Astronomer David Kipping, of Cool Worlds fame, has urged other astronomers to use their telescope time to observe a particularly unusual star that appears to have a very strange or “seemingly impossible” chemical abundances.
In recent years, we have observed some stars acting seriously strangely. The classic example is KIC 8462852, better known as Boyajian’s star, or just the “alien megastructure” star. In 2016 and 2017, the star dimmed in unusual ways, leading some to suggest it could have a “Dyson sphere” around it, created by some advanced alien civilization. It turned out to be dust obscuring our view of the star, which is of course disappointing to anyone hopeful of detecting advanced alien life.
But it is not the only star that has recently captured astronomers’ attention.
One – HD 101065, or “Przybylski’s Star” – has pretty much all other stars beat for its weirdness. Even if it isn’t aliens (and we should assume that it is not, until all other natural explanations are exhausted), it could be doing something almost as cool.
The star, though it has been largely ignored, has recently caught the attention of Jason Wright, professor in the Department of Astronomy and Astrophysics in the Eberly College of Science at Pennsylvania State University; and David Kipping, assistant professor of astronomy at Columbia University and originator of some pretty awesome ideas including the Halo Drive and turning the Earth into a telescope.
HD 101065 was first discovered in 1961 by Polish-Australian astronomer Antoni Przybylski, and was immediately noticed to be unusual. The star, thought to be a little hotter than our Sun, is known as an “Ap” star, meaning a type A star that is chemically peculiar.
A-type stars themselves are pretty strange. Unlike stars such as our Sun, hot A-type stars usually do not have a magnetic field to slow their incredible rotation speeds imparted on them as they were formed. As a result, they usually retain their incredible spin, making it difficult to analyze their spectra.
But Ap stars are different. They do have a strong magnetic field, and rotate slowly. This allows us to get a really good look at the chemical makeup of their atmospheres, Wright explains in a blog post on the topic.
When we do analyze the light from these stars, it shows that they contain abundances of silicon, chromium, strontium, europium, and other rare Earth elements in their upper atmosphere.
But Przybylski’s star is stranger still, and appears to contain elements it really shouldn’t, at least by any mechanism we have come across in nature.
“It is believed to be an extreme member of a class of stars whose surface chemical peculiarities are generally thought to be a consequence of chemical separation,” one team wrote of the star in 2004. “This theory alone, however, would not account for the presence of elements with no long-lived stable isotopes.”
For instance, it appears to contain promethium. This is really weird. No known isotope of promethium has a half-life longer than 17.7 years, meaning that it must be produced by some continuous process if we are to see it in Przybylski’s star. Further analysis showed it contains actinium, protactinium, neptunium, plutonium, americium, curium, berkelium, californium, and einsteinium. These are difficult to confirm because they do not occur in nature (except, it seems, in Przybylski’s star).
“Unfortunately, these spectra have been poorly studied,” one team, which found short-lived elements in the spectra, explained. “For example, the wavelengths of only 22 lines are known for the singly ionized californium, which has been relatively well studied. Virtually all tables of spectral lines contain no data on technetium, promethium, and elements with atomic numbers Z > 83, save for thorium and uranium.”
Einsteinium was first discovered in 1952 during the first detonation of a hydrogen bomb and is considered a synthetic element, or one that could only be created by humans, and we have not produced a lot of it – and yet it has been tentatively detected in the star. Californium is also considered a synthetic element and was only discovered as a product after bombarding curium-242 with helium ions. Meanwhile, iron – usually one of the clearest lines seen in the light from stars – is barely seen at all.
So what the hell are these elements, many with short half-lives on astronomical timescales, doing in abundance in the atmosphere of an already unusual type of star? Despite over 60 years of knowing about the star, and some big leaps in astronomy techniques, we still do not know what’s going on. There are a few ideas, some sensible but weirdly unlikely, and a few very exciting explanations indeed.
One possible explanation proposed was that the star has a neutron star companion, which bombards the upper atmosphere of Przybylski’s star, causing reactions that produce the elements we observe. But the star does not look like it has such a companion, which leaves us with a few other (far more exotic) explanations.
One, which is outlined in a 2017 arXiv paper, is that the unusual elements are the result of the decay of undiscovered heavy elements in the hypothetical “island of stability” predicted by physicists, where elements could be stable once more.
“Spectral lines belonging to the short-lifetime heavy radioactive elements up to Es (Z=99) have been found in the spectra of the Przybylski’s star,” the paper explains. “We suggest that these unstable elements may be decay products of a ‘magic’ metastable nucleus belonging to the […] island of stability where the nuclei have a magic number of neutrons N = 184.”
The team suggests that this could have been produced in a nearby supernova. If correct, and more study would of course be needed, that would be pretty awesome. But there is another suggestion – whispered about, according to Wright – that it could be the sign of intelligent life.
There have been suggestions in the past that alien species could dispose of waste on the surface of their stars, which could be an explanation, though that seems unlikely. But it has also been suggested by Carl Sagan and Iosif Shklovskii that advanced alien civilizations could purposely put unusual and clearly manufactured elements into their stars in order to attract attention.
Sending signals out into the cosmos is energy-expensive, and given the distances involved, you do not know whether your signal will reach a civilization you believe could be there based on your observations, or a civilization that died in the interim.
It might make more sense instead, for a civilization bored of being alone, to simply place unambiguous signs that any other civilizations who have done their science will know is a sign of tampering. Why spend energy contacting every possible star, when you can simply place a huge sign saying “We are here” or, at least, one saying “Take a closer look at this star, something interesting is going on”?
That’s pretty speculative of course, and there will very likely be a natural explanation, such as the island of stability – which, let’s face it, is also really awesome. Or it could be that astronomers are misinterpreting these lines, which would also be useful to know. Finding out will require more observations of the star. Though Kipping does get access to telescopes, observations will need to take place in the global south in order to actually see it.
“I don’t understand why that hasn’t happened and I hope that us talking about it and my video and your podcasts actually inspire an astronomer out there to spend an hour of their precious telescope time […] just seeing do you at least see the same spectral features,” Kipping told the Event Horizon podcast. “That’s the first question and then if you do see the same spectral features the next question is okay, we believe them, but what are those lines? Is there any alternative to these radioactive elements? Could it be something else?”
[H/T: Cool Worlds]
An earlier version of this article was published in July 2024.
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