VY Canis Majoris is Enshrouded in Giant Dust Clouds, Astronomers Say | Astronomy

Astronomers using the NASA/ESA Hubble Space Telescope have discovered the reason for the dimming of a red hypergiant star called VY Canis Majoris.

This artist’s impression of the red hypergiant VY Canis Majoris shows the star’s vast convection cells and violent ejections. Image credit: NASA / ESA / Hubble / R. Humphreys, University of Minnesota / J. Olmsted, STScI.

VY Canis Majoris is located 3,840 light-years away in the constellation of Canis Major.

Also known as VY CMa, HD 58061 or HIP 35793, VY Canis Majoris, the star is about 1,420 times larger, 35 times more massive, and 300,000 times more luminous than the Sun.

If it replaced the Sun in our Solar System, VY Canis Majoris would extend out for hundreds of millions km, between the orbits of Jupiter and Saturn.

“VY Canis Majoris is behaving a lot like Betelgeuse on steroids,” said Professor Roberta Humphreys, an astrophysicist in the Minnesota Institute for Astrophysics at the University of Minnesota.

“As with Betelgeuse, Hubble data suggest the answer for why this bigger star is dimming.”

“For Betelgeuse, the dimming corresponded to a gaseous outflow that may have formed dust, which briefly obstructed some of Betelgeuse’s light from our view, creating the dimming effect.

“In VY Canis Majoris we see something similar, but on a much larger scale. Massive ejections of material which correspond to its very deep fading, which is probably due to dust that temporarily blocks light from the star.”

This Hubble image shows the huge nebula of material cast off by VY Canis Majoris. Image credit: NASA / ESA / Hubble / R. Humphreys, University of Minnesota / J. Olmsted, STScI.

In a previous study, Professor Humphreys and colleagues determined when these large structures were ejected from the star.

They found dates ranging over the past several hundred years, some as recently as the past 100 to 200 years.

In a new study, they resolved features much closer to the star that may be less than a century old.

By using Hubble to determine the velocities and motions of the close-in knots of hot gas and other features, they were able to date these eruptions more accurately.

What they found was remarkable: many of these knots link to multiple episodes in the 19th and 20th centuries when VY Canis Majoris faded to one-sixth its usual brightness.

Unlike Betelgeuse, VY Canis Majoris is now too faint to be seen by the naked eye. The star was once visible but has dimmed so much that it can now only be seen with telescopes.

“So what’s special about it? VY Canis Majoris may be in a unique evolutionary state that separates it from the other stars,” Professor Humphreys said.

“It’s probably this active over a very short period, maybe only a few thousand years. We’re not going to see many of those around.”

VY Canis Majoris began life as a super-hot, brilliant, blue supergiant star perhaps as much as 35 to 40 times our Sun’s mass.

After a few million years, as the hydrogen fusion burning rate in its core changed, the star swelled up to a red supergiant.

The researchers suspect that the star may have briefly returned to a hotter state and then swelled back up to a red supergiant stage.

“Maybe what makes VY Canis Majoris so special, so extreme, with these very complex ejecta, might be that it’s a second-stage red supergiant,” Professor Humphreys said.

“VY Canis Majoris may have already shed half of its mass. Rather than exploding as a supernova, it might simply collapse directly to a black hole.”

The study was published in the Astronomical Journal.

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Roberta M. Humphreys et al. 2021. The Mass-loss History of the Red Hypergiant VY CMa. AJ 161, 98; doi: 10.3847/1538-3881/abd316