Astronomy and Astrophysics – Astrophysics
Scientific paper
1997-06-11
Astrophys.J. 492 (1998) 554-568
Astronomy and Astrophysics
Astrophysics
41 pages (Latex) including 6 Figures and 2 Tables. Final Revised Version changes to text, tables and figures. ApJ, 492, in pre
Scientific paper
10.1086/305070
Sgr A* at the Galactic Center is a puzzling source. It has a mass M=(2.5+/-0.4) x 10^6 solar masses which makes it an excellent black hole candidate. Observations of stellar winds and other gas flows in its vicinity suggest a mass accretion rate approximately few x 10^{-6} solar masses per year. However, such an accretion rate would imply a luminosity > 10^{40} erg/s if the radiative efficiency is the usual 10 percent, whereas observations indicate a bolometric luminosity <10^{37} erg/s. The spectrum of Sgr A* is unusual, with emission extending over many decades of wavelength. We present a model of Sgr A* which is based on a two-temperature optically-thin advection-dominated accretion flow. The model is consistent with the estimated mass and accretion rate, and fits the observed fluxes in the cm/mm and X-ray bands as well as upper limits in the sub-mm and infrared bands; the fit is less good in the radio below 86 GHz and in gamma-rays above 100 MeV. The very low luminosity of Sgr A* is explained naturally in the model by means of advection. Most of the viscously dissipated energy is advected into the central mass by the accreting gas, and therefore the radiative efficiency is extremely low, approximately 5 x 10^{-6}. A critical element of the model is the presence of an event horizon at the center which swallows the advected energy. The success of the model could thus be viewed as confirmation that Sgr A* is a black hole.
Gammie Charles
Grindlay Jonathan E.
Mahadevan Rohan
Narayan Ramesh
Popham Robert G.
No associations
LandOfFree
Advection-Dominated Accretion Model of Sagittarius A*: Evidence for a Black Hole at the Galactic Center does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Advection-Dominated Accretion Model of Sagittarius A*: Evidence for a Black Hole at the Galactic Center, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Advection-Dominated Accretion Model of Sagittarius A*: Evidence for a Black Hole at the Galactic Center will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-466352