Galaxies seem to be communicating with each other across vast distances never thought possible before, putting the cosmological principle into question again.
These gravitationally bound structures consisting of gas, dust and trillions of stars exist in the trillions. Most observed galaxies are spiral galaxies like our very own Milky Way, with others being elliptical, lenticular or irregular. The formation and evolution of a galaxy is generally revealed in galactic kinematics, particularly the rotation which is constrained by the conservation of angular momentum. Through studying the rotation of galaxies, scientists can thus infer how the galaxy was formed and how it evolved. Did it form from a rotating dust cloud? Did it evolve as a merger?
As would be expected, galactic behaviour – including its rotation – is influenced by that of its neighbours. However, in a recent report, Korean scientists Joon Hyeop Lee and colleagues presented observational evidence that the rotational direction of a galaxy tends to be coherent with the average motion of its nearby neighbours within 1 mega parsec (Mpc) – that’s 3 million light years or 20 million trillion miles. This is way beyond the expected effects of gravity.
Intrigued, Lee and his colleagues wanted to see just how far this coherency stretched. Utilizing data from the Calar Alto Legacy Integral Field Area survey (CALIFA) – an astronomical project utilizing the Calar Alto observatory in Spain to map 600 galaxies – they mapped the velocity distribution of ‘neighbour’ galaxies within 15 Mpc from the CALIFA galaxies.
A composite of panels depicting maps of some of the properties of galaxies obtained from CALIFA data.
Remarkably, they found that within distances of several mega parsecs the velocity profiles showed unexpectedly strong evidence of the dynamical coherence between the rotation of the CALIFA galaxies and their neighbours. Small scale coherences have been explained in terms of an entropic force – more on that can be read here – but what could be causing this large-scale coherence?
In a recent paper presenting these results, Lee and his team contemplated that question and suggested that a possible relationship exists between the long-term motion of a large-scale structure and the rotations of galaxies in it.
Axis alignments with large-scale structures such as cosmic filaments have been observed before. For example, in 2014 the axis alignments of a significant number of quasars were found to be parallel. Read more here.
However, any correlation in axis alignment over such large distance violates the cosmological principle, which states that we live in a homogeneous and isotropic universe.
To add fuel to the fire, in 2018 a team of scientists found that a significant number of dwarf galaxies followed a coherent velocity pattern aligned with the long axis of their host galaxy, as opposed to orbiting randomly as predicted by the cosmological model. Read more here.
More and more of these mysterious coherences are being observed, putting the cosmological principle into question.