Przybylski's strange star

In 1961, astronomer Antoni Przybylski studied the spectrum of an unremarkable star in the constellation Centaurus and found something baffling. It had very little iron and an enormous abundance of heavy, rare elements, such as the lanthanides. Later studies even pointed to signs of short-lived radioactive elements, which should not last long there.

That strangeness opened the door to a bold idea. In 1980, a theoretical proposal suggested that a civilization might seed its star with radioactive material to announce its presence, and Przybylski's star became a frequent example in that discussion. Most astronomers, however, prefer natural explanations, such as magnetic fields that separate and concentrate elements on the surface, or the influence of a companion star. The detection of the radioactive elements is also disputed.