Sorry.

Things do not move through space, they move relative to each other.

Light moves through space at light speed. Light speed is independent of the velocity of any observer.

tell that to "the Sky at Night" presenters. They explain by analogy.

I watched that thanks.
It was about detecting non-ionised gas.
It was not about, "Pulsars were so intenses (and focused) they reacted with baryons." which makes no sense.