New photo of a star that people hope will explode shows it fading and changing shape

Betelgeuse just keeps getting weirder and weirder.

The massive star has been the subject of much discussion over the past few months after it began to dim in December. The fading hasn't stopped, and the star that usually lies in the top 10 brightest has fallen to 24th. 

Then, last month, a gravitational wave was detected from the region. These ripples of space-time can occur by massive objects merging, like two black holes or two neutron stars.

Now, astronomers using the European Southern Observatory's Very Large Telescope have photographed the massive star and revealed that it appears to have changed shape.

The team has been observing Betelgeuse for some time and, in fact, had taken an image in January 2019 using the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument on the telescope (SPHERE). 

But their followup photograph in December — released today — showed something entirely different.

"We imaged [Betelgeuse] last year … and at that time it wasn't dimming," said Emily Cannon, an astronomer at the Institute of Astronomy, KU Leuven in Belgium. "After we got that [new] image we realized that there's actually quite a large difference between the two of them. So now it's, 'What is causing that?'"

Swipe to compare 2019 images from January and December:

For one, the star has changed shape. Also in the image is a bright spot near the top left, and of course, the dimming seen at the lower part of the star.

"It looks like half of the star is hidden behind, in a sense, a sort of curtain," said Pierre Kervella, an astronomer with LESIA at the Observatoire de Paris — PSL, who was also involved in acquiring the photograph.

Though Kervella said they're still collecting observations, he said that one hypothesis is that the star has ejected material that has condensed into molecules and dust grains which resemble a "cloud of smoke."

Seeing as Betelgeuse is 14,000 times more luminous than our sun (it's also massive: roughly 1,400 times larger than our sun), it would take an immense amount of material for this to occur. But Kervella said that's another thing they're trying to determine.

ESO, IAU and Sky & Telescope

The bright spot, astronomers believe, is caused by convective cells. These are regions where hotter material is rising to the star's surface while cooler material goes down. Our sun has millions of these cells, whereas it's believed that a red supergiant like Betelgeuse likely just has five or 10.

Cannon notes that red supergiants don't actually appear round, as big bubbles of gas can be bubbling out in various directions, so that could account for the star's strange appearance.

A big 'boom'?

Red supergiants are some of the most massive and brightest stars, but they don't live that long. In human terms, Betelgeuse is a geriatric at 10 million years old, because red supergiants go through their fuel so quickly. It is nearing the end of its life. By contrast, our smaller sun is roughly 4.5 billion years old, but, as a yellow dwarf, is considered just middle-aged.

Red supergiant stars like Betelgeuse die in a spectacular fashion: after exhausting all their hydrogen and helium they collapse onto themselves, and finally explode in a supernova, one of the most cataclysmic events in the universe. And Betelgeuse is near the end of its life. 

ESO/L. Calçada

Betelgeuse is a semi-regular variable star, meaning that it dims periodically, with multiple periods. It has cycles of roughly 430 days, but also 100 to 180 days as well as one of about six years.

But now Betelgeuse is at 36 per cent its normal brightness. And some people think all this activity — the deep minimum, the potential gravitational wave and now its seemingly misshapen appearance — might mean it's going to go boom.

Due to its proximity, if it did go supernova, astronomers believe it would be as bright as the full moon and visible during the day.

"This is something everyone would like to see," said Kervella. "If it would explode, it would be a marvellous show."

However, he added, "I'd say it's quite unlikely in terms of pure statistics that we'll see it in our lifetime." 

Though Cannon said she doesn't believe what they've observed means that Betelgeuse is necessarily ready to pop now, she added that our knowledge on red supergiants is somewhat limited.

"Never say never, because we don't really know that much about what's going on with red supergiants," she said. "It's impossible to rule out anything, really."