Images reveal changes in Betelgeuse’s shape as it has been dimming

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Betelgeuse dimmed
Click for full image.

Using the Very Large Telescope in Chile astronomers have produced before and after images of the red giant Betelgeuse, showing the changes to the star in the past year as it has dimmed by about 36%.

The image to the right, cropped and reduced to post here, was taken in December and shows the star in its dimmed state. Below the fold is a short video that compares this image with a photograph taken in January 2019. The star was then more spherical and evenly bright.

Betelgeuse’s misshaped profile and uneven brightness is not actually a new thing. See for example this 2017 image, where I noted that the bulge on the star’s side suggested “that continuous observations would reveal the outer atmosphere waxing and waning almost like the stuff inside a lava lamp.” The star is a giant gasbag that in the past has frequently been observed with dark patches on its surface and a sense that it is not always spherical. Those changes however have not occurred with such a significant dimming, a full magnitude

In late December I had posted a story noting that the dimming appeared to be expected, caused by the alignment of two different regular fluctuations of brightness, one 5.9 years long and the other 0.5 year long. It was expected that the star would begin brightening again.

Right now astronomers estimate that the low point in these cycles will occur on approximately February 21st. If the star begins to brighten following that date it would confirm that this dimming is just part of its cycles. If not, then it could be that we are in the preliminaries to a supernova event that would probably make Betelgeuse bright enough to be seen during the day.



  • eddie willers

    I had read about the dimming but didn’t give it much thought. Last week I found myself in the backyard on a clear night and looked up and, Holy Moley, I looked at Orion’s left shoulder and it was noticeably dimmer than I remembered.

    And if these 68 year old eyes could see the difference, it’s real.

    I remember the excitement of 1987A, but if Betelgeuse pops……

  • eddie willers

    I guess I should have said Orion’s left shoulder ‘as we look at it’. From Orion’s view, it is his right shoulder.

  • sippin_bourbon

    I read one article that speculated this could be as a result of a dust cloud moving in front of the star. Not sure what would confirm or deny such a theory.

  • Michael Schnieders

    Sippin_bourbon, unfortunately, dust clouds blocking direct light are difficult to discern. From what I have been able to understand, the only way we could tell if dust is or is not blocking light, is if we had two different types of telescopes observing the same object at the same time; specifically, a visible light (Hubble) and an infrared telescope (James Webb). The reason for this is that certain longer wavelengths (infrared) will pass through the “dust”, while other shorter wavelengths (visible) will be absorbed.
    I am desperately hoping that Betelgeuse will continue along this amazing unpredictable path long enough for the James Web Telescope to come online.

  • sippin_bourbon: I personally think the dust cloud theory is a very unoriginal and pedestrian explanation for an object like this. Red giant stars the size of Betelgeuse are strange things that we have no real direct knowledge of. We have not really seen them, only observed their light from a distance. Their behavior thus is completely unknown, and could easily involve phenomenon that we can’t yet even guess at.

    That the star appears to have changed shape does not surprise me. The data from the better images in the past decade have suggested that it functions kind of like a blob of water in weightlessness, its shape undulating wildly.

    At the same time, we know very little, as the images are poor in resolution and are also widely spaced in time.

  • Jay

    The brightness is changing but has anyone checked the spectroscopy to see if there has been a change or shift in the elements, like less hydrogen?

  • paracelsus

    Not an astronomer, but could this be, rather than the star, other bodies revolving about it; gas giants; a black hole orbiting it at quite a distance?

  • paracelsus: Nope, not in this case. The star itself is undulating in shape, and has large dark spots that periodically cross its face.

  • Surellin

    Hmm, wasn’t aware that Orion was visible from Chile.

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