> the nearest two are V616 Mon at 11 solar masses and 3000 LY away, and Cyg X1 at 15 SM and 6000 LY. The nearest known ones, that is. They were detected due to

> the nearest two are V616 Mon at 11 solar masses and 3000 LY away, and Cyg X1 at 15 SM and 6000 LY. The nearest known ones, that is. They were detected due to their gravitational effect on binary companions we could more easily detect. By that token, it is quite possible there are nearer ones - it's just that detecting them directly if they don't have a binary companion is tough.