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Black Hole

Lensing of space time around a black hole. At Oxford we study black holes observationally and theoretically on all size and time scales - it is some of our core work.

Credit: ALAIN RIAZUELO, IAP/UPMC/CNRS. CLICK HERE TO VIEW MORE IMAGES.

Prof Steven Balbus FRS, FInstP

Emeritus Savilian Professor

Research theme

  • Astronomy and astrophysics

Sub department

  • Astrophysics

Research groups

  • Pulsars, transients and relativistic astrophysics
steven.balbus@physics.ox.ac.uk
  • About
  • Publications

The plunging region of a thin accretion disc around a Schwarzschild black hole

Monthly Notices of the Royal Astronomical Society Oxford University Press 542:1 (2025) 377-390

Authors:

Jake Rule, Andrew Mummery, Steven Balbus, James M Stone, Lizhong Zhang

Abstract:

A set of analytic solutions for the plunging region thermodynamics has been developed recently under the assumption that the fluid undergoes a gravity-dominated geodesic plunge into the black hole. We test this model against a dedicated 3D global general relativistic magnetohydrodynamics simulation of a thin accretion disc around a Schwarzschild black hole using the code athenak . Provided that we include the effects of non-adiabatic heating (plausibly from grid-scale magnetic dissipation), we find excellent agreement between the analytic model and the simulated quantities. These results are particularly important for existing and future electromagnetic black hole spin measurements, many of which do not include the plunging fluid in their emission modelling. This exclusion typically stems from the assumption of a zero-stress boundary condition at the innermost stable circular orbit (ISCO), forcing all thermodynamic quantities to vanish. Instead, we find a non-zero drop in the angular momentum over the plunging region, which is consistent with both prior simulations and observations. We demonstrate that this stress is small enough for the dynamics of the fluid in the plunging region to be well-described by geodesic trajectories, yet large enough to cause measurable dissipation near to the ISCO – keeping thermodynamic quantities from vanishing. In the plunging region, constant -disc models are a physically inappropriate framework.
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Determining the difference between local acceleration and local gravity: applications of the equivalence principle to relativistic trajectories

American Journal of Physics American Association of Physics Teachers 92:6 (2024) 444-449

Abstract:

We show by direct calculation that the common equivalence principle explanation for why gravity must deflect light is quantitatively incorrect by a factor of three in Schwarzschild geometry. It is, therefore, possible, at least as a matter of principle, to tell the difference between local acceleration and a true gravitational field by measuring the local deflection of light. We calculate as well the deflection of test particles of arbitrary energy and construct a leading-order coordinate transformation from Schwarzschild to local inertial coordinates, which shows explicitly how the effects of spatial curvature manifest locally for relativistic trajectories of both finite and vanishing rest mass particles.
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The dynamics of accretion flows near to the innermost stable circular orbit

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 529:2 (2024) 1900-1916

Authors:

Andrew Mummery, Francesco Mori, Steven Balbus
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Testing theories of accretion and gravity with super-extremal Kerr discs

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 527:3 (2023) 5956-5973

Authors:

Andrew Mummery, Steven Balbus, Adam Ingram
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Fundamental scaling relationships revealed in the optical light curves of tidal disruption events

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 527:2 (2023) 2452-2489

Authors:

Andrew Mummery, Sjoert van Velzen, Edward Nathan, Adam Ingram, Erica Hammerstein, Ludovic Fraser-Taliente, Steven Balbus
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