The canon "answer" is that the Force itself caused Anakin to be conceived w/o explanation as to the biophysics involved. IMO, this has been ASSUMED since Shmi simply declares in Episode I that Anakin had no father, that she'd become pregnant w/o benefit of intercourse (poor Shmi, for all that grief and work she deserved at least one night of fun). This echoes the 'miraculous' conception of Jesus Christ. (BTW, it should be noted that some sects, like Mormons, believe that Jesus is literally the Son of God but do not speculate as to HOW that was accomplished, e.g., intercourse didn't necessarily have had to happen). Likewise, following the script of Episode I doesn't preclude a biological father for Anakin, but also gives no clues as to the identity of said father.

The canon "answer" is that the Force itself caused Anakin to be conceived w/o explanation as to the biophysics involved. IMO, this has been ASSUMED since Shmi simply declares in Episode I that Anakin had no father, that she'd become pregnant w/o benefit of intercourse (poor Shmi, for all that grief and work she deserved at least one night of fun). This echoes the 'miraculous' conception of Jesus Christ. Likewise, following the script of Episode I doesn't preclude a biological father for Anakin, but also gives no clues as to the identity of said father.