Formation of massive star clusters

3 problems

• What produces the spin spread behind extended cluster turnoffs?

  Partially resolved

  In star clusters a few hundred million to two billion years old, the stars that are just exhausting their core hydrogen do not lie on one thin line in the color-brightness diagram. This is now mostly blamed on stars spinning at different rates, but why some stars spin slowly and others fast is unclear.

• Are globular clusters survivors of young massive clusters in early galaxies?

  Contested

  The James Webb Space Telescope sees very dense young star clusters in galaxies less than a billion years after the Big Bang. Whether today's globular clusters are the survivors of such clusters, or needed special conditions to form, is not known.

• Origin of multiple stellar populations in globular clusters

  Open

  Most old star clusters contain two or more groups of stars with different chemical makeup, as if part of the cluster formed from gas polluted by earlier stars. The proposed polluters cannot make enough polluted gas unless the cluster was once ten or more times heavier.