Key Takeaways:
- Cosmic filaments, the universe’s largest known structures, are found to spin.
- This discovery challenges the conventional thinking that only up to galaxy clusters can rotate.
- The rotation of these filaments is still a mystery, with no full theory explaining it.
- Two teams of scientists used different approaches but detected similar rotational velocities for filaments.
- The next step for researchers is to understand what makes these giant space structures spin and how they get started.
Cosmic filaments, the tendrils stretching hundreds of millions of light-years, are not just the universe’s largest known structures, but they also spin, twirling like giant corkscrews. This is a discovery made by two teams of scientists, challenging the conventional thinking that rotation ends with galaxy clusters.
These cosmic filaments, dense, slender strands of dark matter and galaxies, connect the cosmic web and channel matter toward galaxy clusters at each strand’s end. They contain most of the universe’s mass. At the instant of the Big Bang, matter didn’t rotate. It was only when stars and galaxies formed that they began to spin.
Until now, galaxy clusters were the largest structures known to rotate. “Conventional thinking on the subject said that’s where spin ends. You can’t really generate torques on larger scales,” says Noam Libeskind, a cosmologist at the Leibniz Institute for Astrophysics Potsdam in Germany.
The discovery that filaments spin, at a scale that makes galaxies look like specks of dust, presents a puzzle. “We don’t have a full theory of how every galaxy comes to rotate, or every filament comes to rotate,” says Mark Neyrinck, a cosmologist at the University of the Basque Country in Bilbao, Spain.
To test for rotation, Neyrinck and colleagues used a 3-D cosmological simulation to measure the velocities of dark matter clumps as the clumps moved around a filament. Meanwhile, Libeskind and colleagues searched for rotation in the real universe. Using the Sloan Digital Sky Survey, the team mapped galaxies’ motions and measured their velocities perpendicular to filaments’ axes.
The two teams detected similar rotational velocities for filaments despite differing approaches, Neyrinck says, an “encouraging [indication] that we’re looking at the same thing.”
The next step for researchers is to tackle what makes these giant space structures spin, and how they get started. “What is that process?” Libeskind says. “Can we figure it out?”
