Its also the cover of a Joy Division lp. There might not have been a copyright.

See: https://blogs.scientificamerican.com/sa-visual/pop-culture-p...

I saw a copyright on every version of that image I could find.

See also: https://adamcap.com/2011/05/19/the-history-of/ (mentioned in the Scientific American piece).

Pulsar data itself is likely not under copyright, but a graph of it can be under copyright protection if enough creative effort is involved. However that graph contains very little creative decision, so it would be a hard case to win if the publisher claimed ownership.

Does it cross the threshold of originality? It is just 3d line chart. Any it hardly matters what data is actually plotted, so I assume they used something random.