Przybylski's Star
Partially explainedSummary
In 1961 the Polish-Australian astronomer Antoni Przybylski took a spectrum of an unremarkable-looking star in Centaurus, and found that it contained almost no iron.
Stars are full of iron. This one is not. What it has instead is an extraordinary concentration of rare earth elements, and, according to some line identifications, traces of elements that should not be able to exist in it at all: actinides with half-lives measured in years and centuries, in a star that is billions of years old.
Somebody, at some point, was going to say that an alien civilisation was dumping nuclear waste into it, and somebody did.
The natural explanations are less exciting and more interesting, and neither of them is settled.
What is documented
The star. HD 101065, roughly 370 light-years away. It is a rapidly oscillating Ap star: a class of chemically peculiar star with an extremely strong magnetic field.
The missing iron. The spectrum shows abundances of iron and nickel far below what any ordinary star of its type carries.
What is there instead. Enormous overabundances of rare earth elements: strontium, holmium, europium, gadolinium, dysprosium, neodymium, and others. The spectrum is dense with their lines, thousands of them, overlapping.
The actinides. This is the claim that made the star famous. Lines in the spectrum have been attributed to short-lived actinide elements: actinium, protactinium, and, more controversially, elements including plutonium, americium, curium, berkelium, californium and einsteinium.
Several of these have half-lives measured in years, decades or centuries. In a star that has existed for billions of years, they should long since have decayed to nothing. Their presence, if real, requires that they are being produced continuously, right now.
Leading explanations
Chemical stratification in a strongly magnetised atmosphere. Established for the class.
Ap stars are chemically peculiar for a well-understood reason. They have very strong magnetic fields and very calm atmospheres, with little convective mixing. Under those conditions, two processes compete: gravity pulls elements down, and radiation pressure pushes some of them up.
Which elements get pushed up depends on how efficiently they absorb the star's light. Some are levitated into the photosphere and become enormously overrepresented there. Others sink out of sight.
The result is a surface whose composition tells you nothing about the star's actual bulk composition. What you are seeing is a sorted layer.
That accounts for the rare earths and it accounts for the absence of iron, and it is not controversial.
The actinides. Contested, and this is where the case lives.
They may not be there. This is the possibility that everybody skips over, and it is the strongest one.
The spectrum of Przybylski's Star is one of the most crowded ever recorded. It contains thousands of blended lines from rare earth elements, many of them not well characterised in laboratory data. Identifying a single line uniquely, in that forest, and attributing it to californium rather than to some unlisted transition of a lanthanide, is extremely difficult.
A misidentification is not a failure of competence. It is what a spectrum like this does to people.
They may be decay products of something heavier. This is the interesting hypothesis, and it is a real one in the literature.
If the star contained a long-lived superheavy element, one of the hypothesised nuclides on the so-called island of stability, its decay chain would produce exactly this: a continuous, replenished supply of short-lived actinides.
That would make Przybylski's Star the only known evidence for the island of stability, which physicists have been trying to reach in accelerators for half a century. It is unconfirmed and it is not absurd.
Alien nuclear waste. Proposed, semi-seriously, as a technosignature worth listing. It is on the record, and it is not the leading explanation, and it never has been. It requires the disposal of radioactive waste into a star by a civilisation, which is a great deal of machinery to invoke for an observation that two natural mechanisms already reach.
What the popular version gets wrong
"A star contains plutonium, which is impossible." A star may contain lines that may be plutonium. The identification is contested, the spectrum is one of the hardest to read in astronomy, and the honest description is that the actinide claim is unconfirmed.
"Scientists think aliens are dumping waste in it." They do not. It was raised as a hypothesis in a survey of things that would be worth looking for, which is what a responsible survey does, and it has been reported ever since as though somebody had proposed it as an explanation.
"The star is inexplicable." The class of star is well understood, and the mechanism that produces its bizarre surface composition, radiative levitation in a magnetised atmosphere, is standard astrophysics. What is unresolved is a specific set of line identifications.
"It would be the discovery of the century." If the actinides are real and are decay products of a superheavy nuclide, it would be. That is a very large conditional resting on a very difficult spectrum.
Current status
Partially explained. The star's overall peculiarity is accounted for by well-established physics. The actinide identifications are contested, and the two live possibilities are that the lines have been misassigned, or that there is a superheavy element in that star which nobody on Earth has ever made.
The registry keeps this record because of the discipline it demands. The exciting reading requires the line identifications to be right. Almost nobody who repeats the exciting reading has looked at how hard the identifications are.
Sources
- Przybylski, A. (1961). Initial spectroscopic characterisation of HD 101065.
- Subsequent high-resolution spectroscopy of the star and analyses of its rare earth abundances.
- Published claims of actinide line identifications, including short-lived species, and the critical literature on the difficulty of line identification in the star's blended spectrum.
- Gopka, V. and colleagues, on the possibility that short-lived actinides are decay products of a long-lived superheavy nuclide.
- Standard literature on radiative diffusion and chemical stratification in magnetic Ap stars.
Last reviewed: July 2026. Records are provisional. Where the evidence changes, the entry changes. Found an error? Tell us.