A Possible Rossby Wave Instability Origin for the Flares in Sagittarius A*
Abstract
In recent years, near-IR and X-ray flares have been detected from the Galaxy's central radio point source, Sagittarius A* (Sgr A*), believed to be an ~3×106 Msolar supermassive black hole. In some cases, the transient emission appears to be modulated with a (quasi-)periodic oscillation (QPO) of ~17-20 minutes. The implied ~3rS size of the emitter (where rS≡2GM/c2 is the Schwarzschild radius) points to an instability-possibly induced by accretion-near the marginally stable orbit (MSO) of a slowly spinning object. But Sgr A* is not accreting via a large, ``standard'' disk; instead, the low-density environment surrounding it apparently feeds the black hole with low angular momentum clumps of plasma that circularize within ~(10-300)rS and merge onto a compact, hot disk. In this Letter, we follow the evolution of the disk following such an event, and we show that a Rossby wave instability, particularly in its magnetohydrodynamic (MHD) form, grows rapidly and produces a period of enhanced accretion lasting several hours. Both the amplitude of this response and its duration match the observed flare characteristics rather well.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2006
- DOI:
- 10.1086/499806
- arXiv:
- arXiv:astro-ph/0511520
- Bibcode:
- 2006ApJ...636L..33T
- Keywords:
-
- Accretion;
- Accretion Disks;
- Black Hole Physics;
- Galaxy: Center;
- Instabilities;
- Magnetohydrodynamics: MHD;
- Plasmas;
- Astrophysics
- E-Print:
- Accepted for publication in ApJ Letters