The effects of redshifts and focusing on the spectrum of an accretion disk in the galactic center black hole candidate Sagittarius A*

Details The effects of redshifts and focusing on the spectrum of an accretion disk in the galactic center black hole candidate Sagittarius A* The effects of redshifts and focusing on the spectrum of an accretion disk in the galactic center black hole candidate Sagittarius A*

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...443l..17h&link_type=abstract

Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 443, no. 1, p. L17-L20

Astronomy and Astrophysics

Astronomy

11

Accretion Disks, Black Holes (Astronomy), Radio Sources (Astronomy), Red Shift, Sagittarius Constellation, Spectrum Analysis, Flux Density, Light Speed, Relativity, Schwarzschild Metric

Scientific paper

There are firm indications that Sgr A*, a compact, nonthermal radio source at the Galactic center, may be powered by the dissipation of gravitational energy as gas trapped from an ambient wind descends down the potential well, first through a quasi-spherical inflow (extending out to approximately 3 x 1016 cm) and then through a small accretion disk at less than or approximately = 5-10 Schwarzschild radii. Earlier three-dimensional Bondi-Hoyle numerical simulations have indicated that fluctuations in the accreted specific angular momentum can lead to a variability in the disk flux on a timescale of years. With greatly improved flux measurements at K and H, and the hint of a approximately 10 minute modulation in the IR luminosity, it is crucial to model the disk emission much more precisely than has been attempted thus far. In this Letter we take into account the effects of Doppler and gravitational redshifts, the light-travel time factor, and the light bending near the black hole to determine the measurable spectrum of Sgr A* in the increasingly important 1013 Hz less than or approximately = v less than or approximately = 1016 Hz frequency range. We find that the relativistic disk spectrum is much softer than its Newtonian counterpart, with a predicted UV flux roughly an order of magnitude smaller than had previously been anticipated. In addition, we find that when the physical conditions in the disk are taken to be consistent with the properties of the quasi-spherical infall (specifically, in terms of the accretion rate and disk size), only a slowly spinning or Schwarzschild black hole appears to fit the observations. Our calculations also reveal that the disk flux is much more weakly dependent on the observer's inclination angle than had been suspected on the basis of earlier Newtonian estimates.

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