Watching the violent death of a rare, extreme supergiant star

The artistic impression of the red hypergiant star VI Canis Majoris. Located about 3,009 light-years from Earth, VI Canis Majoris is probably the most massive star on the Milky Way. Credit: NASA / ESA / Hubble / R. Humphreys, University of Minnesota / J. Olmsted, STScI / hubblesite.org

By tracking molecular emissions in the eruption around the red hypergiant star VI Canis Majoris, astronomers have obtained the first detailed map of the star’s mantle, which sheds light on the mechanisms involved in the final stages of the extreme supergiant star.

A team of astronomers led by the University of Arizona created a detailed, three-dimensional image of a dying hypergiant star. The team, led by Arizona researchers Ambesh Singh and Luci Ziuris, tracked the distribution, directions and velocities of various molecules surrounding a red hypergiant star known as VI Canis Majoris.

Their findings, which were presented on June 13, 2022 at the 240th meeting of the American Astronomical Society in Pasadena, California, offer insight, on an unprecedented scale, into the processes that accompany the death of giant stars. The work was done with collaborators Robert Humphries of the University of Minnesota and Anita Richards of the University of Manchester in the United Kingdom.

Extreme supergiant stars known as hypergiants are very rare, with only a few known to exist in[{” attribute=””>Milky Way. Examples include Betelgeuse, the second brightest star in the constellation Orion, and NML Cygni, also known as V1489 Cygni, in the constellation Cygnus. Unlike stars with lower masses – which are more likely to puff up once they enter the red giant phase but generally retain a spherical shape – hypergiants tend to experience substantial, sporadic mass loss events that form complex, highly irregular structures composed of arcs, clumps, and knots.

Located about 3,009 light-years from Earth, VY Canis Majoris – or VY CMa, for short – is a pulsating variable star in the slightly southern constellation of Canis Major. Spanning anywhere from 10,000 to 15,000 astronomical units (with 1 AU being the average distance between Earth and the sun) VY CMa is possibly the most massive star in the Milky Way, according to Ziurys.

“Think of it as Betelgeuse on steroids,” said Ziurys, a Regents Professor with joint appointments in UArizona Department of Chemistry and Biochemistry and Steward Observatory, both part of the College of Science. “It is much larger, much more massive and undergoes violent mass eruptions every 200 years or so.”

The team chose to study VY CMa because it is one of the best examples of these types of stars.

“We are particularly interested in what hypergiant stars do at end of their lives,” said Singh, a fourth-year doctoral student in Ziurys’ lab. “People used to think these massive stars simply evolve into supernovae explosions, but we are no longer sure about that.”

“If that were the case, we should see many more supernovae explosions across the sky,” Ziurys added. “We now think they might quietly collapse into black holes, but we don’t know which ones end their lives like that, or why that happens and how.”

Previous imaging of VY CMa with

“The molecules trace the arcs in the envelope, which tells us molecules and dust are well-mixed,” Singh said. “The nice thing about emissions of molecules at radio wavelengths is that they provide us with velocity information, as opposed to the dust emission, which is static.”

By moving ALMA’s 48 radio dishes into different configurations, the researchers were able to obtain information about the directions and velocities of the molecules and map them across the different regions of the hypergiant’s envelope in considerable detail, even correlating them to different mass ejection events over time.

Processing the data required some heavy lifting in terms of computing power, Singh said.

“So far, we have processed almost a terabyte from ALMA, and we still receive data that we have to go through to get the best resolution possible,” he said. “Just calibrating and cleaning the data requires up to 20,000 iterations, which takes a day or two for each molecule.”

“With these observations, we can now put these on maps on the sky,” Ziurys said. “Until now, only small portions of this enormous structure had been studied, but you can’t understand the mass loss and how these big stars die unless you look at the entire region. That’s why we wanted to create a complete image.”

With funding from the National Science Foundation, the team plans to publish its findings in a series of papers.

Meeting: 240th meeting of the American Astronomical Society


#Watching #violent #death #rare #extreme #supergiant #star