Rotation in the universe is a common thing. From asteroids to galaxies, objects spin on their axis and around other more massive objects. Astronomers now think that cosmic filaments, the largest known structures in the universe, also spin on an axis. The findings are reported in Nature Astronomy.
Cosmic or galaxy filaments are made of walls of gravitationally bound superclusters. They can be between 160 to 260 million light-years long and they are the threads of the cosmic web, stretching from massive node to massive node, with the notorious cosmic voids around them.
Studying such structures is far from easy. They are tenuous, so astronomers work out their presence and structure by cataloging a huge amount of galaxies – this was necessary for this study as well. The first evidence of filaments spinning came from taking data from thousands of filaments and stacking them one on top of the other.
“By mapping the motion of galaxies in these huge cosmic superhighways using the Sloan Digital Sky survey – a survey of hundreds of thousands of galaxies – we found a remarkable property of these filaments: they spin.” Lead author Dr Peng Wang, an astronomer at the Astrophysics Institute Potsdam (AIP), said in a statement.
The researchers showed this by looking at the motion of galaxies on both sides of the supposed axis of rotation. Galaxies on one side seem to be moving towards us, on the other away from us, which is what we would expect from a rotating object.
This rotation is also clearer when the filaments are being looked at edge-on, as one would expect. Also, those filaments that had the most massive collections of galaxies at each end appeared to spin fast than the others.
“Despite being thin cylinders – similar in dimension to pencils – hundreds of millions of light years long, but just a few million light years in diameter, these fantastic tendrils of matter rotate,” adds Dr Noam Libeskind, initiator of the project, also at the AIP. “On these scales the galaxies within them are themselves just specs of dust. They move on helixes or corkscrew like orbits, circling around the middle of the filament while travelling along it. Such a spin has never been seen before on such enormous scales, and the implication is that there must be an as yet unknown physical mechanism responsible for torquing these objects.”
Angular momentum is the quantity that is conserved in an object in rotational motion. It is not clear how such properties of physics arose in the early universe, but understanding how it influences the largest structures in the universe might be key to finding that out.