Mhd simulations of accretion onto Sgr A*: Quiescent fluctuations, outbursts, and quasiperiodicity

Chi Kwan Chan, Siming Liu, Christopher L. Fryer, Dimitrios Psaltis, Feryal Zel, Gabriel Rockefeller, Fulvio Melia

Research output: Contribution to journalArticle

39 Scopus citations

Abstract

High-resolution observations of Sgr A* have revealed a wide variety of phenomena, ranging from intense rapid flares to quasi-periodic oscillations (QPOs), making this object an ideal system to study the properties of low luminosity accreting black holes. In this paper, we use a pseudospectral algorithm to construct and evolve a three-dimensional magnetohydrodynamic (MHD) model of the accretion disk in Sgr A*. Assuming a hybrid thermal-nonthermal emission scheme and calibrating the parameters by observations, we show that the MHD turbulence in the environment of Sgr A* can by itself only produce factor two fluctuations in luminosity. These fluctuations cannot explain the magnitude of flares observed in this system. However, we also demonstrate that external forcing of the accretion disk, which may be generated by the "clumpy material" raining down onto the disk from the large-scale flow, do produce outbursts qualitatively similar to those observed by XMM-Newton in X-rays and by ground-based facilities in the near infrared. Strong, but short-term QPOs emerge naturally in the simulated light curves. We attribute these to nonaxisymmetric density perturbations that emerge as the disk evolves back toward its quiescent state.

Original languageEnglish (US)
Pages (from-to)521-534
Number of pages14
JournalAstrophysical Journal
Volume701
Issue number1
DOIs
StatePublished - Jan 1 2009

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Keywords

  • Accretion, accretion disks
  • Black hole physics
  • Galaxy: center
  • Instabilities
  • MHD
  • Relativity

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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