The most common and most likely answer to this crossword clue is the 4 letter word NOVA
N
O
V
A
More clues leading to the result NOVA
Buddy explains!

The straight part
We know that "Bright star" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bright star = nova.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does NOVA mean?
NOVA noun- Any sudden brightening of a previously inconspicuous star.