Last June 16 a mysterious very bright spot appeared in a small, otherwise not very remarkable galaxy 200 light years (60 megaparsecs) distant from us. In a matter of days it had become about 10 times brighter than the brightest of normal supernovas, which is extra weird because bright supernovas usually take a lot longer to reach a peak. For that and other reasons astronomers aren't entirely sure what it is. Possibilities include a newly formed black hole, a star being eaten by a black hole, or a bizarre sort of neutron star, though there are potential problems with all these explanations. On top of the other weirdness, the usual astronomical way of labeling supernovas resulted in this being designated AT2018cow, so of course everybody calls it "the cow." There's more at Wikipedia, the astronomical website EarthSky, the American Astronomical Society site AASNova, and a lot of other places (just search for AT2018cow).