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astronomy, betelgeuse

Clues from Distant Betelgeuse

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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.

The red supergiant star Betelgeuse, in the constellation of Orion, has been undergoing unprecedented dimming. This stunning image of the star’s surface, taken with the SPHERE instrument on ESO’s Very Large Telescope late last year, is among the first observations to come out of an observing campaign aimed at understanding why the star is becoming fainter. When compared with the image taken in January 2019, it shows how much the star has faded and how its apparent shape has changed. Credit:
ESO/M. Montargès et al.)

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.

This image, obtained with the VISIR instrument on ESO’s Very Large Telescope, shows the infrared light being emitted by the dust surrounding Betelgeuse in December 2019. The clouds of dust, which resemble flames in this dramatic image, are formed when the star sheds its material back into space. The black disc obscures the star’s center and much of its surroundings, which are very bright and must be masked to allow the fainter dust plumes to be seen. The orange dot in the middle is the SPHERE image of Betelgeuse’s surface, which has a size close to that of Jupiter’s orbit. Credit: ESO/P. Kervella/M. Montargès et al., Acknowledgement: Eric Pantin)

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.

astronomy, solar physics, solar studies, sun

The Boiling Sun

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Living with a star, our Sun, is something we do every day. Of course, most of us just bask in the sunlight when it’s available. But, for solar physicists, the astronomers who study the Sun, our star presents a great opportunity to delve deeper into what makes it tick. Or, in the case of some recently released images and vids, what makes it look like a boiling Sun.

The Daniel K. Inouye Solar Telescope on the Hawaiian island of Maui is the latest giant telescope to turn its high-resolution instruments to look at our Sun. The video below shows a view of the Sun that we’d never see if we were to travel to it. But, the telescope is sensitive to light beyond the spectrum that we can see (which is a range between 400 and 700 nanometers). This view is of light that radiates at 705 nanometers, so just beyond what we can see.

Why a Boiling Sun?

What’s happening here? Well, we know the Sun is hot at its core, where it’s more than 15 million degrees! That heat travels out from the center and is released at the surface, called the chromosphere. There, we see a turbulent motion in the gases that make up the Sun’s atmosphere. That action is what makes it look like a boiling Sun in the video.

Those cells of superhot gases are a cooling mechanism. They bring the heat up from beneath the solar surface and then release it. It’s the way our star sends heat out to the rest of the solar system. Watch the video for a short bit and it might remind you of boiling fudge, or syrup on the stove. Those also operate under the same principle of heat “release”.

On the Sun, the heat rises up from this region into space through the outer layers of the Sun’s atmosphere. Temperatures there are about 6,000 C (10,800 F). A funny thing happens above the surface—the heat steadily rises until it’s more than a million degrees in the uppermost region called the corona. Solar scientists are busily figuring out why this superheating happens, and they know that solar magnetic fields are somehow involved.

The interesting thing about this video (and the images from DIST) is that these are the sharpest images of the boiling surface of the Sun ever taken. And, they were taken from Earth! Want to know more about this telescope and see additional images? Check out their website here.