Hydrodynamic turbulence cannot transport angular momentum effectively in astrophysical disks

Area of Science:

• Astrophysics
• Plasma Physics
• Fluid Dynamics

Background:

• Accretion disks, particularly around black holes, are highly efficient energy sources, converting significant rest-mass energy to radiation.
• Turbulence in accretion disks is essential for angular momentum transport, enabling inflowing mass to lose momentum.
• The origin of turbulence in cool, poorly ionized disks like protostellar systems remains unclear, as the magnetorotational instability may not be active.

Purpose of the Study:

• To investigate the potential for hydrodynamic turbulence in non-magnetic, quasi-Keplerian flows relevant to cool accretion disks.
• To experimentally determine the rate of angular momentum transport in such flows and compare it to astrophysical requirements.

Main Methods:

• Conducted laboratory experiments simulating non-magnetic, quasi-Keplerian flows at high Reynolds numbers (up to millions).
• Measured angular momentum transport rates in these controlled flow conditions.

Main Results:

• Observed that the non-magnetic quasi-Keplerian flows remained essentially steady, even at high Reynolds numbers.
• Calculated angular momentum transport rates were significantly lower than those required for astrophysical accretion disks.
• Demonstrated that purely hydrodynamic turbulence is insufficient to explain the observed phenomena in these flows.

Conclusions:

• Hydrodynamic turbulence does not appear to be the primary mechanism for angular momentum transport in non-magnetic, quasi-Keplerian flows.
• These findings indirectly support the magnetorotational instability as the likely source of turbulence in cool accretion disks.
• The study highlights the importance of magnetic fields in driving turbulence and accretion processes in astrophysical disks.