# Is every star formed in an open star cluster?

As far as I understand, an open cluster is formed from a single molecular cloud, with each star in the cluster having roughly similar age and properties.

Our Sun is not part of any star cluster, but it could have been formed in one. Is every star formed in an open star cluster, or can they develop independently?

• Hi, can you let us know if you know any of the theory about how stars form? Basically, why would you expect that star formation depends on the simultaneous formation of other stars several to hundreds of light-years distant? Sep 11 '19 at 14:58
• As far as I understand an open cluster is formed from the same molecular cloud, with each star in it having roughly similar age and properties. Sep 11 '19 at 15:29
• Yes normally a gas cluster should lead to several stars. The question should rather be if all stars are originally gravitationally bound to a cluster or not. The first seems the case, as for the original gas cluster is surely a collapsing one. The second night be possible as for the dynamics of the system could somehow eject the forming or new born star. Let us wait for an answer to this. Sep 12 '19 at 10:03
• Have you heard of Bok globules? They're smaller than GMCs (giant molecular clouds), and as Wikipedia says, they most commonly result in the formation of double- or multiple-star systems, not open clusters. I suspect that the isolated formation of single stars is very rare, but I'm interested in what our professional astrophysicists have to say on this topic. Sep 14 '19 at 6:19

However, it seems that the vast majority ($$>90$$%) of star clusters/associations are either born in a gravitationally unbound state or become gravitationally unbound within a few million years. The gravitationally bound open clusters, who's exemplars include the Pleiades, are comparatively rare survivors (or at least partly survived) of this "infant mortality". So, in that sense we can say no, most stars are not born in open clusters, but the likelihood is that most were born in aggregates with near neighbours that went their separate ways shortly after birth.