New star number presented by V and A (4)
I believe the answer is:
nova
'new star' is the definition.
(a nova might be regarded as a new star)
'number presented by v and a' is the wordplay.
'number' becomes 'no' (abbreviation).
'presented by' is a charade indicator (letters next to each other).
'and' is a charade indicator (letters next to each other).
'no'+'v'+'a'='NOVA'
(Other definitions for nova that I've seen before include "Star suddenly erupting in brightness" , "Star that ejects a cloud, thus becoming brighter" , "Suddenly expanding star" , "Star that suddenly becomes brighter for a time" , "Star that suddenly increases in brightness" .)