In most cases, neutron stars and black holes seem to be accompanied by a brown or red dwarf if in a binary system. The rarest binary star arrangement I stumbled across once was a neutron star (or a black hole) with a main sequence F class star.
Has anyone ever found a multiple star with more than one stellar remnant? For example, binary white dwarf, BH+neutron star and so on? I cannot find any. Are systems such as these exceedingly rare or simply not generated?
Most of the time when two stellar remnants are in a binary with each other, usualy they have been around for millions of years, and therefore are really rare sometimes because they're probably some of the first stars in the galaxy, unless the galaxy is really old.