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 very strange or “seemingly impossible” chemical abundances.
In recent years, we have observed some stars behaving in some seriously strange ways. A 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 an unusual way, leading to speculation that there might be a “Dyson ball” around it, created by some advanced extraterrestrial civilization. It turned out to be dust obscuring our view of the star, which is of course disappointing for anyone hoping to detect advanced extraterrestrial life.
But it is not the only star that has recently caught the attention of astronomers.
One — HD 101065, or “Przybylski’s Star” — has nearly all the other stars for its strangeness. Even if they aren’t aliens (and we should assume they aren’t until all other natural explanations have been exhausted), it could be doing something almost as cool.
The star, though largely ignored, recently caught the attention of Jason Wright, a professor in the Department of Astronomy and Astrophysics at Pennsylvania State University’s Eberly College of Science; and David Kipping, Assistant Professor of Astronomy at Columbia University and creator of some pretty amazing 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 immediately noticed that it was unusual. The star, which is thought to be slightly hotter than our Sun, is known as an “Ap” star, meaning an A-type star that is chemically peculiar.
A-type stars are strange enough in their own right. Unlike stars like our Sun, hot A-type stars typically do not have a magnetic field to slow down the incredible rate of rotation they acquired upon their formation. As a result, they usually retain their incredible spin, making it difficult to analyze their spectra.
But Ap stars are different. They do they 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 analyze the light from these stars, it turns out that they contain an abundance of silicon, chromium, strontium, europium and other rare earth elements in their upper atmospheres.
But Przybylski’s star is even stranger, and appears to contain elements it shouldn’t really have, at least by any mechanism we’ve come across in nature.
“It is thought to be an extreme member of a class of stars whose surface chemical peculiarities are generally thought to be the result of chemical separation,” one team wrote about the star in 2004. “However, this theory alone would not explain the presence of elements without long-lived stable isotopes lifespan.”
For example, it appears to contain promethium. That’s really weird. No known isotope of promethium has a half-life longer than 17.7 years, meaning it must be produced by some continuous process if it is to be seen in Przybylski’s star. Further analysis showed that 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, apparently, in the Przybylski Star).
“Unfortunately, these spectra have been poorly studied,” explained one team that found short-lived elements in the spectra. “For example, for singly ionized californium, which has been relatively well studied, the wavelengths of only 22 lines are known. Virtually all spectral line tables contain no data for technetium, promethium, and elements with atomic numbers Z > 83, except for so-called thorium and uranium.”
Einsteinium was first discovered in 1952 in the first detonation of the hydrogen bomb and is considered a synthetic element or an element that only man could have made and we didn’t produce much of it – yet it was tentatively detected in a 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 brightest lines visible in starlight—is barely visible.
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 more than 60 years of knowledge about the star and several major leaps in astronomical techniques, we still don’t know what’s going on. There are several ideas, some reasonable but strangely implausible, and indeed some very exciting explanations.
One possible explanation was that the star has a companion neutron star that bombards the upper atmosphere of Przybylski’s star and causes reactions that produce the elements we observe. But the star does not appear to have such a companion, which offers us several other (far more exotic) explanations.
One, outlined in a 2017 arXiv paper, is that the unusual elements are the result of the decay of undiscovered heavy elements in a hypothetical “island of stability” predicted by physics, where the elements could become stable again.
“Spectral lines belonging to short-lived heavy radioactive elements up to Es (Z=99) were found in the spectra of the Przybylski star,” the article explains. “We suggest that these unstable elements may be the decay products of a ‘magical’ metastable core belonging to […] an island of stability where nuclei have the magic number of neutrons N = 184.”
The team suggests that it may have been produced in a nearby supernova. If this is correct, and of course more study would be needed, it would be pretty amazing. But there’s another suggestion — which Wright says has been whispered about — that it could be a sign of intelligent life.
There have been suggestions in the past that alien species may dispose of waste on the surface of their stars, which could be an explanation, although this seems unlikely. However, Carl Sagan and Iosif Shklovskii have also suggested that advanced extraterrestrial civilizations could deliberately insert unusual and clearly manufactured features into their stars to attract attention.
Sending signals into space is energy-intensive, and given the distances involved, you don’t know if your signal will reach a civilization that you think might be there based on your observations, or a civilization that has died in the meantime.
For a civilization bored with solitude, it might instead make more sense to simply put up clear signs that any other civilization that has done their science will know is a sign of manipulation. Why waste energy contacting every possible star when you can simply put up a huge “We’re here” sign or at least a “Look closer at this star, something interesting is happening” sign?
This is of course quite speculative and there will very likely be a natural explanation such as an island of stability – which, let’s face it, is also really awesome. Or it is possible that astronomers are misinterpreting these lines, which would also be useful to know. Finding out will require further observations of the star. Although Kipping has access to telescopes, the observation will have to take place in the global south to actually see it.
“I don’t understand why it hasn’t happened, and I hope that our talk about it and my video and your podcasts actually inspire astronomers to spend an hour of their precious time with the telescope. […] just when you see, you at least see the same spectral features,” Kipping told the Event Horizon podcast. “That’s the first question, and then if you see the same spectral features, the next question is fine, we believe them, but what are the lines? Is there an alternative to to these radioactive elements? Could it be something else?”
[H/T: Cool Worlds]
An earlier version of this article was published in July 2024.