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Hubble Telescope Solves Mystery Of Star’s Dimming



Images of massive red hypergiant VY Canis Majoris provided astronomers with answers.

New findings from NASA’s Hubble Space Telescope have helped astronomers to solve the mystery of why Orion’s bright red supergiant Betelgeuse dramatically faded for a period of weeks last year. 

In examining the massive red hypergiant VY Canis Majoris, astrophysicists from NASA and the University of Minnesota, Minneapolis found that the same processes are occurring on a much larger scale.

The observation was published in the Feb. 4, 2021 edition of The Astronomical Journal, where the authors wrote that imaging and spectroscopy confirm a “record of high mass-loss events over the past few hundred years.”

“The similarity of this correspondence in VY [Canis Majoris] with the remarkable recent dimming of Betelgeuse and an outflow of gas is apparent,” they said. “The evidence for similar outflows from the surface of a more typical red supergiant suggests that discrete ejections are more common and surface or convective activity is a major source of mass loss for red supergiants.”

In a Thursday press release from NASA, the University of Minnesota’s Distinguished Professor Roberta Humphreys explained that Hubble data showed VY Canis Majoris behaving like Betelgeuse “on steroids.” 

In the case of the smaller star, researchers say that the dimming was due to an outflow of gas that may have formed dust which temporarily obstructed some of the star’s light. 

“I think the big takeaway about these results, is that the massive ejections or outflows from the star observed in the [Hubble] images and measured in the spectra are correlated with periods of great variability and deep minima in its light observed over two centuries,” Humphreys said on Friday. 

“We think this is due to activity or convection on the surface responsible for massive gaseous ejections,” she continued. “For example, we know that the sun has flares and outburst of flows of gas we see as prominences.”

“In VY Canis Majoris — 30 [times the] mass of [the] sun and 300,000 more luminous — this is much more extreme,” she said. “These gaseous outflows may be as much as 10 times the mass of Jupiter.”

Arcs of plasma surround VY Canis Majoris, appearing to have been cast out from it by distances that are thousands of times farther away than the Earth is from the sun and over the past several hundred years.

However, other structures close to the millions of years-old star — which look like knots — are relatively compact and scientists working with Humphrey were able to date more recent eruptions to the 19th and 20th centuries when VY Canis Majoris faded to one-sixth of its original brightness.

The release notes that the hypergiant loses 100 times as much mass at Betelgeuse and is now only visible using a telescope.

“This is probably more common in red supergiants than scientists thought and VY Canis Majoris is an extreme example,” she said in the release. “It may even be the main mechanism that’s driving the mass loss, which has always been a bit of a mystery for red supergiants.”

The future of the start is uncertain, but Humphreys said that the star is “obviously unstable.”

“This high mass loss will determine its eventual fate either as a supernova or black hole,” she said.

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