There is currently some debate about how common these very multiple systems are. It is pretty well known now that about 40-50% of systems are single stars, abo

There is currently some debate about how common these very multiple systems are. It is pretty well known now that about 40-50% of systems are single stars, about 40-45% of systems are binary systems, about 10% are triple systems, and around a few percent are quadruple systems. But it doesn't seem to be well known what fraction of systems are quintuple systems or larger, firstly because they are intrinsically rare, and secondly because the fifth star is usually very hard to find (it tends to be both faint and distant). It seems as though this fraction is probably around 1 percent, maybe a little less. A few years ago it was thought that the fraction of systems with different hierarchies followed a geometric series, but this doesn't seem to be borne out any more as the statistics have improved.