I have a few updates on some of the news I’ve been following for some time, both causing quite a stir when it was first announced: phosphine in the atmosphere of Venus and dust that caused the Betelgeuse to fade in late 2019 / early 2020.
You may 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 pretty esoteric discovery, but the thing is, you wouldn’t expect to find that molecule there, because it’s quite easily destroyed in the infernal environment of Venus … and, on Earth, phosphine is produced primarily by anaerobic bacteria. while eating dead things that were alive.
So yes, kind of a big deal. But this has been questioned, with other scientists saying the data used was not calibrated using the right files, which could make it appear that phosphine was seen when it is not actually there. There were other problems.
The initial team then responded, saying that the detection persisted when they used updated calibration files, although it was weaker. But then things got interesting.
The astronomers who made the original discovery looked at a spectrum, breaking the light from Venus into individual colors. Different molecules absorb light in different specific colors, allowing them to be identified. However, sometimes the molecules absorb very similar, if not overlapping colors, confusing the problem. A new paper has appeared in this regard, saying that sulfur dioxide (SO2) has been confused with phosphine because it absorbs light at the same wavelength as phosphine.
It’s an interesting argument. It is known that sulfur dioxide exists in the Venusian atmosphere and they claim (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. Phosphine was claimed to have been seen about 50 km up, but the new paper claims that phosphine was quickly destroyed there.
The argument is convincing and could be very correct. Phosphine may not be what was seen in the first place. The problem here is that these data were on the edge of what could be seen, so without further observation, the problem may not be solved. I hope we hear more about the original team about this soon.
Moving from a planet 40 million kilometers away, to an inflated star 640 (or possibly 530) light-years away, let’s talk about Betelgeuse.
The iconic star shocked everyone at the end of 2019, when its brightness dropped like a stone, decreasing by about 50%. It was easy to see and quite strange how quickly it had faded.
Betelgeuse is a known variable star, with its brightness varying by a few percent over several different cycles. But this deep dive was unprecedented and strange. Astronomers immediately began to come up with ideas to explain it. One of them was giant giant stars, which turned out not to be very likely. Another was that his temperature probably dropped. A third, and the one I felt most likely due to support from different sources, is that a huge cloud of dust broke out that blocked some of its light.
But a new paper has just been published that brings the temperature up again. Or down, I suppose: it shows that part of Betelgeuse’s upper atmosphere could have cooled quite a bit, explaining the dimming.
The stars emit light because they are hot. If they cool down, they become weaker. However, Betelgeuse is a red supergiant, a huge, more massive and more distant bag of gas, 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 dimmer, slightly changing color and temperature. In the new paper, the authors show that parts of Betelgeuse’s upper atmosphere may have cooled by several hundred degrees, explaining the decrease.
They looked at the molecule of titanium oxide (TiO), which is commonly seen in very cold stars. It absorbs light in 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 drop in temperature is difficult to determine, but at one point shows a clear drop of 150 Kelvin (one degree Celsius = 1 Kelvin). They claim that if the temperature drops by 250 K, then no dust is needed to explain the fading.
Complicating this is the fact that images with an extremely high resolution of the star show that only the southern hemisphere has faded, so it is likely (motivates) that the drop in temperature occurred there. If the temperature dropped in only part of the atmosphere, it would be difficult to know how much, because the northern hemisphere remained the same, confusing the measurement. So a 250K drop is not necessarily unreasonable.
It makes me wonder if more than one cause is behind the decrease, both dust and temperature drop. This is not excluded; when something extreme happens in the Universe, it is usually because two or more phenomena have grouped together to increase their effect. I’m speculating here, but I certainly wouldn’t rule this 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. However, for both, mysteries abound.
There are many things we know and understand well about the cosmos we live in, but there are also many things we do not know, even about our neighbors. And these back-and-forth arguments of scientists about data, cause, and physics are normal for science; when we exceed the limits of knowledge, it takes time to realize what we see. I expect both mysteries to be solved to everyone’s satisfaction, and then we’ll move on to the next weird thing Venus and Betelgeuse will do. This is how the Universe works.