Clues from Distant Betelgeuse

A few weeks ago I wrote about the “Betelgeuse problem” which asks the question: why is it dimming? A lot of people are really in love with the idea that it’s going to blow up soon. I have to admit, it’s a fascinating thought, that we would get to see a giant star blow itself to smithereens from a safe distance of about 700 hundred light-years. But, it’s probably not what’s going to happen. At least, not just yet.

Taking a Direct Look at Betelgeuse

Figuring out exactly what IS happening with this star is complex. We know it’s an old star. Those aged, dying supergiants get a little eccentric in their final epochs of life. Astronomers have a general idea of what’s going on inside Betelgeuse, but that doesn’t explain why its appearance is changing. It could be due to some kind of stellar activity affecting its appearance and apparent size and shape. Could the surface be cooling for some reason? If so, what would explain that?

Another idea is that the star is ejecting dust away from itself. It ends up as clouds in the line of sight between us and the star. Such clouds could affect the star’s appearance pretty drastically. They would also absorb some of the light, which makes it look dimmer.

To figure this out, we need direct images of the star. So, astronomers used the Very Large Telescope in Chile to look directly at the star. They deployed special instruments to get a direct view of its surface in visible light as well as infrared light. Of course, Betelgeuse, like the Sun, is a massive ball of superhot gas. So, there’s not really a surface like we have on Earth. On the Sun, the “surface” is the “photosphere”. We can “see” all the way through the solar atmosphere to that region, and below that, we can’t see because it’s opaque to visible light.

December’s View of Betelgeuse

The “surface” on Betelgeuse is a similar region. The VLT showed astronomers the surface, and also let them study the material surrounding the star. That cloud of “star stuff” has been ejected from Betelgeuse in its later life. The December images of Betelgeuse show it not as a rounded sphere of hot gas, but a somewhat squished-looking thing. The infrared images of the dust look even stranger, showing clumps of star-stuff nearby the star.

That image of dust around Betelgeuse may be providing an important clue to understanding the dimming we’re seeing at the star. It could well be that those dust clouds are playing a role in blocking light from the star. That could be why it appears to be getting dimmer.

Betelgeuse’s Future

The ejection of dust from older (and dying) stars, called “mass loss”, is one part of Betelgeuse’s aging process. It’s actually part of what many stars experience. The Sun itself will go through a period of mass loss as it ages, and will gently blow its atmosphere out to space. In the case of Betelgeuse, it may go through several epochs of mass loss. Eventually, it could end up with several surrounding shells of gas and dust. When it does go through the final collapse (in perhaps 100,000 to a million years), the outbursting material from the torn-apart star will encounter those shells. It’ll heat them up, cause them to sparkle and glow, and make the death of Betelgeuse quite spectacular.

But, for now, if the images from VLT are to be believed, we’re still in for some episodes of mass loss. They’ll continue as Betelgeuse makes its way through old age. It’s actually pretty cool that astronomers can capture views of the star at this point. What they see gives a much better idea of the things that happen to supergiant stars before they explode as Type IIa supernovae and light up our night sky.

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