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Last year, astronomers were surprised when Betelguese, the bright red supergiant star in the constellation Orion, faded dramatically, but then recovered. The eclipse lasted for weeks. Now astronomers have set their sights on a monster star in the adjacent constellation Canis Major, the Big Dog.
The red hypergiant VY Canis Majoris – which is much larger, more massive and more violent than Betelgeuse – experiences much longer, duller periods that last for years. New findings from NASA’s Hubble Space Telescope suggest that the same processes that took place on Betelgeuse are taking place in this hypergiant, but on a much larger scale.
“VY Canis Majoris acts much like Betelgeuse on steroids,” explained the study’s leader, astrophysicist Roberta Humphreys of the University of Minnesota, Minneapolis.
As with Betelgeuse, Hubble data suggests the answer to why this bigger star is fading. For Betelgeuse, the eclipse corresponded to a gas flow that could form dust, which obstructed for us a bit of Betelgeuse’s light, which created the eclipse effect.
“In VY Canis Majoris we see something similar, but on a much larger scale. Massive ejections of material corresponding to its deep fading, which is probably due to dust that temporarily blocks the light from the star,” Humphreys said. .
The enormous red hypergiant is 300,000 times brighter than our sun. If it replaces the sun in our own solar system, the inflated monster will stretch hundreds of millions of miles between the orbits of Jupiter and Saturn.
“This star is absolutely incredible. It’s one of the biggest stars we know of – a very developed, red supergiant. It’s already had a lot of giant eruptions,” Humphreys explained.
Giant plasma arcs surround the star at distances that are thousands of times farther away than the earth is from the sun. These arcs look just like the solar power of our own sun, only on a much larger scale. They are also not physically attached to the star, but appear to have been ejected and moved away. Some of the other structures near the star are still relatively compact and look like small knots and nebulous features.
In previous Hubble work, Humphreys and her team were able to determine when these large structures were being thrown out of the star. They have found dates that vary over the past few hundred years, some as recent as the past 100 to 200 years.
Now, in new work with Hubble, researchers have solved features that are much closer to the star that are less than a century old. By using Hubble to determine the velocities and movements of the nearby hot gas nodes and other features, Humphreys and her team were able to more accurately date these eruptions. What they found was remarkable: many of these knots link to several episodes in the 19th and 20th centuries when VY Canis Majoris faded to a sixth of ordinary brightness.
Unlike Betelgeuse, VY Canis Majoris is now too faint to be seen with the naked eye. The star was once visible, but has faded so much that it can now only be seen with telescopes.
The hypergigantic shed 100 times as much mass as Betelgeuse. The mass in some nodes is more than twice the mass of Jupiter. “It’s amazing that the star can do that,” Humphreys said. “The origin of these large mass loss episodes in both VY Canis Majoris and Betelgeuse is probably caused by large-scale surface activity, large convective cells such as on the sun. But on VY Canis Majoris, the cells can be as large as the entire Sun or larger.”
“It’s probably more common in red giants than scientists thought, and VY Canis Majoris is an extreme example,” Humphreys continued. “It could even be the main mechanism driving the mass loss, which has always been a mystery to red supergiants.”
Although other red supergiants are very bright and emit a lot of dust, none are as complex as VY Canis Majoris. “What’s special about it then? VY Canis Majoris is perhaps in a unique state of evolution that separates it from the other stars. It is probably active over a very short period of time, maybe just a few thousand years. We are not going to see much. of the people around there, ‘Humphreys said.
The star began life as a super hot, brilliant, blue supergiant star, as much as 35 to 40 times our sun’s mass. After several million years, when the rate of burning of hydrogen fusion in its core changed, the star swelled into a red supergiant. Humphreys suspects that the star may briefly return to a warmer state and then swell again to a red giant stage.
“Perhaps what makes VY Canis Majoris so special, so extreme, with this very intricate ejection, could be that it’s a second phase red supergiant,” Humphreys explained. VY Canis Majoris may have already shaken off half of its mass. Instead of exploding like a supernova, it could simply collapse directly into a black hole.
The team’s findings appear in the February 4, 2021 issue of The Astronomical Journal.
The Hubble Space Telescope is a project of international collaboration between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, controls the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts scientific operations of Hubble. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, DC