Scientists watch as the galaxy’s largest star dies

Scientists watch as the galaxy’s largest star dies

The Red Hypergiant VY Canis Majoris (NASA/ESA/Hubble/R. Humphreys, University of Minnesota/J. Olmsted, STScI/hubblesite.org)

The Red Hypergiant VY Canis Majoris (NASA/ESA/Hubble/R. Humphreys, University of Minnesota/J. Olmsted, STScI/hubblesite.org)

Scientists now have the most detailed image yet of a dying giant: VY Canis Majoris, likely the largest star in our galaxy.

VY Canis Majoris is a red hypergiant, a class of stars so massive they can be 10,000 times the distance between Earth and Sun in diameter, and little is known about their last stages of life. Rather than ballooning into a large red ball like most red giant stars, hypergiants swell into erratic tumults of arcs and protrusions, and go through phases in which they eject large amounts of mass.

Now an international team led by University of Arizona researchers has traced the arcs and mass outbursts of VY Canis Majoris, providing the clearest image yet of a hypergiant star’s death spasms. The team’s results were announced on June 13 at the 240thth Meeting of the American Astronomical Society in Pasadena, California.

“We’re particularly interested in what hypergiant stars do at the end of their lives,” Ambesh Singh, a chemistry doctoral student at the University of Arizona, said in a statement about the work. “People used to think these massive stars just evolve into supernovae explosions, but we’re not so sure anymore.”

There are only a handful of hypergiants in our galaxy, and the second brightest star in the constellation of Orion, Betelgeuse, is perhaps the best known. But VY Canis Majoris, located about 3,000 light-years from Earth in the southern constellation of Canis Major, is the largest of the greats.

“Think of it as Betelgeuse on steroids,” Lucy Ziurys, a professor of chemistry at the University of Arizona, said in a statement. “It’s much larger, much more massive, and experiences violent mass eruptions about every 200 years.”

To better understand these eruptions and the domed and knotted shape of VY Canis Majoris, Drs. Ziurys and Mr. Singh used the Atacama Large Millimeter Array, or ALMA, a radio telescope in Chile to detect specific molecules in the material ejected from the hypergiant star. They then matched these traces to VY Canis Majoris images previously taken by the Hubble Space Telescope to create maps of sulfur oxide, sulfur dioxide, silicon oxide, phosphorus oxide and sodium chloride in material ejected from the star.

“With these observations, we can now plot them on maps in the sky,” said Dr. Ziurys in a statement. “Only small parts of this enormous structure have been studied so far, but you can’t understand the mass loss and how these big stars are dying unless you look at the entire region.” So we wanted to create an overall picture.”

The new image could help scientists better understand where in the sky supernovae explosions are no longer visible. Although they’re rare in our galaxy, hypergiants are plentiful throughout the cosmos, and their fiery deaths should be visible if that’s the typical way they end their lives, said Dr. Ziurys.

“We now think that they might silently collapse into black holes,” she said, “but we don’t know which ones end their lives that way or why that happens and how.”

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