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The Challenges of Przybylski’s Star

About 370 light years away in the constellation Centaurus is a variable star whose spectrum continues to raise eyebrows. The star is laced with oddball elements like europium, gadolinium, terbium and holmium. Moreover, while iron and nickel appear in unusually low abundances, we get short-lived ultra-heavy elements, actinides like actinium, plutonium, americium and einsteinium. Hence the mystery: How can such short-lived elements persist in the atmosphere of a star? Discovered in 1961 by the Polish-American astronomer Antoni Przybylski, these traits have firmly placed Przybylski’s Star in the Ap class of chemically peculiar stars. Its very name is a cause of continuing conversation.

Well, true enough. If Przybylski’s Star is a challenge to understand, it’s also a challenge to pronounce. Charles Cowley (University of Michigan), who offers a detailed analysis of the star online, met Przybylski in 1964, asking him how to say his name. “He obliged me,” Cowley writes, “and I thought I detected a slight “puff” at the beginning of the sound, which Mike Bessel writes is like “jebilskee”, with the “je” as if it were in French. The initial “P” gets minimal sound.” I think we can go with that, although I’ve seen a variety of pronunciations online.

What we’d like to know once we can say the star’s name is how the heavy elements observed here have come about. A neutron star is one solution, a companion object whose outflow of particles could create heavy elements in Przybylski’s Star, and keep them replenished. The solution seems to work theoretically, but no neutron star is found anywhere near the star. In a new paper, Vladimir Dzuba (University of New South Wales) and colleagues suggest that the actinides in Przybylski’s Star are evidence of the slow decay of superheavy elements.

The idea is that there may be a so-called island of stability involving elements with 114 or more protons in their nuclei, super-heavy elements that nonetheless are long-lived. If these exist, then the short-lived plutonium, einsteinium and the rest found in the star would simply be decay products. We may be, in other words, about to discover a new isotope not produced as a fleeting sample in an experiment but as an element observed in nature. That in itself is not unusual: Penn State’s Jason Wright reminds us that helium was first found in the Sun.


Wright has written a four-part discussion of Przybylski’s Star that begins with Przybylski’s Star I: What’s that? and continues through internal links. As with everything Wright does, it’s informative and also hugely entertaining. Moreover, it takes us however briefly into SETI terrain as Wright raises the point that advanced civilizations might use stars to store nuclear waste, a notion broached by Daniel Whitmire and David Wright as far back as 1980, and considered as well by Carl Sagan and Iosif Shklovskii in their Intelligent Life in the Universe (Holden-Day, 1966). Whitmire and Wright even opined that the most likely stars in which we would find such pollution were late A stars like Przybylski’s Star.

Image: Antoni Przybylski in the early 1960’s. Credit: Mike Bessell (via Charles Cowley’s site).

So we can note that this unusual star could fit into the artifact SETI category even as we continue to figure out the natural reasons why it should show the spectrum that it does. Wright adds this interesting note about the entire field of so-called Dysonian SETI, which scours our astronomical data for anomalies that could be the signs of the workings of an advanced civilization. As we continue to see in the controversy over Boyajian’s Star, this area of study can be frustrating, especially when one is in the business of working out what we might find:

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).

We keep looking nonetheless because no matter what their origin, stars like Przybylski’s Star are fascinating in their own right. Meanwhile, Dzuba and team hope to pursue the island of stability elements and the idea that the actinides in Przybylski’s Star are the result of their slow and replenishing decay:

We hope that this work provides a motivation for a further progress in the measurements of the transition frequencies for superheavy elements, calculations of the isotope shifts and search for the corresponding transitions in astrophysical spectra.

Dzuba believes the next step should be a search for five elements with atomic numbers of 102 or more: nobelium (102), lawrencium (103), nihonium (113) and flerovium (114), as recounted in this New Scientist report on their work. The challenge is daunting, because while such elements could be part of the radioactive decay chain of stable super-heavy elements on the ‘island of stability,’ their half-lives are so short that their spectra are not well defined.

The original paper on Przybylski’s Star is Przybylski, “HD 101065-a G0 Star with High Metal Content,” Nature Vol. 189, Issue 4766 (1961), pp. 739 ff. (abstract). Amusingly enough, the paper was hidden in plain sight on the Internet for some time, invisible to ADS searches because the author’s name had been misspelled. That has now been fixed. The Dzuba paper is “Isotope shift and search for metastable superheavy elements in astrophysical data,” (preprint).


Comments on this entry are closed.

  • Norm Davison March 28, 2017, 12:34

    It strikes me that IF a significant fraction of the normal heavy elements are due to neutron star collisions, then you might expect to find a lot of very neutron-rich elements, even very heavy ones, in the debris. One of the main problems with producing elements in the possible island of stability in the laboratory is getting enough neutrons into them, but this should be “no problem” if you start from nearly pure neutrons.

    I’m not sure how you arrange to get an A star (or maybe a G or F) near a pair of colliding nuetron stars, and have it survive. But if it did survive, it might get seeded with a lot of stuff including super-heavy elements. It might even end up with a large recoil velocity.

    I’m trying to imagine seeing this scenario, but I think I would like to be a LONG distance way.

  • André Esteves March 28, 2017, 12:51

    If it’s sign of a past or present interplanetary nuclear war it could help definitely in fixing the extent of a civilization’s lifetime in the Drake equation… :)

  • Harry R Ray March 28, 2017, 13:37

    Where to start on THIS one?! First, the “p” in Ap stands for “peculiar”, but the “A” does not necessarily mean spectral type “A”. The overwhelming majority of them ARE A stars, but Wikipedia lists Przybylski’s Star as an F3H0 star(whatever THAT means). Next, a bit of irony: Antoni Przybylski-AP, AND F3 JUST HAPPENS TO BE THE SPECTRAL TYPE OF BOYAJIAN’S STAR! Now, let’s get serious. Unlike Boyajian’s Star tith its umpity zillion plausible explanations, Przybylski’s star has only the three mentioned in this post, plus a FOURTH NOT mentioned, that the observations were FLAWED, and the Actinides are actually NOT THERE! Keep in mind that the observations were made in 1961, and, to my knowledge, were never followed up to verify the authenticity(correct me if I am wrong, and I HOPE I am wrong). There should be MULTIPLE FOLLOW-UPS with SEVERAL of the MOST POWERFUL TELESCOPES on and off Earth just to be sure. The reason for this is simple: With the neutron star solution being rendered null and void by the lack of a neutron star, the REMAINING solutions are in the “Sagan Rule” category! Add that to the fact that Przybylski’s Star is JUST AS UNIQUE as Boyajian’s Star, and; IF the 1961 data are PROVEN to be correct, FAR MORE MYSTERIOUS!!! Of the two remaining solutions mentioned in this post, the “Island Of Stability” one is by far the most plausible one, because the AGE of Przybylski’s Star being only 56.6(plus or minus 27.9)million years(making the MAXIMUM age only 84.5 million years) it seams impossible that an advanced civilization ORIGINATED around it, and because of its youth, COLONIZATION is a bit of a stretch, too.

    • Alexander Tolley March 28, 2017, 14:47

      Keep in mind that the observations were made in 1961, and, to my knowledge, were never followed up to verify the authenticity

      It isn’t clear from the Dzuba paper is follow-ups have been done., and certainly none are mentioned in the Wikipedia page for the star.

      The paper states:

      For example, optical lines of many actinide atoms and ions up to einsteinium (Es, Z = 99) have been found in the spectra of the Przybylski’s
      star [6].

      The cited paper is:
      [6] V. F. Gopka, A. V. Yushchenko, V. A. Yushchenko, I. V.
      Ivanov, and C. Kim, Kinematics and Physics of Celestial
      Bodies 24, 89 (2008).

      However, it isn’t clear that this is correct.

      Dzuba then goes on:

      There are many high-quality atomic spectra calculations
      for superheavy elements (see, e.g. [11–18]). However,
      the accuracy of the calculations is not sufficiently
      high to reliably identify spectral lines in astrophysical
      [emphasis is mine- AT].

      I interpret this to mean there is some doubt about the spectral identification of super-heavy elements that are being posited as a possible source of the actinides in the 1961 paper. I would also want a confirmation of the original data. Misidentification errors have been made in the past, so confirmation is needed in case this becomes a snipe hunt.

      The bottom line for me is that this is far too premature to assume that this star has an excess of very heavy, let alone hypothesize stable, super-heavy elements.

      BTW, wasn’t the acquisition of the super-heavy element (Illyrion) part of the plot of Delaney’s “Nova”?

      • Harry R Ray March 29, 2017, 13:14

        Obviously there WERE follow-up observations, but none SPECIFICALLY TARGETING the star’s OPTICAL SPECTRUM! Case in point: Observations made by Swift, Chandra, or XMM Newton to look for a neutron star(or RV searches to look for a massive companion), and SURVEYS taking the star’s spectra at lower magnification than Przybylski’s observations, like SDSS. I always thought it would be prudent for Borra and Trottier to “data mine” the SDSS data on Boyajian’s Star and run the SAME FOURIER TRANSFORM ANALYSIS that lead to their discovery their odd 234 stars. I now think they should ADD Przybylski’s Star as well. If BOTH OF THESE STARS show the same pulses as the 234 they have in hand, I think it would make the WHOLE ASTRONOMICAL COMMUNITY stand up and notice!

    • andy March 29, 2017, 13:04

      The “Ho” in the spectral type is the chemical symbol for holmium, one of the lanthanide elements that is detected in the spectrum of Przybylski’s star. Given the unusual spectrum it’s not surprising that the classifications seem to be all over the place, from a quick search of SIMBAD/VizieR I’ve seen it assigned spectral types as early as B5 and as late as G0.

  • Jason Wright March 28, 2017, 15:13


    The spectral type of Przybylski’s Star is actually very unclear because it is so peculiar—it breaks the scale. It belongs to the same class (in the general sense of the term) as Ap stars, so I lumped it in with them for that reason.

    The identification of the actinides could certainly be erroneous—and until the Dzuba paper that was the community consensus because short-lived actinides (and prometheum) in a star seems *impossible*.

    But you are wrong that these identifications are from the 60’s, they are from the last 10 years. Przybylski only noted lanthanides in his work. The actinides have been identified by three different authors, as I describe in the edits to my blog post here:

    Crowley even writes: “The spectroscopic evidence is strong enough that we would declare promethium to be present without hesitation, if any of its isotopes were stable.”

    So Dzuba’s work is important because it provides a physical mechanism that makes the prior probability of actinides in the spectrum finite (not infinitesimal or zero), meaning that, for the first time, the actinide measurements could be right!

    Neutron stars are actually totally ruled out by the stable RVs and lack of UV/Xrays of this star, so we can ignore that one.

    • Harry R Ray March 29, 2017, 10:14

      I was aware that the identifications were recent. Perhaps this is just “splitting hairs”, but by concern is that the identifications came from DATA as a RESULT of Przybylski’s 1961 OBSERVATIONS! I am also well aware that spectroscopy was VERY GOOD back in 1961, but it is SO MUCH MORE ADVANCED NOW! The chances are that follow up spectroscopy will reveal the exact same spectral patterns NOW than back in 1961, but this is such a weird star that we need to be ABSOLUTELY SURE!

  • Michael March 28, 2017, 16:40

    You also get lead and barium stars, the star might just be in a short phase in its life span where it is churning up material from the interior.

  • J. Jason Wentworth March 28, 2017, 20:34

    While I wouldn’t bet a large sum on it, there is also the possibility that this is an example of a suggestion that Arthur C. Clarke made in “The Promise of Space”:

    An advanced civilization might “label” its star by dumping into its atmosphere large quantities of artificial elements that do not occur in nature, so that its spectrum would attract the attention of astronomers in other solar systems. Short-lived, unstable elements, whose abundance persisted in a star’s spectrum, would tend to attract even more curious attention. Also:

    This would be useful to METI (Messaging Extra-Terrestrial Intelligence)-minded exoplanetary inhabitants even if such a state of affairs in a star can be created and maintained via natural causes, because it is unusual and uncommon. Even exoplanetary astronomers who suspected that the star’s unusual characteristics were purely natural in origin would be observing the star, which would make them more likely to “see” a radio or laser message sent from the star’s planetary system. In addition:

    In some cases, Clarke wrote, the necessary quantities of such elements would be a few hundred thousand tons, which is not unreasonable. Electromagnetic launchers–perhaps used in concert with appropriately-timed, inner-planet (and/or outer-planet) gravity assists in order to further brake the “ingot-projectiles” so that they would fall into the star–could continuously project small amounts of the elements so that they would persist in the star’s spectrum.

    • Harry R Ray March 29, 2017, 10:27

      I do not believe that “an advanced civilization might “label” its star by dumping into its atmosphere large quantities of artificial elements…’ due to security concerns. However, ETI might “label” A star this way to announce PRESENCE but NOT location! Because, according to Jason Wright, the star’s spectrum “breaks the scale”, everything is under question, EVEN ITS AGE! It could even be an ARTIFICIALLY CREATED STAR made for some unknown reason by a KIII civilization!

  • Geoffrey Hillend March 28, 2017, 20:37

    Maybe Ap stars like Przybylski’s Star are like AGB stars in the way they make their rare heavy elements through the “S process” or slow neutron capture. Consequently no neutron star or binary system is needed. Maybe these elements are dredged up from the star core through the S process or slow neutron process so that the Ap star is undergoing some kind of convection process due to it moving off the main sequence hydrogen burning and a mass loss during healing burning. https://www.aavso.org/vsots_fgsge2

  • ljk March 29, 2017, 15:22

    Are we alone?

    The universe seems to be bursting with planets, and this is profoundly important — but not in the way we might expect.

    Caleb Scharf


    • Harry R Ray March 30, 2017, 9:40

      ljk, check this one out: International Journal of Astrobiology(currently listed on the exoplanet.eu website in the bibliography section): New numerical determination of habitability in the galaxy: the SETI connection. By Rodrigo Ramirez, Marco Gomez-Munoz, Roberto Vasquez, Patricia Nunez. In the ABSTRACT the authors stated that ROUGHLY ONE-HALF of Earth-like planets in the HZ are inhabited by primitive life(which I ASSUME means everything from Archea to Tardigrades), but, what ABSOLUTELY BLEW ME AWAY, is that they ALSO stated that 4%(!!!) of Earth-like planets in the HZ host TECHNOLOGICAL life. Unfortunately, there is NO PDF, so I could not access the FULL PAPER(I hope YOU have better luck)so what is lacking HERE is just what they mean by “Earth-like(i.e. JUST orbiting K-G-F stars, or do they include M stars, too). The RATIO of roughly 8% of planets with ANY life ALSO being not only INTELLEGENT but TECHNOLOGICAL AS WELL is FAR HIGHER than ANY ratio I have EVER SEEN BEFORE!

  • Geoffrey Hillend March 29, 2017, 16:20

    The S process is too slow to make Plutonium and other radioactive elements: https://en.wikipedia.org/wiki/S-process The neutron flux is higher and much faster in a supernova explosion. I doubt if there are radioactive elements really in Przybylski’s Star that they are the result of ET’s using the star as a nuclear waste dump which is too expensive to send to a star. Now we can recycle radioactive waste and burn it in a new kind of Fusion fission reactor which recycles the old waste and getting rid of the need to ever have to store it. https://news.utexas.edu/2009/01/27/nuclear_hybrid It’s logical to assume ET’s would follow our same technological evolution and come up with the same thing.

    • ljk March 29, 2017, 18:53

      Of course this does not preclude the possibility that an ETI might still dump nuclear material into their star to deliberately get the attention of other intelligences who might notice via spectroscopy that their sun contains elements not naturally produced by their class of star.

      See also:

      Whitmire, D. P., and Wright, D. P., Nuclear Waste Spectrum as
      Evidence of Technological Extraterrestrial Civilizations, Icarus,
      vol. 42, pp. 149-156, 1980

      From here:


      I refer especially to the section titled OPTICAL (VISIBLE) RADIATION.

  • Bruce Mayfield March 30, 2017, 11:01

    Any explanation for this star’s weird elemental abundances must account not only for the super heavies but also for the low iron content. The low Fe suggests that the heavy element’s source is not the star itself, so ETI dumping/seeding is raised, but might this unique star be getting “seeded” from an infall of natural super heavy element dust and or meteors?

    I realize that this idea just moves the source without explaining how the parent isotopes came to be. However, all possible natural explanations would need to be considered and eliminated before ETI ideas would be taken seriously.

    New elements not on our table are sprinkled through SF, very cool if they’re sprinkled through the odd star as well. Is this star the ONLY one with this element pattern?

  • Jim Franklin March 30, 2017, 11:55

    When considering the age and the other details of HD101065 it is worth referring to the paper published in 2008 by David Mkrtichian1, Artie Hatzes
    , and Hideyuki Saio (Asteroseismology of Przybylski’s Star with HARPS) which can be found here (http://iopscience.iop.org/article/10.1088/1742-6596/118/1/012017/pdf)

    “We detected a rich acoustic p-mode spectrum in HD101065 and found an accurate value for the general spacing between consecutive overtones of modes, ∆ν= 64.07 µHz. For the first time for a roAp star we find a “small” spacing of modes that we interpret as the excitation of the complete spectrum of l = 0-2 modes. The asteroseismic tuning of the frequencies of the theoretical models to observed ones yielded the best fit model of an age = 1.6E9yr, mass M =1.50 M⊙, luminosity, logL/L⊙=0.771, and magnetic field strength, Bp = 9.00 kG. This is one of the first asteroseismic determination of stellar model and magnetic field in a roAp star.”

    This seems to be the most accurate determination for the mass, age and overall spectral type of the star. Discussions about ETI’s seeding the star either as a result of waste disposal or as a marker are far fetched. Any civilisation that was sufficiently advanced would have far better solutions to it’s nuclear waste issues (if it even has any) or for the attraction of other civilisations.

    Whilst we may all want to have evidence of ETI’s found, when it comes to messing about with stars I think it highly unlikely that any advanced civilisation would undertake such a risky venture.

    • Harry R Ray March 30, 2017, 13:49

      Also stated in the paper: “…more than half of spectral lines in the spectrum are not identified…”. How many “island of stability” elements are there? My guess is not as many as one-half of all the elements and compounds ALREADY IDENTIFIED! WHAT DOES THIS MEAN? Exotic Actinide COMPOUNDS? Elements MORE MASSIVE than the “island of stability” elements? YIKES!!!

      • Bruce Mayfield March 30, 2017, 19:21

        Aren’t there many unidentified lines in many star’s spectra, including the Sun’s?

  • Martin June 30, 2017, 2:15

    Peculiar stars are quite widespread so the peculiarity is a natural phenomenon, appearing to be be bounded regions of a star’s surface where rare elements are levitated to the surface and the common elements descending. The lanthanide Europium can be detected in this state on many stars.

    It’s clear that Przybylski’s star’s peculiarity is off the charts, showing every actinide in crazy abundances when the isotopes we can produce synthetically on Earth can have half-lives of microseconds. I believe, as said above, some process is creating stable isotopes of atoms we have not yet got to which are decaying to give us the crazy spectrum, and the key for nature to operate in this space appears to be huge numbers of available neutrons.

    Given that the star is a prediction of artifact SETI, I don’t see why we are not checking this out too.