Fritz Leiber's short story "A Pail of Air" (available to read online at Project Gutenberg) is set in a post-apocalyptic world, with a family who believe they are the only survivors after the Earth left the Sun and its atmosphere froze solid. The cause of the apocalypse is said to have been a "dark star":
The dark star, as Pa went on telling it, rushed in pretty fast and there wasn't much time to get ready. At the beginning they tried to keep it a secret from most people, but then the truth came out, what with the earthquakes and floods—imagine, oceans of unfrozen water!—and people seeing stars blotted out by something on a clear night. [...] You see, the dark star was going through space faster than the Sun, and in the opposite direction, and it had to wrench the world considerably in order to take it away.
Is it possible to identify this "dark star" in terms of our knowledge of real-world astronomy? Was it a black hole? (It sounds implausible that a black hole would travel through space and snatch just a single planet away from its star, but how much was known about black holes in 1951 when this story was published?) Or is "dark star" just a sufficiently sci-fi and scary sounding term to suit the purposes of the story?