Track celebrity's heavenly body (3,4)
I believe the answer is:
dog star
'heavenly body' is the definition.
(Dog Star is an example)
'track celebrity's' is the wordplay.
'track' becomes 'dog' (synonyms).
'celebrity's' becomes 'star' (I've seen this before).
'dog'+'star'='DOG-STAR'
(Other definitions for dog star that I've seen before include "What may not be seen on cloudy night" , "Part of 8 [CANIS MAJOR]" , "Night light" , "clearly visible shiner" , "Canine constellation" .)