I have a general question about how topic tags become associated with a vote-based badge. For instance, if I receive 100 upvotes on answers for at least 20 non-community wiki answers with the associated the tag astrophysics, then I get a bronze astrophysics badge.
In contrast, if I get (currently) 103 upvotes on 31 non-community answers associated with the solar-wind tag, I see no bronze badge.
How are tag badges created/formed for a given tag?