A new map of one of the most massive stars in our galaxy sheds light on what happens in the final stages of a giant star’s death.
Astronomers have created a detailed 3D map of VY Canis Majoris, a dying red hypergiant star located more than 3,000 light years from Earth. They found that the way this rare supergiant star loses mass is analogous to coronal arcs – loops of plasma that burst from the Sun – but on a scale billions of times greater.
By using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the team, led by University of Arizona researchers Ambesh Singh and Lucy Ziurys, traced the distributions and velocities of molecules as they swirled around VY Canis Majoris and mapped them. mapped onto structures of ejected material that span billions of miles.
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VY Canis Majoris is a pulsating variable star in the constellation Canis Major with an estimated mass 17 times that of the Sun and a radius of 10,000 to 15,000 astronomical units (AU). (One AU is the average distance between Earth and the sun: about 93 million miles, or 150 million kilometers.)
Only a few hypergiants are known to exist in the Milky Wayincluding Betelgeuse and NML Cygni, and VY Canis Majoris is one of the best examples of this type of rare star, according to the researchers.
“Think of it like Betelgeuse on steroids,” Ziurys said in a statement. “It’s much larger, much more massive, and experiences violent massive eruptions every 200 years or so.”
This means that the study of VY Canis Majoris offers a rare opportunity for astronomers to better understand the processes that occur when an extremely large star reaches the end of its life cycle. In particular, astronomers wanted to understand the mechanisms by which this star loses mass.
The agony of these massifs stars differ from those of lower mass stars, such as the sun, which swell and enter a red giant phase where they run out of hydrogen – the fuel that powers nuclear fusion – and can no longer defend themselves against gravitational collapse.
Instead, massive stars appear to undergo mass loss events as they enter this phase of their existence. These events are sporadic and substantial, with the lost material forming complex and highly irregular structures composed of arcs, tufts, and knots that can extend thousands of AU from the massive central star.
“We’re particularly interested in what hypergiant stars do at the end of their lives,” Singh said. “People thought these massive stars were just evolving into supernova explosions, but we’re not sure anymore.”
The team thinks that if these massive stars evolve into supernovae, astronomers would theoretically observe more of these stellar explosions. So they came up with another hypothesis.
“We now think they [hypergiant stars] could quietly collapse into black holes,” Ziurys said. “But we don’t know which ones end their lives like that, or why and how it happens.”
Big Dog VY Imaging
This isn’t the first time astronomers have imaged the arcs, tufts and nodes that radiate from VY Canis Majoris; the The Hubble Space Telescope and spectroscopy were used to image these massive structures. With this new work, the team traced some molecules around the hypergiant star, then mapped those findings onto Hubble images of dust around the central star. This revealed hidden details about the processes involved at the end of the lives of hypergiant stars, including details about how VY Canis Majoris loses mass.
“You don’t see this nice symmetrical mass loss, but rather convection cells blowing through the star’s photosphere like giant bullets and ejecting mass in different directions,” Ziurys said. “These are analogous to the coronal arcs seen in the sun, but a billion times larger.”
The observations of the VY Canis Majoris team with ALMA are still in their infancy. Yet despite this, even this preliminary map of sulfur oxide, sulfur dioxide, silicon oxide, phosphorus oxide, and sodium chloride helped the researchers build a picture of the flow structure. molecule of the massive star. And this image is large enough to encompass all the material ejected by the red hypergiant.
“The molecules trace the arcs in the envelope, which tells us that the molecules and the dust are well mixed,” Singh said. “The nice thing about molecular emissions at radio wavelengths is that they give us velocity information, as opposed to dust emission, which is static.”
By adjusting the configuration of ALMA’s 66 radio telescopes spread across Chile’s Atacama Desert, astronomers gathered details about the directions and speeds of molecules around VY Canis Majoris.
They did this on individual regions of the hypergiant, then compared the results to a timeline of mass ejection events from VY Canis Majoris. This step required significant computer processing power. To get the best possible resolution, the team processed nearly a terabyte of ALMA data, with more to come, and detailing each molecule can take up to two days.
“With these observations, we can now put them on sky maps,” Ziurys said. “Until now, only small parts of this huge structure have been studied, but you can’t understand the mass loss and death of these large stars unless you look at the whole region. That’s why we wanted to create a complete picture.”
The team’s findings were presented June 13 at the American Astronomical Society meeting in Pasadena, Calif., and will be detailed in a series of upcoming articles.
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