Backing America to create a proven star (9)
I believe the answer is:
supernova
'star' is the definition.
(supernova is a kind of star)
'backing america to create a proven' is the wordplay.
'backing' says the letters should be written backwards.
'america' becomes 'us' (abbreviation for the United States**).
'to create' indicates anagramming the letters.
'us' reversed gives 'su'.
'a'+'proven'='aproven'
'aproven' anagrammed gives 'pernova'.
'su'+'pernova'='SUPERNOVA'
(Other definitions for supernova that I've seen before include "The sort of star" , "Star that explodes and becomes extremely luminous" , "cosmic explosion" , "it puts an end to a starry career" , "Star in decline" .)