Artist’s impression of the purple hypergiant star VY Canis Majoris. Located about 3,009 light-years from Earth, VY Canis Majoris is probably the most huge star in the Milky Way. Credit: NASA / ESA / Hubble / R. Humphreys, University of Minnesota / J. Olmsted, STScI / hubblesite.org

By tracing molecular emissions in the outflows round the purple hypergiant star VY Canis Majoris, astronomers have obtained the first detailed map of the star’s envelope, which sheds gentle on the mechanisms concerned in the ultimate phases of excessive supergiant star.

A University of Arizona-led group of astronomers has created a detailed, three-dimensional picture of a dying hypergiant star. The group, led by UArizona researchers Ambesh Singh and Lucy Ziurys, traced the distribution, instructions, and velocities of a selection of molecules surrounding a purple hypergiant star often known as VY Canis Majoris.

Their findings, which they offered on June 13, 2022, at the 240th Meeting of the American Astronomical Society in Pasadena, California, supply insights, at an unprecedented scale, into the processes that accompany the loss of life of big stars. The work was finished with collaborators Robert Humphreys from the University of Minnesota and Anita Richards from the University of Manchester in the United Kingdom.

Extreme supergiant stars often known as hypergiants are very uncommon, with solely a few recognized to exist in the Milky Way. Examples embody Betelgeuse, the second brightest star in the constellation Orion, and NML Cygni, also referred to as V1489 Cygni, in the constellation Cygnus. Unlike stars with decrease lots – which usually tend to puff up as soon as they enter the purple big section however typically retain a spherical form – hypergiants are likely to expertise substantial, sporadic mass loss occasions that kind complicated, extremely irregular constructions composed of arcs, clumps, and knots.

Located about 3,009 light-years from Earth, VY Canis Majoris – or VY CMa, for brief – is a pulsating variable star in the barely southern constellation of Canis Major. Spanning wherever from 10,000 to 15,000 astronomical items (with 1 AU being the common distance between Earth and the solar) VY CMa is probably the most huge star in the Milky Way, in accordance with Ziurys.

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

The group selected to check VY CMa as a result of it’s one of the finest examples of these sorts of stars.

“We are particularly interested in what hypergiant stars do at end of their lives,” mentioned Singh, a fourth-year doctoral pupil 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 NASA’s Hubble Space Telescope and spectroscopy confirmed the presence of distinct arcs and different clumps and knots, many extending 1000’s of AU from the central star. To uncover extra particulars of the processes by which hypergiant stars finish their lives, the group got down to hint sure molecules round the hypergiant and map them to preexisting pictures of the mud, taken by the Hubble Space Telescope.

“Nobody has been able to make a complete image of this star,” Ziurys mentioned, explaining that her group got down to perceive the mechanisms by which the star sheds mass, which look like totally different from these of smaller stars getting into their purple big section at the finish of their lives.

“You don’t see this nice, symmetrical mass loss, but rather convection cells that blow through the star’s photosphere like giant bullets and eject mass in different directions,” Ziurys mentioned. “These are analogous to the coronal arcs seen in the sun, but a billion times larger.”

The group used the Atacama Large Millimeter Array, or ALMA, in Chile to hint a selection of molecules in materials ejected from the stellar floor. While some observations are nonetheless in progress, preliminary maps of sulfur oxide, sulfur dioxide, silicon oxide, phosphorous oxide and sodium chloride had been obtained. From these information, the group constructed a picture of the world molecular outflow construction of VY CMa on scales that encompassed all ejected materials from the star.

“The molecules trace the arcs in the envelope, which tells us molecules and dust are well-mixed,” Singh mentioned. “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 transferring ALMA’s 48 radio dishes into totally different configurations, the researchers had been capable of receive details about the instructions and velocities of the molecules and map them throughout the totally different areas of the hypergiant’s envelope in appreciable element, even correlating them to totally different mass ejection occasions over time.

Processing the information required some heavy lifting in phrases of computing energy, Singh mentioned.

“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 mentioned. “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 mentioned. “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 group plans to publish its findings in a collection of papers.

Meeting: 240th assembly of the American Astronomical Society





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