2006/11/01 by Hantao Ji, M. J. Burin, Michael J. Burin +3 · 9 citations
Physics and Astronomy · #Accretion (finance) #Angular momentum #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Classical mechanics #Magnetic field #Magnetohydrodynamics #Magnetorotational instability #Mechanics #Physics #Stellar, planetary, and galactic studies #Turbulence #astro-ph #physics.flu-dyn
paper · pdf · doi:10.1038/nature05323
published as Nature 444 (2006) 343 · 12 pages and 4 figures. To be published in Nature on November 16, 2006, available at http://www.nature.com/nature/journal/v444/n7117/abs/nature05323.html
openalex publication_date 2006/11/01 · arxiv created 2006/11/15 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The most efficient energy sources known in the Universe are accretion disks. Those around black holes convert 5 -- 40 per cent of rest-mass energy to radiation. Like water circling a drain, inflowing mass must lose angular momentum, presumably by vigorous turbulence in disks, which are essentially inviscid. The origin of the turbulence is unclear. Hot disks of electrically conducting plasma can become turbulent by way of the linear magnetorotational instability. Cool disks, such as the planet-forming disks of protostars, may be too poorly ionized for the magnetorotational instability to occur, hence essentially unmagnetized and linearly stable. Nonlinear hydrodynamic instability often occurs in linearly stable flows (for example, pipe flows) at sufficiently large Reynolds numbers. Although planet-forming disks have extreme Reynolds numbers, Keplerian rotation enhances their linear hydrodynamic stability, so the question of whether they can be turbulent and thereby transport angular momentum effectively is controversial. Here we report a laboratory experiment, demonstrating that non-magnetic quasi-Keplerian flows at Reynolds numbers up to millions are essentially steady. Scaled to accretion disks, rates of angular momentum transport lie far below astrophysical requirements. By ruling out purely hydrodynamic turbulence, our results indirectly support the magnetorotational instability as the likely cause of turbulence, even in cool disks.