Is it necessary that only a site column can be crawled and have a crawled property associated with it.

Can I have a custom column in a list and expect it to be available as crawled property.

Also, can I map multiple site columns to a single Managed property.

**Edit:**

The answer raises another question. What will happen if I have a custom column in 2 different lists(not created using site columns) with the same name. Is there a syntax for this naming convention?