Astronomer David Kipping, known for his work on Cool Worlds, 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 abundance.
In recent years, we have observed stars behaving in very strange ways. The classic example is KIC 8462852, better known as Boyajian’s Star, or simply an “alien megastructure” star. In 2016 and 2017, the star dimmed in an unusual way, leading some to suggest that it might be surrounded by a “Dyson sphere,” created by an advanced alien civilization. This turned out to be dust obscuring our view of the star, which is of course disappointing for anyone hoping to detect advanced alien life.
But it’s not the only star that has recently caught the attention of astronomers.
One of them, HD 101065, or “Przybylski’s Star,” surpasses almost all other stars in terms of weirdness. Even if it’s not an alien star (and we should assume it isn’t, until all other natural explanations are exhausted), it could be doing something almost as cool.
The star, though largely overlooked, has 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, an assistant professor of astronomy at Columbia University and the brainchild of some pretty impressive ideas, including the Halo Drive and turning Earth into a telescope.
HD 101065 was first discovered in 1961 by Polish-Australian astronomer Antoni Przybylski, and was immediately noted for its unusual nature. The star, thought to be slightly hotter than our Sun, is known as an “Ap” star, meaning chemically unusual A-type.
A-type stars are pretty strange themselves. Unlike stars like our Sun, hot A-type stars typically don’t have a magnetic field to slow down the incredible rotation speeds they were given when they formed. As a result, they typically retain their incredible rotation, making it difficult to analyze their spectra.
But the stars of Ap are different. They TO DO Asteroids have a strong magnetic field and rotate slowly. This gives us a very good insight into the chemical composition of their atmosphere, Wright explains in a blog post on the subject.
When we analyze the light from these stars, we find that they contain abundances of silicon, chromium, strontium, europium and other rare earth elements in their upper atmospheres.
But Przybylski’s Star is even stranger and seems to contain elements that it should not contain, at least according to the mechanisms we have encountered in nature.
“It is thought to be an extreme member of a class of stars whose surface chemical features are generally considered to be a consequence of chemical separation,” one team wrote of the star in 2004. “This theory alone, however, cannot explain the presence of elements without long-lived stable isotopes.”
For example, it appears to contain promethium. This is really weird. 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 are to see it in Przybylski’s Star. Further analysis has shown that it contains actinium, protactinium, neptunium, plutonium, americium, curium, berkelium, californium, and einsteinium. These elements are difficult to confirm because they do not exist in nature (except, apparently, in Przybylski’s Star).
“Unfortunately, these spectra have been poorly studied,” says a team that has discovered short-lived elements in these spectra. “For example, only the wavelengths of 22 lines are known for monoionized californium, which has been relatively well studied. Virtually all spectral line tables contain no data for technetium, promethium, and elements with atomic numbers Z > 83, with the exception of thorium and uranium.”
Einsteinium was first discovered in 1952 in the first hydrogen bomb explosion. It is considered a synthetic element, meaning one that could only be created by humans. We haven’t produced much 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. In contrast, iron – usually one of the sharpest lines seen in starlight – is barely visible.
So what are these elements, many of which have 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 this star and some considerable advances in astronomical techniques, we still don’t know what’s going on. There are a few ideas, some sensible but strangely unlikely, and some very interesting explanations.
One possible explanation has been put forward: the star has a neutron star companion that bombards the upper atmosphere of Przybylski’s star, causing reactions that produce the elements we observe. But the star does not appear to have such a companion, leaving us with a few other (much more exotic) explanations.
One, described 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 the elements could become stable again.
“Spectral lines belonging to short-lived heavy radioactive 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 could 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 phenomenon could have been produced by a nearby supernova. If so, and further study would of course be needed, it would be quite impressive. But there is another hypothesis – one that is being whispered, according to Wright – that it could be a sign of intelligent life.
It has been suggested in the past that alien species might dump their waste on the surface of their stars, which could be one explanation, although it seems unlikely. But Carl Sagan and Iosif Shklovskii have also suggested that advanced alien civilizations might deliberately place unusual and obviously manufactured items in their stars in order to attract attention.
Sending signals into the cosmos is energy-intensive, and given the distances involved, you don’t know whether your signal will reach a civilization you believe to be present based on your observations, or one that has died in the meantime.
Perhaps it would be wiser for a civilization tired of being alone to simply put up unambiguous signs that all other civilizations that have done their research will know are signs of an alteration. Why waste energy contacting every possible star, when you can just put up a huge sign that says “We’re here” or at least “Look closer at this star, something interesting is happening”?
This is of course quite speculative, and there will most likely be a natural explanation, like the island of stability – which, let’s face it, is also really impressive. It could also be that astronomers are misinterpreting these lines, which would also be useful to know. To find out, more observations of the star will be needed. Although Kipping has access to telescopes, observations will have to take place in the southern hemisphere to actually see it.
“I don’t understand why this hasn’t happened and I hope that the fact that we’re talking about this, that my video and your podcasts will actually inspire an astronomer to spend an hour of their precious telescope time … just to see if 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 okay, we believe them, but what are these lines? Is there an 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.