The most common and most likely answer to this crossword clue is the 5 plus 4 letter word BLACK HOLE
I've seen this crossword clue in The Guardian
B
L
A
C
K
H
O
L
E
Buddy explains!
The straight part
We know that "Former star" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case former star = black hole.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 BLACK HOLE mean?
BLACK HOLE noun- A place of punitive confinement; a lockup or cell; a military guardroom.
- A gravitationally domineering celestial body with an event horizon from which even light cannot escape; the most dense material in the universe, condensed into a singularity, usually formed by a collapsing massive star.
- A void into which things disappear, or from which nothing emerges; an impenetrable area or subject; an area impervious to communication.
- A place where incoming traffic is silently discarded.
- A bit bucket; a place of permanent oblivion for data.
- To redirect (network traffic, etc.) nowhere; to discard (incoming traffic).