Located in a room off a nondescript hallway in a building housing small experimental apparati, PPPL’s Magnetorotational Instability Experiment has been operating for over two decades. The rotating experiment helps researchers explain the behavior of vast clouds of dust, gas and other material that encircle stars and black holes and collapse to form planets and other celestial bodies.
The device is named for the source of the instability that causes the material to collapse into such bodies. The phenomenon has long been conjectured but never definitively shown to exist. Until now.
About as large as the spinning drum in a washing machine, the machine houses two nesting cylinders with the space between them currently filled with a liquid-metal alloy known as galinstan. The nested cylinders rotate at different speeds, creating regions of galinstan that rotate at different rates. This rotation mimics the differential rotation rates of dust and other material swirling in so-called accretion disks around cosmic bodies.
As the liquid in the nested cylinders turns, instabilities arise in the region between the two cylinders, just as storms develop between different masses of air on Earth. PPPL scientists have been scrutinizing these fluctuations to find evidence of the magnetorotational instability, which was thought to cause the matter in accretion disks to collapse more quickly than current models predict.
“Astrophysicists had hypothesized that turbulence in the flow of material in accretion disks could explain the formation of celestial bodies out of the material,” said Erik Gilson, the PPPL physicist in charge of the MRI experiment. “Turbulence would give the flowing material a larger viscosity and make it glom together more readily. And this is what we found.”