The story of a black hole in Cygnus, the swan, is like the tale of an angler – there’s the star it caught, and the one that got away.

V404 Cygni is about 7800 light-years away. It appears fairly close to the star that marks the intersection of the swan’s body and wings, which is high in the sky at dawn.

The system was first noticed in 1938, when it flared up – a performance it’s repeated several times.

Later, it was discovered that V404 Cygni is a tight binary: a black hole about nine times the mass of the Sun, plus a “normal” star a little less massive than the Sun.

The black hole is pulling gas from the companion. The gas forms a disk around the black hole. Every couple of decades, so much gas piles up that it sets off an explosion. That makes the system shine thousands of times brighter.

Recently, astronomers found that what looked like a background star probably is bound to the other two. It’s more than 300 billion miles from them. It’s bigger and heavier than the Sun, and is puffing up to become a giant.

This third star is about four billion years old – suggesting that the black hole is also that old. The black hole is the corpse of a massive star. Most such stars explode, hurling away any companions. This star must have collapsed completely, without exploding. Since then, it’s consumed at least half of its close companion – but the distant one got away.

Script by Damond Benningfield