Mechanic in a star that's collapsing (7)
I believe the answer is:
artisan
'mechanic' is the definition.
(I've seen this before)
'in a star that's collapsing' is the wordplay.
'that's collapsing' indicates anagramming the letters.
'in'+'a'+'star'='inastar'
'inastar' anagrammed gives 'ARTISAN'.
(Other definitions for artisan that I've seen before include "crafty person?" , "Skilled worker at craft or trade" , "Skilled workman" , "Egypt peninsula; holy Mount" , "Technician" .)