The most common and most likely answer to this crossword clue is the 8 letter word BINARIES
I've seen this crossword clue in The Guardian
B
I
N
A
R
I
E
S
Buddy explains!
The straight part
We know that "Stellar couples" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stellar couples = binaries.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 BINARIES mean?
BINARIES noun- A thing which can have only (one or the other of) two values.
- The bijective base-2 numeral system, which uses only the digits 0 and 1.
- An executable computer file.
- A satellite system consisting of two stars or other bodies orbiting each other.