Spin-Induced Disk Precession in Sagittarius A*

Details Spin-Induced Disk Precession in Sagittarius A* Spin-Induced Disk Precession in Sagittarius A*

2005-07-12

arxiv.org/abs/astro-ph/0507302v2

Astrophys.J.635:336-340,2005

Astronomy and Astrophysics

Astrophysics

14 pages, 3 figures; small changes to sections 2.1 and 3; accepted for publication in ApJ

Scientific paper

10.1086/496947

In Sgr A* at the Galactic center, by far the closest and easiest supermassive black hole we can study, the observational evidence is increasingly pointing to the presence of a compact, hot, magnetized disk feeding the accretor. In such low-Mach-number plasmas, forces arising, e.g., from pressure gradients in the plasma, can altogether negate the warping of disks around Kerr black holes caused by the Bardeen-Petterson effect and can lead to coherent precession of the entire disk. In this Letter, we present for the first time highly detailed 3D SPH simulations of the accretion disk evolution in Sgr A*, guided by observational constraints on its physical characteristics, and conclude that indeed the Bardeen-Petterson effect is probably absent in this source. Given what we now understand regarding the emission geometry in this object, we suggest that a ~ 50-500-day modulation in Sgr A*'s spectrum, arising from the disk precession, could be an important observational signature; perhaps the ~ 106-day period seen earlier in its radio flux, if confirmed, could be due to this process. On the other hand, if future observations do not confirm this long modulation in Sgr A*'s spectrum, this would be an indication that either the disk size or orientation is very different from current estimates, or that the black hole is not spinning at all (unlikely), or that our current understanding of how it produces its radiative output is incorrect.

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