LogoLogo
  • Bio
  • Fyzika
  • V médiích
  • Fotografie
  • Výstavy
  • Kontakt

    Marginally stable thick discs with gradient inversion of orbital velocity measured in locally non-rotating frames. A mechanism for excitation of oscillations in accretion discs?

    Zdeněk Stuchlík · 01 prosince, 2004 · Fyzika · 0 comments
    0

    Publication date: Dec 2004

    Abstract:
    Aschenbach [Aschenbach, B. (2004). Measuring mass and angular momentum
    of black holes with high-frequency quasi-periodic oscillations.
    Astronomy and Astrophysics, 425:1075-1082] has shown that in Kerr
    black-hole spacetimes with rotation parameter a>0.9953, the Keplerian
    orbital velocity measured in locally non-rotating frames (LNRF) has a
    positive radial gradient in a small region in the vicinity of the event
    horizon and proposed that excitation of oscillations in Keplerian thin
    discs can be related to this fact. Similarly, we show that in the
    equatorial plane of marginally stable thick discs (with uniformly
    distributed specific angular momentum ℓ(r,θ)=const) the
    orbital velocity relative to the LNRF has a positive radial gradient in
    the vicinity of black holes with a>0.99979. The change of sign of the
    velocity gradient occurs just above the centre of the thick toroidal
    discs, in the region where stable circular geodesics of the Kerr
    spacetime are allowed. Therefore, the same mechanism as in the Keplerian
    discs could trigger oscillations in thick discs, but the rotational
    parameter of the Kerr spacetime must be much closer to the extreme-hole
    state with a=1. The global character of the phenomenon is given in
    terms of topology changes of the von Zeipel surfaces (equivalent to
    equivelocity surfaces in the tori with ℓ (r,θ)=const).
    Toroidal von Zeipel surfaces exist around the circle corresponding to
    the minimum of the equatorial LNRF velocity profile, indicating a
    possibility of development of some vertical instabilities in those parts
    of marginally stable tori with positive gradient of the LNRF velocity.

    Authors:
    Stuchlík, Zdeněk; Slaný, Petr; Török, Gabriel;

    http://adsabs.harvard.edu/abs/2004ragt.meet..239S

      Facebook   Pinterest   Twitter

    Leave a Comment! Zrušit odpověď na komentář

    You must be logged in to post a comment.
    Archivy
    Copyright © 2024 Zdeněk Stuchlík