VY Canis Majoris dies and astronomers watch

Three-dimensional models of astronomical objects can be ridiculously complex. They can range from black holes that light can’t even escape to, to the literal size of the universe and everything in between. But not every object has received the attention needed to develop a complete model of it, but we can officially add another very complex model to our lists. Astronomers at the University of Arizona have developed a model of VY Canis Majoris, a red hypergiant that may be the largest star in the Milky Way. And they’re going to use that model to predict how it will die.

How red hypergiants die has been a topic of debate lately. At first, astronomers thought they just exploded in a supernova, like so many other stars do. However, more recent data shows a significant lack of supernovae compared to the numbers expected if red hypergiants themselves exploded that way.

The prevailing theory now is that they are more likely to collapse into a black hole, which is much more difficult to observe directly than the initially suggested supernovae. It remains unclear what exactly are the characteristics of the stars that would evolve into black holes, and to find out; it would be helpful to have a model.

UT video discussing how big stars can become.

Enter UA’s team. They chose VY Canis Majoris as an excellent stand-in for the type of red hypergiants they wanted to learn more about. The star itself is huge, ranging from 10,000 AU to 15,000 AU in size, meaning it would extend 10,000 to 15,000 times further away than Earth is from the sun today. And it’s only 3,009 light-years from Earth as it is. This makes VY Canis Majoris, located in the southern constellation of Canis Major, fascinating to observers.

Its sheer size and proximity to our solar system make it an excellent observation candidate. With good observational data, astronomers can see the breathtaking complexity of what the star’s surface actually looks like.

One of the fundamental processes in the death of a star is mass loss. This usually happens when gas and dust are evenly blown out of the star’s photosphere. However, on VY Canis Majoris, there are huge features similar to Earth’s coronal arcs, but a billion times more massive.

Scalable image showing how large VY Canis Majoris is compared to our own sun.
Scalable image showing how large VY Canis Majoris is compared to our own sun.
Credit – Wikipedia user Svartkell

The UA researchers used time on ALMA to collect radio signals from the material blown into space as part of these eruptions. That material, including sulfur dioxide, silicon dioxide and sodium chloride, would allow them to detect the speed at which it moves, rather than just the static presence of other ejecta, such as dust. To do this, they had to align all 48 ALMA dishes and collect more than a terabyte of data to get the correct information.

Processing all that collected data can be quite challenging, and they are still working on some of it. Still, so far, they had enough to present their findings to the American Astronomical Society in mid-June. If they have even more data, they can describe an even better model of what one of the largest stars in the galaxy looks like. And someday, far in the future, that model of what will happen to a red hypergiant might get a chance to be tested when VY Canis Majoris finally, officially, dies.

Learn more:
UA- Watching the Death of a Rare Giant Star
Singh et al- Molecules and outflows in NML Cygni: new insights from a 1 mm . spectral line study
UT- VY Canis Majoris Is “Like Betelgeuse On Steroids”
UT- Hubble sees a hypergiant star almost dead

Lead image:
Artist image of VY Canis Majoris
Credit – NASA/ESA/Hubble/R. Humphreys, University of Minnesota/J. Olmsted, STScI.

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