Hydrogen emitted originally by a pulse star? (8)
I believe the answer is:
hexagram
'star?' is the definition.
(hexagram is a kind of star)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for hexagram that I've seen before include "Six-pointed star made from two intersecting triangles" , "Six-lined figure" , "Figure of six lines" , "Star-shaped figure" .)