The US military has released previously classified photos and films related to unidentified flying object (UFO) sightings, which mostly show something blurry moving strangely. Still, I hear that a friend of a friend has gone from thinking there's a 1% chance that UFOs are aliens to now believing it is 50%. Is he rational?

People are constantly seeing things in the sky they don't understand. The vast majority are airplanes, satellites, weather balloons, clouds, rocket launches, auroras, optical reflections and so on. But for some sightings, there's no known explanation. The problem is that people jump to the conclusion "unknown = aliens". And when you think about it, this is fairly odd. Why not angels?

Anyway, I like to do maths instead. The Bayes formula (below), a mainstay of statistics, gives the probability (Pr) of something, given some evidence.

Researchers at the University of Notre Dame have identified the first eclipsing magnetic propeller in a cataclysmic variable star system, according to research forthcoming in the Astrophysical Journal.

The star system, referred to as J0240, is only the second of its kind on record. It was identified in 2020 as an unusual cataclysmic variable—a binary system consisting of a white dwarf star and a mass-donating red star. Normally, the compact white dwarf star collects the donated gas and grows in mass. In J0240, however, the fast-spinning, magnetic white dwarf rejects the donor's gas and propels it out of the binary system.

"It takes a rapidly spinning dwarf with a strong magnetic field in order to create a propeller," said Peter Garnavich, professor of astrophysics and cosmology physics and chair of the Department of Physics at Notre Dame, and lead author of the study that presented evidence of the propeller system.