Astronomer David Kipping, of Cool Worlds fame, has asked other astronomers to use their telescope time to observe a particularly unusual star that appears to have a very strange or “seemingly impossible” chemical abundance.
In recent years, we’ve observed some stars behaving seriously strangely. The classic example is KIC 8462852, better known as Boyajian’s star, or simply the “alien megastructure” star. In 2016 and 2017, the star dimmed in unusual ways, leading some to suggest that there might be a “Dyson sphere” around it, created by an advanced alien civilization. It turned out to be dust obscuring our view of the star, which is certainly disappointing for anyone hoping to detect advanced alien life.
But it is not the only star that has recently attracted the attention of astronomers.
One — HD 101065, or “Przybylski’s Star” — has nearly all other stars beaten for its strangeness. Even if it’s not aliens (and we have to assume it’s not, until all other natural explanations are exhausted), it might 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 in the Eberly College of Science at Pennsylvania State University; and David Kipping, assistant professor of astronomy at Columbia University and creator 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 noted to be 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 special.
A-type stars themselves are quite strange. Unlike stars like our Sun, hot A-type stars don’t usually have a magnetic field to slow down their incredible rotation speed given to them when they formed. As a result, they usually retain their incredible spin, making it difficult to analyze their spectra.
But Ap’s stars are different. they I DO they have a strong magnetic field and spin slowly. This allows us to get a really good look at the chemistry of their atmosphere, Wright explains in a blog post on the subject.
When we analyze the light of these stars, it shows that they contain an abundance 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’ve encountered in nature.
“It is believed to be an extreme member of a class of stars whose surface chemical features are generally thought to result from chemical fission,” a team wrote about the star in 2004. “However, this theory alone would not account for the presence of elements without long-lived stable isotopes.”
For example, it appears to contain promethium. This is really strange. No known isotope of promethium has a half-life longer than 17.7 years, which means it must be produced by a continuous process if we want to see it 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 Przybylski’s star).
“Unfortunately, these spectra are poorly studied,” explained a team that found short-lived elements in the spectra. “For example, the wavelengths of only 22 lines are known for the single ionized californium, which has been relatively well studied. Almost all tables of spectral lines do not contain data for technetium, promethium, and elements with atomic numbers Z > 83 , with the exception of thorium and uranium”.
Einstein was first discovered in 1952 during the first hydrogen bomb explosion and is considered a synthetic element, or an element that could only be created by humans, and we haven’t made much of it – and yet it is previously discovered in the star. Californium is also considered a synthetic element and was discovered as a product only after bombarding curium-242 with helium ions. Meanwhile, iron – usually one of the clearest lines seen in starlight – is barely visible at all.
So what on earth are these elements, many with short half-lives on astronomical time scales, doing in abundance in the atmosphere of an already unusual type of star? Despite over 60 years of knowing about the star and some great strides in astronomical techniques, we still don’t know what’s going on. There are some ideas, some reasonable but surprisingly improbable, and some really exciting explanations.
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 doesn’t seem to have such a companion, which leaves us with some other (much more exotic) explanations.
One, described in a 2017 arXiv paper, is that the unusual elements are the result of the decay of undetected heavy elements on the hypothetical “island of stability” envisioned by physicists, where the elements could be stable even a times.
“Spectral lines belonging to short-lived radioactive heavy elements up to Es (Z=99) have been found in the spectra of Przybylski’s star,” the paper explains. “We suggest that these unstable elements may be the decay products of a metastable ‘magic’ core belonging to […] island of stability where nuclei have a magic number of neutrons N = 184.”
The team suggests that this could have been produced in a nearby supernova. If it is correct, and more study will certainly be needed, that would be pretty cool. But there’s another hint—whispered, according to Wright—that it could be the sign of intelligent life.
There have been suggestions in the past that alien species may dump debris on the surface of their stars, which could be an explanation, although it seems unlikely. But it has also been suggested by Carl Sagan and Iosif Shklovskii that advanced alien civilizations may deliberately place unusual and clearly manufactured elements in their stars in order to attract attention.
Sending signals into space is expensive in energy, and given the distances involved, you don’t know if your signal will reach a civilization you believe may be out there based on your observations, or a civilization that died in the time.
Rather, it might make more sense for a civilization bored of being alone to simply put up vague signs that any other civilization that has done their own science would know to be a sign of harassment. Why waste energy contacting every possible star when you can just put up a big sign that says “We’re here” or, at the very least, one that says “Take a closer look at this star, something interesting is happening”?
Of course, this is pretty speculative, and there’s most likely a natural explanation, such as the Island of Stability – which, let’s face it, is also really cool. Or it could be that astronomers are misinterpreting these lines, which would also be useful to know. Discovery will require more observations of the star. Although Kipping has access to telescopes, observations would have to occur in the global south to see it.
“I don’t understand why this hasn’t happened and I hope that us talking about it and my video and your podcasts will inspire an astronomer out there to spend an hour of their precious telescope time. […] just looking at do you see at least 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 OK, we believe them, but which are those lines? Are there any alternatives to these radioactive elements? Could it be something else?”
[H/T: Cool Worlds]
An earlier version of this article was published in July 2024.