Breakthrough confirmation of key theory behind the formation of planets, stars and supermassive black holes

Jan. 19, 2023

A device that was originally conceived by Hantao Ji and Jeremy Goodman, faculty members in Astrophysical Sciences, in the early 2000s, was used to confirm a theory of how mass is driven inward in so-called accretion disks to form planets, stars, and supermassive black holes.  Since the early 1990’s it has been hypothesized that in the accretion disks around planets, stars, and black holes, mass flows radially inward while angular momentum flows radially outward due to the action of the magnetorotational instability (MRI), which is mediated by loops of magnetic field that stretch and apply torques between adjoining radial regions.  A crucial aspect of the theory is that it applies in electrically conducting media provided that the angular rotation rate decreases toward larger radius. This theoretical idea has finally been demonstrated experimentally, using an apparatus that have been developed at Princeton Plasma Physics Laboratory (PPPL) over the past two decades.  The device has an inner and outer cylinder, with the space between them filled with a liquid-metal alloy.  The cylinders and three end-caps rotate at different speeds, mimicking the differential rotation of accretion disks in astrophysical systems.  

 “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 physicist in charge of the MRI experiment.

“Turbulence would give the flowing material a larger viscosity…and this is what we found.” “This has remained theoretical until now,” said physicist Yin Wang, lead author of two recent papers, one in September in Physical Review Letters (PRL) and a Nature Communications paper published in August that details the combined experimental, numerical, and theoretical confirmation. “This is great news,” said astrophysicist Steven Balbus, Oxford University, who co-developed the MRI theory with colleague John Hawley. “To now be able to study this in the laboratory is a wonderful development, both for astrophysics and for the field of magnetohydrodynamics more generally.”

Click here to learn more about how the MRI works.

Click here to learn more about the history of the experiment.

Click here for more information on the discovery.

Congratulations to the team on this breakthrough!

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