UPDATE: I forgot to provide the link to the article this came from. Here it is.
Betelgeuse is one of the best-known stars in the night sky. It is the sixth brightest star in the Earth’s sky, found in the constellation Orion, where it demarcates the hunter’s left shoulder. It is a red supergiant, 15-20 times the mass of our sun, and 750-1000 times its diameter. (If Betelgeuse were at the center of the Solar System, it would engulf the orbits of all the inner planets, through Mars.)
Supergiant stars have much shorter lives (say, about 10 million years) than those of less massive stars like our sun (about 10 billion years), because the supergiants use up their hydrogen fuel much more quickly. Red supergiants, like Betelgeuse, are in the last stage of their lives. In the production of heat and light, supergiant stars use their fuel hydrogen to produce many other elements: carbon, nitrogen, oxygen, and other elements up through iron. These elements can make up the substance of planets, and the stuff of life. When the fuel runs out, there is no longer a force keeping the mass of the star from collapsing, and so the star supernovas. The explosion then disperses the elements the star has produced throughout the galaxy, where they may condense to form rocky planets, and perhaps life. Indeed, this process is where the elements that make up our own bodies came from. In principle, Betelgeuse could supernova at anytime, but astrophysicists predict the interval of “anytime” spans the next 200,000 years.
Last year around this time, Betelgeuse started acting funny. The star dimmed dramatically and unexpectedly, and astronomers and astrophysicists struggled to figure out why. Immediately, there was speculation that Betelgeuse might be getting ready to supernova. Starting in October 2019, the star’s brightness steadily decreased until it reached a minimum in early February 2020. After that, the star’s brightness recovered to previous levels over the next two months, and things seemed to return to normal.
So what the heck happened? Potential explanations are found over the fold, as well as the day’s comments, but first, we bring you this message from our sponsor:
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It should be noted before proceeding that Betelgeuse has well-established brightness cycles. Indeed, the first of these, lasting about 400 days, was discovered by British astronomer John Herschel in 1839. This particular cycle is a convectional one, where hot material from the interior of the star rises to the its surface, causing it to brighten, and then it dims as the material cools, until the cycle starts over again, where the cold material falls while more hot material rises to replace it. In addition to this cycle, there is a 6-year cycles whose cause is not as well established as the shorter one. The dimming that was observed from the star late last year was well outside the bounds established from 180 years of brightness observations, which signaled that something unique was happening.
Measured brightness of Betelgeuse between September 2018 and April 2020. (A.K. DUPREE ET AL/ASTROPHYSICAL JOURNAL 2020)
While speculation of a potential supernova was running through the popular science press, most astronomers and astrophysicists were seeking another explanation. One was that, in the course of it’s regular convectional cycle, the star had belched a significant amount of its product stardust—those heavier elements it was producing. as the spewed elements cooled, they formed a dust cloud that blocked the star’s light, making it appear dimmer. Betelgeuse is surrounded by dust clouds (as shown in the image at the top of the diary), so it’s entirely possible that perhaps a bit more matter than usual was expelled, and the resulting cloud blocked the star’s light. This could also explain the fact that the distribution of emitted light from the star was not evenly distributed. In the image below, taken during December of 2019, you can see that the lower portion of the image is dimmer than the upper portion. In this interpretation, the dimmer portion of the image corresponds to the principal location of the dust cloud. Once the cloud dispersed, the star returned to its usual brightness. If this hypothesis is correct, it would mean that red supergiants are capable of expelling the elements of life well before they explode.
Image of Betelgeuse from December of 2019, showing dimming on approximately half of the star. (ESO, M. MONTARGÈS ET AL)
However, there isn’t universal agreement for this hypothesis because it is at odds with other observations, in particular with measurements of light outside the visible portion of the spectrum. For example, in the sub-milimeter portion (with wavelengths longer than visible light), the scattering of this light off the dust particles ought to have caused the star to brighten, but it did not. This observation gave rise to two other hypotheses as alternatives to the dust cloud. First, it may be that there was a rare coincidence of all of the brightness cycles of the star (400 days, 6 years, and a more recently identified 187 day cycle) to a dimness not seen before. Second, it may have been an enormous starspot (a star’s equivalent of a sunspot, the magnetic storms observed on the Sun). Because the dynamics of supergiant stars are not well understood, and given how far away they are, they are difficult to study, so it is not known how feasible these alternative explanations might be. In fact, the correct explanation might lie in some combination of these hypotheses. In any case, observation of Betelgeuse ceased when telescopes closed their operations in March as a response to the coronavirus pandemic.
So Betelgeuse unexpectedly dimmed, didn’t explode, and returned to normal brightness after a few months. There are some interesting theories to explain the dimming, including involvement of a dust cloud, but nothing is certain. Hopefully, this observation will help us to learn about the behavior of red supergiant stars in general.
Now to the comments:
Top Comments (December 5, 2020):
From Puddytat:
wxo posts a diary-worthy comment on RW extremism. What is observed locally is a nationwide phenomenon which explains why they are so fervent. From HalBrown’s post on developments in Oregon.
From SottoVoce:
livosh1 posted this comment in Jessica Sutherland’s post on Trump demanding the names of GOP Congresspeople who say he lost the election.
What a different Republican Party than what we had during Watergate, when virtually the entire leadership and membership decided enough was enough and sent Barry Goldwater to the White House to deliver the message to Nixon that it was over and he had to go.
We don’t have a two-party system when one party does not stand for democracy, the rule of law, and the peaceful transfer of power. Today’s Republican Party is shameful, unprincipled, and an evil piece of shit.
Top Mojo (December 4, 2020):
Top Mojo is courtesy of mik! Click here for more on how Top Mojo works.
Top Photos (December 4, 2020):
Thanks jotter!
