Small molecules, spinning tops and figure skaters all have something in common – they all rotate.
What is different is scale. The spin of a figure skater is some 10 billion times larger than that of an atom. Zoom out again by the same factor, and measurements start reaching tens of thousands of light years, a distance stretching almost half way across our Milky Way galaxy. It spins too – incredibly slowly – taking hundreds of millions of years to complete a full rotation.
Edinburgh researchers, working with colleagues in Spain and Mexico, have recently measured the rotation of objects still hundreds to thousands of times larger than the Milky Way. The structures – known as intergalactic filaments – are thought to be the longest rotating things in the Universe.
The discovery was made by a team including Qianli Xia and Yan-Chuan Cai from the School of Physics and Astronomy. Together with Mark Neyrinck from the University of the Basque Country and Miguel Aragon from the National Autonomous University of Mexico, they used sophisticated computer simulations to measure the rotation of these unimaginably vast structures, which are tens of millions of light-years long and millions of light-years thick.
You spin me right round
The team analysed computer-generated Universes with properties closely resembling the observed Universe, produced by supercomputers running for many months.
From this constellation of data, the team was able to identify more than 30 thousand filaments, each measuring more than 20 million light-years in length. Each filament typically connected a pair of galaxies in the simulation and, by aligning the positions of these, the team was able to determine that these intergalactic filaments were spinning
“The way these incredibly long strings of matter spin is neither like a tornado vortex – which is fastest at its centre – nor like that of a fixed car axle, but somewhere in between”, says Dr Cai. “Filaments provide an environment for the growth of galaxies, and we’re learning more and more about how they influence the properties of galaxies within them. The way galaxies spin is known to be connected to the direction of the filament they are found in, so discovering this new physical feature of filaments may prompt scientists to look more closely at how it might affect the rotation of galaxies.”
If the time it takes for a galaxy like the Milky Way to rotate seems long, for an intergalactic filament it is unfathomable. In fact, the team predicted that most of them have yet to complete a full rotation since they formed billions of years ago. Despite this, their vast size means that the speed at which they spin is staggeringly fast by human standards, generally rotating at hundreds of thousands of kilometres an hour.
News of the team’s remarkable theoretical prediction in 2020 prompted another group of researchers to look for intergalactic filaments in the real Universe. Using the most detailed 3D maps of the Universe ever created – the Sloan Digital Sky Survey – the team, led by researchers from the Leibniz Institute for Astrophysics Potsdam, Germany, found that many filaments do indeed rotate, confirming the work of Xia, Cai, Neyrinck and Aragon.
“The observational team found that many filaments stretching across the sky had galaxies moving toward us on one side, and galaxies moving away on the other. The simplest explanation for this? The filaments are rotating”, says Dr Qianli Xia. “One cannot help being in awe thinking about the discoveries that we as a research community are making on such vast scales in the Universe we live in.”
Right round like a record
Zoom back in again. The inspiration for measuring the rotation of intergalactic filaments came from an origami model developed by Mark Neyrinck from the University of the Basque Country. In the hand-held model, if a filament is linked to a rotating galaxy – as the team’s simulations reveal they typically are – it must rotate.
“It is amazing that this model based on origami twist folds bears any resemblance to the way filaments rotate in the real Universe,” says Neyrinck. “I’m not aware of a better example of art enabling scientific discovery.”
Picture credits: space – Getty/den-belitsky; figure skater – Getty/Simonkr