I have a couple of updates on some news I’ve been following for quite some time, both of which caused quite a stir when it was first announced: phosphine in Venus ’atmosphere and dust that caused Betelgeuse’s decline in late 2019 / early 2020.
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Recall that in September 2020 a team of astronomers announced that they could have found evidence of the phosphine molecule in the atmosphere of Venus. Normally, this would be a rather esoteric discovery, but what happens is that I would not expect to find this particular molecule in it, as it is quite easily destroyed in the infernal environment of Venus … and, on Earth, phosphine. it is mainly produced by anaerobic bacteria. while they dine on dead things that were once alive.
So yes, it’s a big deal. But then this was questioned, with other scientists saying the data used was not calibrated with the proper files, which could make it look like phosphine was seen when it is not there. There were other issues as well.
The original team responded and said detection persisted when using updated calibration files, although it was weaker. But then things got interesting.
The astronomers who made the original discovery looked at a spectrum, dividing Venus’s light into individual colors. Different molecules absorb light with different specific colors, which allows them to be identified. However, sometimes molecules absorb very similar, if not overlapping, colors, confusing the problem. A new paper has published this point and says that sulfur dioxide (SO2) has been confused with phosphine, as it absorbs light at the same wavelength as phosphine.
It’s an interesting argument. Sulfur dioxide is known to exist in the Venusian atmosphere and they argue (using models of the planet’s atmosphere) that the signature seen in the data could be explained by SO2 existing in a layer about 80 km above the surface of Venus. It was claimed that phosphine was seen about 50 km away, but the new document argues that phosphine would be destroyed quickly 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 these data were at the limit of what could be seen, so without further observation, the problem may not be solved. I hope we will also hear more from the original team soon.
Going from a planet 40 million miles away to an inflated star 640 (or possibly 530) light-years away, we’re talking about Betelgeuse.
The iconic star surprised everyone in late 2019 when its brightness fell like a stone, fading around 50%. It was easily noticeable to the eyes and was quite brazen the speed with which it darkened.
Betelgeuse is a well-known variable star, with a brightness that varies by a certain percentage in a couple of different cycles. But this deep fall was unprecedented and strange. Astronomers immediately began to come up with ideas to explain it. One of them was a giant star, which turned out to be unlikely. Another was that perhaps his temperature dropped. A third, and the one that seemed to me probably due to the support of different sources, is that it caused a huge 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 guess: they show that part of Betelgeuse’s upper atmosphere could have cooled quite a bit, explaining the fall of the light.
Stars emit light because it is hot. If they cool, they become weaker. However, Betelgeuse is a red supergiant, a huge bag of gas more massive and much larger than the Sun. The physics of its outer layers is very complex and not very well understood.
The upper parts of the star physically expand and contract over a period of months to years, making the star brighter and fainter, changing its color and temperature slightly. In the new work, the authors show that parts of Betelgeuse’s upper atmosphere may have cooled by several hundred degrees, which explains the darkening.
They examined the molecule titanium oxide (TiO), which is commonly seen in very cool stars. It absorbs light with very specific colors in a characteristic way and what they found is that the absorption by TiO changed when Betelgeuse was weaker, indicating that it was colder than previously thought. The exact temperature drop is difficult to determine, but at one point it shows a clear drop of 150 Kelvin (one degree Celsius = 1 Kelvin). They claim that if the temperature dropped 250 K, then no dust is needed to explain the darkening.
Complicating this is that high-resolution star images show that only the southern hemisphere faded, so it is likely (reasoned) that the temperature drop occurred there. If the temperature dropped in only part of the atmosphere, it would be difficult to figure out how much, because the northern hemisphere remained the same, confusing the measure. Therefore, a drop of 250 K is not necessarily irrational.
It makes me wonder if there is more than one cause behind the darkening, 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 come together to increase their effect. I’m speculating here, but I certainly wouldn’t rule it out.
Funny: Venus is the brightest planet in our sky and the closest to Earth, and Betelgeuse is one of the brightest stars in the sky and also relatively close as the stars go. Still, for both of them, mysteries abound.
There are many things we know and understand well about the cosmos in which we live, but there are also many things, even about our neighbors next door. And these back-and-forth arguments of scientists about data, 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 hope both mysteries are solved to everyone’s satisfaction, and then we move on to the next weird thing Venus and Betelgeuse will do. This is how the Universe works.