Astronomers just discovered a bizarre star unlike anything we’ve ever seen before, according to research published in the journal Science. The star, which astronomers have nicknamed “Dox,” has an outer layer that is 99.9% oxygen, making it the most oxygen-rich atmosphere ever discovered. (Earth’s atmosphere is only about 21% oxygen.)

Previously, astronomers didn’t think it was possible for anything like this to exist, and it’s challenging our understanding of stellar evolution. The discovery “was incredibly unexpected,” astronomer Kepler de Souza Oliveira told Popular Mechanics. “And because we had no idea anything like it could even exist, that made it all the more difficult to find.” Dox is what astronomers call a white dwarf. Many stars eventually evolve into white dwarfs, which are dense objects made of the remnants of a star’s helium and hydrogen core. READ MORE