Exoplanet astronomers urge others to aim telescopes at ‘seemingly impossible’ star HD 101065

Astronomer David Kipping, of Cool Worlds fame, has called on other astronomers to use their telescope time to observe a particularly unusual star that appears to have a very strange or “seemingly impossible” chemical composition.

In recent years, we have seen some stars behaving really 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 speculate that it might have a “Dyson sphere” around it, created by an advanced alien civilization. It turned out to be dust that was blocking our view of the star, which is of course disappointing for anyone hoping to discover advanced alien life.

But it’s not the only star to catch astronomers’ attention lately.

One – HD 101065, or “Przybylski’s Star” – pretty much beats all the other stars in the weirdness stakes. Even if it’s not aliens (and we have to assume it isn’t, until all other natural explanations have been exhausted), it could be doing something almost as cool.

Although the star has been largely ignored, it has 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, an assistant professor of astronomy at Columbia University and the creator of some great 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 as unusual. The star, thought to be slightly hotter than our Sun, is known as an “Ap” star, meaning it is a type A star that is chemically unusual.

A-type stars themselves are quite strange. Unlike stars like our own Sun, hot A-type stars typically lack a magnetic field to slow down the incredible rotation rates they acquired when they formed. As a result, they typically retain their incredible spin, making their spectra difficult to analyze.

But Ap stars are different. They Doing have a strong magnetic field and rotate slowly, allowing us to see the chemical composition of their atmospheres, Wright explains in a blog post on the subject.

When we analyze the light from these stars, we find that they contain large amounts of silicon, chromium, strontium, europium and other rare earth metals in their upper atmospheres.

But Przybylski’s star is even stranger, and appears to contain elements that shouldn’t actually be there, at least not according to the mechanisms we’ve encountered in nature so far.

“It is thought to be an extreme member of a class of stars whose surface chemistry is generally attributed to chemical segregation,” a team wrote of the star in 2004. “However, this theory alone would not explain 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, it seems, 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 singly ionized californium, which is relatively well studied. Virtually all tables of spectral lines do not contain data for technetium, promethium, and elements with atomic numbers Z > 83, except thorium and uranium.”

Einsteinium was first discovered in 1952 during the first detonation of a hydrogen bomb and is considered a synthetic element, or an element that can only be created by humans, and we have not 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. Meanwhile, iron – usually one of the brightest 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 the star and some major leaps 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 exciting explanations indeed.

One possible explanation that was 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 appear to have such a companion, which leaves us with a few other (much more exotic) explanations.

One of these, described in a 2017 arXiv paper, is that the unusual elements are the result of previously undiscovered heavy elements decaying into the hypothetical “island of stability” predicted by physicists, where elements could be stable again.

“Spectral lines belonging to the 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 could have been produced in a nearby supernova. If true, and of course more research would be needed, that would be pretty awesome. But there’s another suggestion – which Wright says is being whispered about – that it could be a sign of intelligent life.

There have been suggestions in the past that alien species could be dumping trash on the surface of their stars, which could be an explanation, although that seems unlikely. But Carl Sagan and Iosif Shklovskii have also suggested that advanced alien civilizations could be deliberately putting unusual and clearly manufactured elements into their stars to attract attention.

Sending signals out into space takes a lot of energy. Furthermore, given the distances involved, you don’t know whether your signal will reach a civilization that you think might exist there based on your observations, or a civilization that has died out in the meantime.

It might make more sense for a civilization that is tired of being alone to simply put up unambiguous signs that all other civilizations that have done their science know are signs of manipulation. Why go to the trouble of contacting every possible star when you can just put up a big sign that says “We are here” or, at the very least, a sign that says “Take a good look at this star, something interesting is going on”?

This is of course quite speculative and there is probably a natural explanation, such as the island of stability – which, let’s face it, is also really great. Or it could be that astronomers are misinterpreting these lines, which would also be useful to know. To find out, more observations of the star are needed. While Kipping will have access to telescopes, observations will have to be made in the global south to actually see it.

“I don’t understand why that hasn’t happened and I hope that talking about it and my video and your podcasts actually inspire an astronomer to spend an hour of their precious telescope time […] “Just see if you can at least see the same spectral signatures,” Kipping told the Event Horizon podcast. “That’s the first question, and then if you can see the same spectral signatures, 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.

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