There’s Growing Evidence That the Universe Is Connected by Giant Structures

Lee and his colleagues studied 445 galaxies within 400 million light years of Earth, and noticed that many of the ones rotating in a direction toward Earth had neighbors that were moving toward Earth, while those that were rotating in the opposite direction had neighbors moving away from Earth.

“The observed coherence must have some relationship with large-scale structures, because it is impossible that the galaxies separated by six megaparsecs [roughly 20 million light years] directly interact with each other,” Lee said.

Lee and his colleagues suggest that the synchronized galaxies may be embedded along the same large-scale structure, which is very slowly rotating in a counter-clockwise direction. That underlying dynamic could cause the kind of coherence between the rotation of the studied galaxies and the motions of their neighbors, though he cautioned that it will take a lot more research to corroborate his team’s findings and conclusions.

While this particular iteration of weirdly synced up galaxies is novel, scientists have observed odd coherences between galaxies at even more mind-boggling distances. In 2014, a team observed curious alignments of supermassive black holes at the cores of quasars, which are ancient ultra-luminous galaxies, that stretch across billions of light years.

@physicists, what is your best guess at the explanation of these sorts of observations?

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Also, I wonder if we agree or disagree with this quote:

“One of the great things about science is that you can have a model built with thousands of pieces of data but if one thing doesn’t stick it starts to crack. That crack either has to be sealed or it’s going to bring the whole house down.”

It seems that, instead, we need a new model to move to before we let our model come down.

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Why is this? Certainly the galaxies of the Local Group interact with each other gravitationally, and this thing they’re talking about is only 10 times the distance, thus 1/100th the gravitational interaction, which is tiny but would still seem significant. Further, were these galaxies ever closer together? Why is gravity ruled out?

First of, the existence of these large scale structures is not a surprise. There have been many other evidence for them. Theoretically, they are expected, and it would have been way more puzzling had there been no evidence for them found.

Here is a recent-ish “photo”; the bright stuff are high density regions, the dark spots are “voids”:

These large scale structures can make distant galaxies cohere to each other via either:

  1. Continuous interactions with the large scale structure
  2. The large scale structure affecting the distant galaxies at their birth

The 2nd option sounds more promising, as there is weak evidence that galaxies that are perturbed after they are born are less coherent with other galaxies.

10 times the distance means that the first order torquing effect of gravity (which is responsible for example, in slowing down the Earth’s rotation), is smaller by order ~1/1000.

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Tides, in other words? Is that the interaction that’s relevant in the immediate case?

The generalization of the tides that one is used to.

At these distances, gravity is a central force. It is very hard for central forces to “torque” an object; this “generalized tides” is the biggest effect. It’s not the only effect; there are others that are caused, for example, by gravity not actually being a central force, but these are quite small at these distances for these systems and can be safely ignored.

I’m not clear on that. The observation is that the direction of rotation of some galaxy or other is correlated with the direction of movement of some of its distant neighbors. That would seem to have something to do with the origins of these galaxies. I suppose that’s your #2,

Still gravity, though, right?

Yes, that’s hypothesis #2.

Yes, almost anything that is due to these large scale structures interacting is gravitational interaction. The difference is between the galaxies torquing each other via gravity (effect is, as discussed previously, probably small) and the galaxies interacting with the large scale structure (effect can be large).

Indeed, the dominant theory is that these large scale structures are mostly dark matter, and thus pretty much only interacts gravitationally (barring small non-gravitational interactions that we expect, but so far cannot observe yet).

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