirming the near-horizontal disk structure of the star. We also found a fast-mov- ing jet component hidden within the winds flowing away from the star.” The observed jet is ejecting material away from the star at a blis- tering 500 km per second. That’s akin to traveling the distance be- tween San Diego, California and Phoenix, Arizona in the literal blink of an eye. According to re- searchers, 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 m a g n e - tohydro- dynamic wind — a type of w i n d MARCH-APRIL 2023