Tag Archives: Betelgeuse

Betelgeuse dimming caused by outburst

The uncertainty of science: According to new data from the Hubble Space Telescope, astronomers are now proposing that the dimming seen earlier this year in the red giant Betelgeuse was caused not by a known variation cycle or by a large starspot moving across its surface, but by an large outburst of material, thrown out from the star.

Ultraviolet observations by the Hubble Space Telescope suggest that the unexpected dimming was probably caused by an immense amount of superhot material ejected into space. The material cooled and formed a dust cloud that blocked the starlight coming from about a quarter of Betelgeuse’s surface.

That we now have three creditable but different theories, all based on evidence, for explaining the dimming that occurred from October 2019 to April 2020 suggests that we really still have no idea what specifically caused it. All three theories however are based on what we do know about Betelgeuse, that it is giant blobby gasbag that has dark starspots on its surface, that has giant convection cells that bubble up from below and release material periodically, and that it pulses in a variety of cycles predictably over time.

It could be any of these phenomenon that caused last year’s dimming, or even a combination of two or more. The information available so far is just too sketchy to pin this down more precisely.

Giant dark starspots explain Betelgeuse’s dimming last year

Astronomers now think that unusually large dark starspots on the face of the red supergiant star Betelgeuse caused its dimming from October 2019 to April 2020.

“Corresponding high-resolution images of Betelgeuse from December 2019 show areas of varying brightness. Together with our result, this is a clear indication of huge star spots covering between 50% and 70% of the visible surface and having a lower temperature than the brighter photosphere,” said co-author Peter Scicluna from the European Southern Observatory (Eso).

“For comparison, a typical sunspot is the size of the Earth. The Betelgeuse star spot would be a hundred times larger than the Sun. The sudden fading of Betelgeuse does not mean it is going supernova. It is a supergiant star growing a super-sized star spot.” said co-author Prof Albert Zijlstra from The University of Manchester, UK

Starspots have been identified on the surface of Betelgeuse previously, so what is interesting here is how large these spots were.

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

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.
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Astronomers take best image of Betelgeuse yet

Betelqeuse

Using the Atacama Large Millimeter/submillimeter Array Telescope (ALMA), astronomers have produced the best picture of the red giant star Betelgeuse taken so far.

Using ESO’s Very Large Telescope astronomers discovered a vast plume of gas almost as large as our Solar System. Astronomers have also found a gigantic bubble that boils away on Betelgeuse’s surface. These features help to explain how the star is shedding gas and dust at tremendous rates (eso0927, eso1121). In this picture, ALMA observes the hot gas of the lower chromosphere of Betelgeuse at sub-millimeter wavelengths — where localised increased temperatures explain why it is not symmetric.

The image on the right is that image, slightly reduced to post here. The bulge on the star’s left illustrates the unevenness of the star’s upper atmosphere. I suspect that continuous observations would reveal the outer atmosphere waxing and waning almost like the stuff inside a lava lamp.

Betelgeuse might have eaten a star

Because the red giant star Betelgeuse rotates far faster than it should, astronomers are now theorizing that when it expanded into its present red giant phase about 100,000 years ago it swallowed a companion star which contributed its own angular momentum to the system to speed up the rotation.

This theory is bolstered by evidence of a shell of matter surrounding Betelgeuse that is possibly a remnant of that destroyed star.

Betelgeuse baffles astronomers

The uncertainty of science: New data of the red giant star Betelgeuse says that the star simply doesn’t have the energy to eject the large amount of gas it routinely blows into space.

“[W]e now have a problem”, says Graham Harper, an astrophysicist at the University of Colorado Boulder. “If you’re going to eject matter you have to put energy in, and we’re not seeing that.” Harper and his colleagues used the US–German Stratospheric Observatory for Infrared Astronomy (SOFIA), a 2.5-metre telescope that flies in a modified Boeing 747 aeroplane, to take Betelgeuse’s temperature. They found that the star’s upper atmosphere was much cooler than expected — so cool, in fact, that it doesn’t seem to have enough energy to kick gas out of its gravitational pull and into space.

“This challenges all our theoretical models,” Harper said on 7 January at a meeting of the American Astronomical Society in Kissimmee, Florida. [emphasis mine]

The data suggests the temperature of the ejected gas to be only about 512 degrees Fahrenheit. This is far too cool to fit any theory for explaining the vast amounts of gas that the star routinely puffs into space. It also suggests, not surprisingly, that scientists do not yet have a enough information to develop a clear understanding of stellar evolution. They have enough information to form rough theories, but there is still much too much they do not know.

A new infrared image of Betelgeuse suggests the star and its winds will smash into the interstellar medium in only a few thousand years.

Crash! Boom! A new infrared image of Betelgeuse suggests the star and its winds will smash into the interstellar medium in only a few thousand years.

If the bar [of gas] is a completely separate object, then taking into account the motion of Betelgeuse and its arcs and the separation between them and the bar, the [star’s] outermost arc will collide with the bar in just 5000 years, with the red supergiant star itself hitting the bar roughly 12 500 years later.

Want to see an asteroid eclipse a star?

transit of Betelgeuse

On January 2, 2012, an asteroid is going to transit across the face of Betelgeuse. And if you live in Europe, own a very sensitive telescope, look close and don’t blink, you might be able to see it!

This is all according to a preprint paper published today on the Los Alamos astro-ph preprint website, written by scientist Costantino Sigismondi of the Galileo Ferraris Institute and International Center for Relativistic Astrophysics in Rome. You can download the paper here [pdf].

The transit itself will only last 3.6 seconds, and will only be visible along a narrow swath crossing southern India and moving across the Middle East, through parts of Italy, France, and the southwestern most tips of England and Ireland. A map of this path is below the fold.
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