How should the number of subjects for participation in a qualitative study be determined?

I believe the answer is: Data are collected from new subjects until no new information is generated.

In a qualitative study, the researchers would not use any of numerical value to measure the result of the study. Because of this, they need to make sure that they include all possible variants from different subjects until new variants is no longer exist in their collection of subjects.

White dwarf is very hot, but also very small and that is why it may appear dim.