I have some updates on some news reports that I have been following for some time, both of which caused great uproar when it was first announced: phosphine in the atmosphere of Venus and dust that causes Betelgeuse to fade late 2019 / early 2020.
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You may recall that in September 2020, a team of astronomers announced that they had found evidence of the molecule phosphine in the atmosphere of Venus. Normally this would be a pretty esoteric discovery, but the thing is, you would not find the specific molecule there, as it is fairly easily destroyed in the hellish environment of Venus … and on earth, phosphine is mainly made by anaerobic bacteria . while eating dead things that lived before.
So yeah, kind of a big deal. But then doubts were placed about it, and other scientists said that the data used was not calibrated with the right files, which may make it look like phosphine is seen when it is not actually there. There were some other issues as well.
The original team responded by saying that the detection continues when they use updated calibration files, even though it was weaker. But then things got interesting.
The astronomers who made the original discovery looked at a spectrum and broke up the light of Venus into individual colors. Different molecules absorb light in different colors so that they can be identified. Sometimes, however, molecules absorb very similar, if not overlapping colors, which confuses the problem. A new paper has just come out on this and said that sulfur dioxide (SO2) is incorrect as phosphine as it absorbs light at the same wavelength as phosphine.
This is an interesting argument. Sulfur dioxide is known to exist in the Venusian atmosphere, and they claim (using models of the planet’s atmosphere) that the signature seen in the data can be explained by SO.2 exists in a layer about 80 km above the surface of Venus. It is claimed that phosphine is seen about 50 km higher, but according to the new newspaper, phosphine will be quickly destroyed there.
The argument is compelling and could very well be correct. Phosphine may not be what was seen in the first place. The problem here is that this data was on the edge of what could be seen, so without getting further and deeper observations, the problem could not be solved. I expect that we will soon hear more from the original team about this as well.
As we move from a planet 40 million kilometers away to an inflated star 640 (or possibly 530) light-years away, let’s talk to Betelgeuse.
The iconic star shocked everyone in late 2019 when its brightness dropped like a stone and faded by about 50%. It was easy to notice, and pretty freaky how quickly it faded.
Betelgeuse is a well-known variable star, and its brightness varies by a few percent over a few different cycles. But this deep dive was unprecedented and strange. Astronomers immediately began to devise ideas to explain them. One of them was giant star pots, which apparently were not very likely. Another thing was that the temperature might have dropped. A third, and the one I felt was probably due to support from various sources, is that it sprang up a large cloud of dust that blocked some of its light.
But a new article has just been published that raises the temperature again. Or down, I suppose: they show that part of the upper atmosphere of Betelgeuse could have cooled down considerably, which explained the decline in light.
Stars radiate light because it is hot. As they cool, they fade. Betelgeuse, however, is a red supergiant, a huge bag of gas massive and far, much larger than the sun. The physics of its outer layers are very complex and are not very well understood.
The upper parts of the star expand physically and contract over a period of months to years, making the star brighter and dimmer, and changing the color slightly as well as the temperature. In the new work, the authors show that parts of the upper atmosphere of Betelgeuse have cooled by a few hundred degrees, which explains the eclipse.
They looked at the molecule titanium oxide (TiO), which is commonly seen in very cool stars. It absorbs light at very specific colors in a characteristic way, and what they found is that the absorption by TiO changed when Betelgeuse was dimmer, indicating that it was cooler than previously thought. The exact drop in temperature is difficult to determine, but at some point it shows a clear drop of 150 Kelvins (one degree Celsius = 1 Kelvins). They claim that if the temperature drops by 250 K, no substance is needed at all to explain the eclipse.
This complicates the fact that the constellations of extremely high resolution show that only the southern hemisphere has faded, and it is likely (they argue) that the temperature drop occurred there. If the temperature dropped in only one part of the atmosphere, it would be difficult to find out how much, because the northern hemisphere remained the same and confused the measurement. A drop of 250K is therefore not necessarily unreasonable.
It makes me wonder if there is more than one cause behind the eclipse, both dust and temperature drop. This is not out of the question; when something extreme happens in the universe, it is usually because two or more phenomena are joined together to increase its effect. I’m speculating here, but I certainly would not rule it out.
Funny: Venus is the brightest planet in our sky and the one closest to Earth, and Betelgeuse is one of the brightest stars in the sky and also relatively close as the stars go. But for both, riddles abound.
There are many that we know and understand well about the cosmos in which we live, but there are also many that we do not know, not even about our neighbors next door. And these back-and-forth arguments by scientists about data and cause and physics are normal for science; When we push the boundaries of knowledge, it takes time to figure out what we are seeing. I expect both of these mysteries to be solved to everyone’s satisfaction, and then we move on to the next strange thing that Venus and Betelgeuse will do. This is how the Universe works.