Last time I promised three solutions to the problem of short-lived actinides in the atmosphere of Przybylski’s Star. Here they are:
1) Neutron Stars
In 2008, shortly after identifying the “impossible” elements in Przybylski’s Star, Gopka et al. proposed a solution: the star has a neutron star companion. Neutron stars have strong winds of positrons and electrons that bombard the heavy elements in the atmosphere of the star, transmuting them to the elements we see.
The big problem with this is that these are sharp lines, so we can measure radial velocities to Przybylski’s Star, and it does not have a short period neutron star companion. Which is great, because the last two solutions are even more fun.
2) Flerovium, Unbinilium, Unbihexium
A few days ago I saw this from William Keel on Twitter:
TIL via arxiv: Przybylski's star shows every element in its spectrum from neptunium to einsteinium (93-99). https://t.co/VAeUCgVpFD
— William Keel (@NGC3314) March 14, 2017
Following his link, I found a delightful proposal for Przybylski’s Star.
Atomic physicists have long sought to fill out the periodic table of the elements. Since the discovery of Francium in 1939, all additions to the periodic table have come from elements synthesized through nuclear reactions. Every few years you’ll see a news item about one of the teams around the world that has finally proven that they have produced a tiny, fleeting sample of some heavy element, by detecting its presence before it decays away in seconds (or less!).
There is reason to believe, though, that there might be longer-lived elements higher up the table, in an “island of stability” that experimenters have yet to reach. This is a region of the Table of the Isotopes that might have unusually stable members because they contain a “magic number” of neutrons and protons. According to Wikipedia:
Many physicists think [these isotopes’ half-lives] are relatively short, on the order of minutes or days.[2] Some theoretical calculations indicate that their half-lives may be long, on the order of 109 years.[14]
Enter Dzuba, Flambaum, and Webb, who propose that the source of the short-lived actinides in Przybylski’s Star is one of these isotopes! As the isotope decays, its daughter products—all less massive than it but still actinides—are visible in the star before they decay away. There would be some steady-state concentration dictated by the lifetime of the isotope. They propose the parent isotope could be 298Fl, 304Ubn, or 310Ubh.
If this is right then it means that we can discover a new, important isotope the old fashioned way—in nature! It would not be a first element to be found first in a star, though—helium is so named because it was first discovered in the Sun.
But where would it come from? Dzuba et al. suggest that it might be the product of a supernova explosion, like other neutron-heavy elements. Its half life could be short enough that it would be present in a young A star but very rare on the Earth—or perhaps you need a certain kind of supernova to make it, and one of those wasn’t in the mix that generated the elements that make the Earth. If so, it could be common in other stars and planets, but just very hard to detect in anything other than an Ap star with levitation.
Very cool!
3) Aliens
The last of the three solutions I’m aware of, whispered but never published, is that it’s the product of artificial nuclear fusion.
Here on Earth, people sometimes propose to dispose of our nuclear waste by throwing it into the Sun (in one case, literally throwing it:)
(This is a terrible idea, by the way. I mean putting nuclear material on top of giant towers filled with rocket fuel and igniting them—but Superman IV too.)
In fact, 7 years before Superman thought of the idea, Whitmire & Wright (not me, I was only 3 in 1980) proposed that alien civilizations might use their stars as depositories for their fissile waste (because of course alien civilizations would use 20th century nuclear technology for their energy needs…but I digress). They even pointed out that the most likely stars we would find such pollution in would be… A stars! (And not just any A stars, late A stars, which is what Przybylski’s Star is). In fact, back in 1966, Sagan and Shklovskii in their book Intelligent Life in the Universe proposed aliens might “salt” their stars with obviously artificial elements to attract attention.
So short lived, obviously artificial elements in A stars are in fact a prediction of artifact SETI!
This just goes to show that artifact SETI is hard. When people stick their necks out and make bold, silly-sounding predictions about unambiguous technosignatures like this (or like megastructures), I suspect they usually don’t actually expect them to come true. And then when they do come true (as in Przybylski’s Star, KIC 12557548, or Boyajian’s Star) not only are their prediction papers rarely cited (which is, I think, inappropriate), but there’s always immediately a flurry of perfectly natural explanations that arrive to explain things without aliens (which is, I think, totally appropriate).
I think the answer to SETI will ultimately come, if it comes at all, from communication SETI because the signals it seeks are pretty unambiguous, but who knows? If that narrow band microwave carrier wave is ever found and we can’t decode it, maybe some plausible natural maser emission source will be hypothesized to explain it away, too?
We should keep trying though, because even when artifact SETI finds no aliens, it finds interesting things. After all, regardless of what the solution to Przybylski’s Star is, it’s bound to be fascinating!
Anyway, that’s the end of this series. I know that Tabby’s Star is supposed to be The Most Mysterious Star in Our Galaxy, but I think Przybylski’s Star gives it a run for its money.
Edit: One more part: a caveat I had meant to include earlier but inadvertently edited out.
I find Pryzybylski’s Star fascinating, and while enjoying this post series about it I did a double-take at that Dzuba, Flambaum, and Webb paper, because Dzuba and Flambaum are co-authors on the papers that came out of my PhD, and Webb was my supervisor’s supervisor. I started my PhD about 6 months after that paper came out, and never knew about it before.
(We collaborated with Dzuba and Flambaum for my work on searching for variation in the fine-structure constant by constraining changes in the frequencies of atomic transitions in stellar spectra – they did the theoretical work for what magnitude of variation might be possible in transition frequencies if the fine-structure constant were to change.)
If it has a neutron star companion, and the plane of the orbit happens to be perpendicular to the line of sight, you still get sharp spectral lines, right?
Jason, an older Thorne-Zytkow object where the wobble has all but disappeared and that’s a little warmer and less luminous than theory predicts seems like a good explanation. Why does it seem like that’s too hard of a pill to swallow.
Also possible: The reason why they are dumping nuclear waste this way is likely because they have a lot of it. As in entire planets covered in gigantic hybrid reactors using neutrons from DT fusion to induce fission in thorium similar to an accelerator-driven reactor and make other useful isotopes such as 238Pu and 180Ta.
Did I mention that said planets are probably uninhabited?
Its not as ridiculous as it sounds, if you scale up a fusion reactor enough even with heroic measures the core becomes unstable. So making lots of them is a good way to generate a vast amount of power eg for mass producing antimatter.
Ap stars like Przybylski’s star are still fusing hydrogen in their cores, and their cores are nowhere near the conditions in which neutron stars or supernovae would form. Also, the elemental abundances of the surfaces of these stars are almost completely disconnected from the nuclear processes in the core—the only mechanism that could connect the two would be diffusion through the radiative regions which is extremely slow, and operates on timescales much longer than the age of a star like this.
This makes me try to apply different elements of other stars’ structures to Przybyliski’s Star. What if this star was *just* under the solar limit for the formation for neutron stars during a supernova? I imagine that the quarks weren’t rearranged into neutrons, but instead the subatomic particles instead shifted all the way up into the conditions necessary for the island of stability. Maybe, during a rare supernova-like event that we haven’t spotted, the entire elemental composition of the star compressed into these elements through a one time fusion at this strange solar mass sweet spot? Might the missing stars of solar masses that create neutron stars that we’ve seen actually BE Ap stars like this one?
Przybylski’s Star is a favorite star of mine as well to think about, and its heavy element composition turns everything I know about stellar fusion sideways, opening a ton of wild theories to run with. I wish I could help solve the mystery!
Yes, that’s called a Thorne Żytkow object when the NS makes it to the core—those are very large red giant stars. I don’t know the timescale for the NS to make it into the center of the star, but this star has no big center-of-mass motions, so it can’t be one of those.
https://en.wikipedia.org/wiki/Thorne%E2%80%93%C5%BBytkow_object
Is it possible for a neutron star to be orbiting inside a large A star? How long could it orbit before drag caused it to sink to the stellar core?
Crazy theory: What if Przybylski’s star was an unimploded netron star, with enough mass ejected for electron degeneracy pressure to kick in again, large clusters of neutrons trying to form electron-proton atoms again. The star reignights, a single kilometer wide atomic nucleus starts a rapid chain reaction of nuclear fission, lots of unstable elements rapidly decay, with the observed residual chemistry matching the nuclear islands of stability.
No, Thorne-Żytow objects should be much colder and more luminous than Przybylski’s Star.
I was wondering if Przybylski’s Star might be a kind of Thorne–Żytkow object. Instead of having a typical neutron star, maybe it’s either got one big enough to be on the verge of becoming a black hole, or already a black hole.
Matter might approach a gravitational gradient where it gets fused to these heavier elements, but not close enough to be ingested.
Type 1a civilization maybe? They might not even consider that other civilizations could sense the spectra.
370 years is a long time to wait.
I always find it ironic that the same people who lament the supposed Fermi paradox are also the ones who immediately dismiss out of hand any hypothesis for unusual phenomena that might involve aliens.
More likely it was never submitted, I was speculating.
Whether a “maybe it’s aliens” paper gets published depends a lot on the particular referee, and even so it probably needs a lot more than just that.
I really don’t understand what’s up with these astrophysicists, they must be a terribly stuffy lot if your explanation 3 never got past a journal referee. There were oodles of publications about cold fusion, and loads about the more recent sunoffusion as well. In fact some very distinguished names appear on the author lists of sunoffusion papers. So if that nonsense could get published, why not explanation 3?
First, A stars fun out of fuel before complex life can start to form on their habitable planets. But, this argument CAN be circumvented if one of its planets were COLONIZED. Next, ET’s would have to be dumping ^#@&%##loads of nuclear waste onto the star for a ground based telescope on Earth to detect their spectra.