The great attractor is probably a very massive galaxy cluster located where we can't see it behind Milky Way dust clouds. It is the explanation for why relatively local galaxies are having their velocities changed in that general direction.

There isn't a specific physical reason that it couldn't be explained by a large collection of purely non-baryonic dark matter, but so far we haven't ever seen something like that, so the odds seem pretty low.

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Forming opinions as we speak