Extragalactic nebula and Great Attractor

Extragalactic nebula noun - (astronomy) a collection of star systems; any of the billions of systems each having many stars and nebulae and dust.

Great Attractor and extragalactic nebula are semantically related. In some cases you can replace phrase "Great Attractor" with "Extragalactic nebula", this phrases are similar.

Great Attractor noun - A massive grouping of galaxies in the direction of Centaurus and Hydra whose gravitational attraction is believed to cause deviations in the paths of other galaxies.

Extragalactic nebula and Great Attractor are semantically related. You can use "Extragalactic nebula" instead a noun phrase "Great Attractor".