NASA/ESA/Hubble
Artist’s impression of the red hypergiant VY Canis Major.
A team of astronomers led by the University of Arizona has created a detailed 3D image of the dying giant star.
A team led by researchers Ambesh Singh and Lucy Ziuris of the University of Arizona traced the distribution, directions and velocities of various molecules around a red hypergiant star known as VY Canis Major.
Their findings, which they presented on June 13 at the 240th meeting of the American Astronomical Society in Pasadena, California, offer unprecedented insight into the death of giant stars.
The work was carried out with collaborators Robert Humphreys of the University of Minnesota and Anita Richards of the University of Manchester, UK.
As extreme supergiantsalso known as hypergiants, are very rare and few exist in the Milky Way.
Examples include Betelgeuse, the second brightest star in the constellation of Orion, and NML Cygnus, also known as V1489 Cygnus, in the direction of the constellation Cygnus.
Unlike lower-mass stars, which are more likely to swell as they transition to the red giant phase but generally retain a spherical shape, hypergiants tend to undergo substantial mass losses as they form. structures complex and very irregular consists of arcs, clusters and nodes.
Located about 3009 light-years from Earth, VY Canis Major – or VY CMa for short – is a pulsating variable star in the constellation Canis Major.
Covering a range of 10,000 to 15,000 astronomical units (1 astronomical unit or AU is the average distance between the Earth and the Sun, about 150 million kilometers), VY CMa is possibly the most massive star in the Milky Wayaccording to Zyurys.
“Think of it like Betelgeuse on steroids,” said Ziuris, regent professor in the Department of Chemistry and Biochemistry at the University of Arizona and the Steward Observatory. “It’s much bigger, much more massive, and erupts every 200 years or so.”
The team chose to study VY CMa because it is considered one of the best examples of this type of star.
“We are particularly interested in what hypergiants do at the end of their lives,” said Singh, a fourth-year doctoral student and member of the Ziuris lab. “People used to think these massive stars were just went supernovabut we are no longer sure.
“If that were the case, we would see many more supernova explosions across the sky,” Zyurys added. “Now we think they might collapse into black holes silently, but we don’t know which ones end up this way, or why or how.”
Previous images of VY CMa by NASA’s Hubble Space Telescope and spectroscopy have shown distinct arcs and other clusters and nodes, many of which extend thousands of astronomical units from the central star.
To uncover more details about the processes by which hypergiant stars end their lives, the team began tracking specific molecules around the hypergiant and matching them to existing images of dust taken by the Hubble Space Telescope.
“No one has been able to get a complete picture of this star,” Zyuris said, explaining that his team set out to understand the mechanisms by which the star’s mass is released, which appear to be different from those of the smaller stars that make up the star. , your red giant stage at the end their lives.
“You don’t see this beautiful symmetrical mass loss, but convection cells that “shoot through” the star’s photosphere like giant bullets and eject mass in different directions,” Zyuris said. “They are similar to the coronal arcs seen on the Sun, but a billion times larger.”
The team used the Atacama Large Millimeter Array (ALMA) in Chile to track various molecules in material ejected from the star’s surface.
While some observations are still ongoing, preliminary maps have been made for sulfur oxide, sulfur dioxide, silica, phosphorus oxide, and sodium chloride. Based on these data, the team built an image of the structure of the global molecular stream VY CMa on a scale covering all the material ejected by the star.
“How molecules trace the arcs on the bodywhich tells us that the molecules and dust are well mixed,” said Singh.
“What’s great about molecular radio waves is that they give us speed information, unlike dust emissions, which are static,” he added.
By moving ALMA’s 48 antennas into various configurations, the researchers were able to obtain information about the directions and velocities of the molecules and map them to different regions of the hypergiant envelope in great detail, even correlating them with different mass ejection events over time. .
According to Singh, processing the data required some “hard work” in terms of processing power.
“At the moment we have processed almost a terabyte ALMA and we are still getting data that we have to analyze to get the best resolution possible,” he said.
“Only calibration and data cleansing requires up to 20,000 iterations, which takes a day or two for each molecule,” he adds.
“Thanks to these observations, we can now map them in the sky,” Zyurys added. “So far, only small parts of this huge structure have been studied, but you cannot understand the loss of mass and how these large stars die unless you look at the entire region. That’s why we wanted to create the complete picture.”
With financial support from the NSF (National Science Foundation), the team plans to publish their findings in cycle of scientific articles.
