Hundreds of billions of galaxies spiral, ring-shaped, looped, and others make up our universe. Sometimes, despite their differences and the vast distances between them, galaxies move together, as if an unseen force connects them
Finding such connections suggests the presence of large-scale structures, scientists say. Made of hydrogen gas and dark matter, they are the filaments, sheets, and knots that link galaxies together. En masse, they are a far-reaching network of cosmic connections.
However, we know very little about the dynamics of the structures. Scientists are eager to learn more, as the structures may change some fundamental ideas we hold about the universe.
'Thats actually the reason why everybody is always studying these large-scale structures,' Noam Libeskind, a cosmographer at the Leibniz-Institute for Astrophysics, tells Vice. 'Its a way of probing and constraining the laws of gravity and the nature of matter, dark matter, dark energy, and the universe.'
Synchronicity in spite of distances
Each galaxy is part of a gravitationally bound cluster, a local group that contains a few other galaxies. The local group is, in turn, a part of a supercluster. So, for example, the Milky Way is part of a local group that contains several dozen galaxies, and the local group is part of the Virgo supercluster, that has more than 10,000 galaxies.
The effect a galaxy may have on another on the local scale is well-understood. However, how galaxies are linked to others at distances too great to be explained by gravitation remains unknown.
A recentstudy publishedin The Astrophysical Journaldescribes 445 galaxies rotating in sync with the motions of other galaxies located at a distance of tens of millions of light years away.
'This discovery is quite new and unexpected,' says Korea Astronomy and Space Science Institutes astronomerJoon Hyeop Lee, the lead author of the study. 'I have never seen any previous report of observations or any prediction from numerical simulations exactly related to this phenomenon.'
Leeand his team looked at galaxies within 400 million light years of Earth, finding that the ones rotating toward our home planet had neighbors that were moving toward it as well. Similarly, those rotating away fromEarthhad neighbors moving away from Earth, too.
'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,' Leesays.
The conclusion the team made was that there must be a slowly rotating large-scale structure to explain the synchronous rotation and movement of the galaxies.
And while the idea is new, it has been observed before: A 2014 study discovered alignment of supermassive black holes at the cores of quasars that stretch billions of light years. The discovery, published in Astronomy & Astrophysics, included observations of synchronicity by using the Very Large Telescope in Chile. Analyzing the recordings from the polarization of light from nearly 100 quasars, the research team, led by University of Liges Damien Hutsemkers, reconstructed the alignment of the black holes, finding that the rotation axes of 19 quasars were parallel, even though they had been separated by a few billion light years.
'Galaxy spin axes are known to align with large-scale structures such as cosmic filaments, but this occurs on smaller scales,' Hutsemkers says. 'However, there is currently no explanation why the axes of quasars are aligned with the axis of the large group in which they are embedded.'
Will new studies overturn old theories?
If the large-scale structures exist, then the cosmological principle one that states that the universe is basically uniform and homogeneous is false. The existence of such structures would counter that principle. Even so, Hutsemkers and his team warned that more research is needed to seriously put a dent on the long-standing belief. 'Other similar structures are needed to confirm a real anomaly,' he says.
One of the difficulties astronomers face is the limitations of the observational techniques, although future radio telescopes such as the Square Kilometer Array may help. 'As far as large-scale alignments are concerned, we are essentially waiting for more data,' Hutsemkers says. 'Such studies are statistical and a step forward would require a large amount of polarization data, not easy to gather with current instrumentation.'
Another issue is the way in which dwarf galaxies seem to align around larger host galaxies. This is a problem for the CDM model, which provides the theoretical timeline of the universe since its inception. Simulations under the model show that the satellite galaxies should be distributed randomly and yet they are not. Such neatly synced galaxies have been found to orbit the Milky Way, Andromeda, and Centaurus A, with the latest discovery published in Science in 2018.
The latter has also led scientists to admit that the CDM model has serious faults.
'At the moment, we have observed this at the three closest galaxies,' Oliver Mller, lead author of the 2018 study, says. 'Of course, you can always say that its only three, so its not statistical yet. But it shows that every time we have good data, we find it, so it could be universal.'
A 2015 study suggested a way to bring together the CDM model with the new findings, suggesting that cosmic web filaments might be guiding the synced galaxies. '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 doesnt stick it starts to crack,' explains lead author Libeskind. 'That crack either has to be sealed or its going to bring the whole house down.'
Next-generation technology offers hope
The consensus among scientists is that more research is needed, with much of the hope placed upon the data that will come from the next-generation observatories. The synced dwarf galaxies and the alignment of galaxies across millions of light years seem to hold clues to the mysteries of the large-scale structure of the universe, of forces that we do not yet understand, or both.
'What I really like about this stuff is just that we are still at the pioneering phase,' says Mller. 'Thats super exciting.'
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The Universe Is Laced with Giant Structures Connecting Distant Galaxies - Asgardia Space News