PBS show (4)
I believe the answer is:
nova
'pbs show' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nova that I've seen before include "Sudden light increase" , "Faint star that suddenly flares into brightness and then fades again" , "Star briefly brightening" , "Star that suddenly increases in brightness" , "Star that becomes much brighter for short time" .)