Note there are seven rays within a flat circle.
I suspect the use by romans of circles to outline images within mosaics may have contributed to the development of halos.
Now some Byzantine mosaics show Christ with a halo with 3 rays but these date to several centuries later so it is possible they are an independent development?
Here's one of them from the Hagia Sophia :
So rayed halos worn by Hellenistic Sun gods and Kings ! (See prior post)
But how direct was the influence on Christian and Byzantine art?
The earliest depictions of Christ usually use the Good Shepherd image but there is this Roman wall painting ...
Its as much a circle as a halo and may have been used more to emphasize that this figure is Christ?
Finally a classic 4th century Byzantine mosaic :
By the way this one was "restored" in the 19th century so possibly the colors have been altered.
My point is Christian halos differ from Pagan solar halos and while those artists probably saw pagan sun god images the earliest halos was more usually flat.
Those rayed halos you see in Rocco and Baroque devotional art?
A much later borrowing!
There is a continuum from pagan to byzantine art but its one of continuous development inspired by classical ideas to create new forms.