Przybylski's Star

Przybylski’s star, or HD 101065 in the constellation of Centaurus, appears to be even more difficult to understand than to pronounce. (It is named after Polish-Australian astronomer Antoni Przybylski, who described it in 1961.)

From the star’s spectrum, it appears to contain very small amounts of iron and nickel, which normally would be abundant in a star of this type, but is wildly over-abundant in screwball elements such as strontium, holmium, niobium, scandium, yttrium, cæsium, neodymium, praseodymium, thorium, ytterbium, and uranium.

If that weren’t weird enough, the spectrum seems to indicate the presence of numerous short-lived actinide elements, including actinium, protactinium, neptunium, plutonium, americium, curium, berkelium, californium, and einsteinium, the latter of which has no known isotope with a half-life longer than 472 days.

What is going on? Basically, nobody has a clue. Astrophysics knows of no mechanism by which such a star could create such elements. The radioactive elements, if formed in a supernova from whose debris the star formed, would have decayed away billions of years ago. Could the anomalous elements be decay products from long-lived island of stability nuclei created in a supernova? Well, maybe, but why haven’t such products been seen in any other star. Theories that the elements were formed in a companion neutron star founder on the inability to find such a star.

I’m not saying it’s aliens, but in the 1966 book Intelligent Life in the Universe, Carl Sagan and I. S. Schklovskii speculated that an economical way for a technological civilisation to announce its presence would be to dump “impossible” elements into its star, creating an unnatural spectral signature which could be detected by any other civilisation that did a spectral survey of stars visible to it.


Very peculiar! We are looking at something which happened about 355 Million years ago, which raises the question of what it might look like right now? If the apparently-observed short-lived radioactive isotopes are indeed real, then we might be looking at a very short phase in a star’s life – which would explain the rarity of the observation.

On the other hand, what are the uncertainties around the observation? The data come from spectral analysis of the light from a single star – a type of analysis which is common, but which clearly requires a staggering level of technology. There is a website discussing the analyses of various spectra measured on this star:
Przybylski’s Most Unusual Star (

I have to admit I can barely understand a word of the website – except to note that analyzing a star’s spectrum is apparently a highly skilled task subject to assumptions (deductions?) about inputs such as the star’s temperature, along with a fair amount of interpretation. Maybe this star is not quite as unusual as it first seems?