Sunday, August 7, 2022

VY Canis Majoris Is Dying, and Astronomers Are Watching

Three-dimensional models of celestial objects can be ridiculously complex. They can range from black holes that light doesn’t escape to the literal size of the universe and everything in between. But while not every item has received the necessary attention to develop a complete model of it, we can officially add another overly complex model to our list. Astronomers at the University of Arizona have developed a model of VY Canis Majoris, a red hypergiant that is possibly 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 the subject of some debate recently. Initially, astronomers thought they simply exploded in a supernova, as do many other stars. However, more recent data shows a significant reduction of supernovae compared to the numbers that would be expected if the red hypergiants themselves exploded like that.

The now ongoing theory is that they are more likely to fall into black holes, which are much harder to observe directly than supernovae initially suggested. It is not clear what characteristics of stars that evolve into black holes are, and are to be detected; Modeling would be beneficial.

UT video discusses how big stars can meet.

Enter team from UA. They chose VY Canis Majoris as an excellent stand-in for the type of red hypergiants they were interested in learning more about. The star itself is massive, ranging in size from 10,000 AU to 15,000 AU, which means it will reach 10,000 to 15,000 times more distant from the Sun than Earth is today. And it is only 3,009 light years away from Earth as it is. This makes VY Canis Majoris, which resides in the southern constellation Canis Major, attractive to observers.

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

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

Scalable picture showing how big VY Canis Majoris is compared to our own Sun.
Scalable picture showing how big VY Canis Majoris is compared to our own Sun.
credit – wikipedia user swartkel

UA researchers used the timing on ALMA to collect radio signals of material erupted into space as part of these explosions. That material, which includes sulfur dioxide, silicon dioxide and sodium chloride, would allow him to trace the speed at which it moves, rather than the static presence of other ejecta such as dust. To do this, they had to align all 48 dishes of ALMA and collect more than a terabyte of data to get the correct information.

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It can be quite challenging to process all the data collected, and they are still working on some of it. Still, he had enough time to submit his findings to the American Astronomical Society in mid-June. When they have even more data, they will be able to describe an even better model of what one of the galaxy’s most massive stars looks like. And someday, in the future, there may be a chance to test the model of what will happen to the red hypergiant when the 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 1 mm spectral line surveys
UT – VY Canis Major is “Like Betelgeuse on Steroids”
UT – Hubble sees a hypergiant star nearing death

Lead Image:
Artist’s illustration of V Y Canis Majoris
credit – NASA / ESA / Hubble / R. Humphries, University of Minnesota / J.J. Olmsted, STSCI.

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