A dead planet is discovered.
It died with the death of it’s sun.
The sun winking out is correlated in time to have occured at the same time as the birth of Jesus of Nazareth.
Thus the star of Bethlehem is the distant sun dying.
The point of the story, if I remember correctly, was to juxtapose the arrival of the saviour with the death of a world not too dissimilar to earth.
Can anyone help me remember the author of this short story? Ta!