Spin-induced disk precession in the supermassive black hole at the Galactic center

Siming Liu, Fulvio Melia

Research output: Contribution to journalArticle

46 Citations (Scopus)

Abstract

Sagittarius A* is a compact radio source at the Galactic center that is thought to be the radiative manifestation of a 2.6 × 106 M supermassive black hole. At least a portion of its spectrum-notably the millimeter/submillimeter "bump"-appears to be produced within the inner portion (r < 10rs) of a hot, magnetized Keplerian flow, whose characteristics are also consistent with the ∼10% linear polarization detected from this source at millimeter wavelengths. (The Schwarzschild radius, rs, for an object of this mass M is 2GM/c 2 ≈ 7.7 × 1011 cm, or roughly 1/20 AU.) The recent detection of a 106 day cycle in Sgr A*'s radio variability adds significant intrigue to this picture since it may signal a precession of the disk induced by the spin a of the black hole. The dynamical timescale near the marginally stable orbit around an object with this mass is ≈20 minutes. Thus, since the physical conditions associated with the disk around Sgr A* imply rigid-body rotation, a precession period of 106 days may be indicative of a small black hole spin if the circularized flow is confined to a region ∼30rs, for which a ≈ (M/10)(ro/30r s)5/2. The precession of a larger structure would require a bigger black hole spin. We note that a small value of a/M (<0.1) would be favored if the nonthermal (∼1-20 cm) portion of Sgr A*'s spectrum is powered with energy extracted via a Blandford-Znajek type of process, for which the observed luminosity would correspond to an outer disk radius ro ∼ 30rs. Such a small disk size is also suggested by earlier hydrodynamical simulations and is implied by Sgr A*'s spectral and polarimetric characteristics.

Original languageEnglish (US)
JournalAstrophysical Journal
Volume573
Issue number1 II
DOIs
StatePublished - Jul 1 2002

Fingerprint

precession
radio
radii
flow characteristics
rigid structures
polarization
linear polarization
wavelength
timescale
luminosity
orbits
cycles
simulation
energy
wavelengths

Keywords

  • Accretion, accretion disks
  • Black hole physics
  • Galaxy: center
  • Gravitation radiation mechanisms: nonthermal
  • Relativity

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Spin-induced disk precession in the supermassive black hole at the Galactic center. / Liu, Siming; Melia, Fulvio.

In: Astrophysical Journal, Vol. 573, No. 1 II, 01.07.2002.

Research output: Contribution to journalArticle

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abstract = "Sagittarius A* is a compact radio source at the Galactic center that is thought to be the radiative manifestation of a 2.6 × 106 M⊙ supermassive black hole. At least a portion of its spectrum-notably the millimeter/submillimeter {"}bump{"}-appears to be produced within the inner portion (r < 10rs) of a hot, magnetized Keplerian flow, whose characteristics are also consistent with the ∼10{\%} linear polarization detected from this source at millimeter wavelengths. (The Schwarzschild radius, rs, for an object of this mass M is 2GM/c 2 ≈ 7.7 × 1011 cm, or roughly 1/20 AU.) The recent detection of a 106 day cycle in Sgr A*'s radio variability adds significant intrigue to this picture since it may signal a precession of the disk induced by the spin a of the black hole. The dynamical timescale near the marginally stable orbit around an object with this mass is ≈20 minutes. Thus, since the physical conditions associated with the disk around Sgr A* imply rigid-body rotation, a precession period of 106 days may be indicative of a small black hole spin if the circularized flow is confined to a region ∼30rs, for which a ≈ (M/10)(ro/30r s)5/2. The precession of a larger structure would require a bigger black hole spin. We note that a small value of a/M (<0.1) would be favored if the nonthermal (∼1-20 cm) portion of Sgr A*'s spectrum is powered with energy extracted via a Blandford-Znajek type of process, for which the observed luminosity would correspond to an outer disk radius ro ∼ 30rs. Such a small disk size is also suggested by earlier hydrodynamical simulations and is implied by Sgr A*'s spectral and polarimetric characteristics.",
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