Abstract
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 ∼3 × 1016 cm) and then through a small accretion disk at ≲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 ∼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 ≲ v ≲ 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.
| Original language | English (US) |
|---|---|
| Journal | Astrophysical Journal |
| Volume | 443 |
| Issue number | 1 PART 2 |
| State | Published - Apr 10 1995 |
Fingerprint
Keywords
- Accretion, accretion disks
- Black hole physics
- Galaxy: center
- Relativity
ASJC Scopus subject areas
- Space and Planetary Science
Cite this
The effects of redshifts and focusing on the spectrum of an accretion disk in the Galactic center black hole candidate sagittarius A. / Hollywood, J. M.; Melia, Fulvio.
In: Astrophysical Journal, Vol. 443, No. 1 PART 2, 10.04.1995.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - The effects of redshifts and focusing on the spectrum of an accretion disk in the Galactic center black hole candidate sagittarius A
AU - Hollywood, J. M.
AU - Melia, Fulvio
PY - 1995/4/10
Y1 - 1995/4/10
N2 - 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 ∼3 × 1016 cm) and then through a small accretion disk at ≲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 ∼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 ≲ v ≲ 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.
AB - 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 ∼3 × 1016 cm) and then through a small accretion disk at ≲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 ∼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 ≲ v ≲ 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.
KW - Accretion, accretion disks
KW - Black hole physics
KW - Galaxy: center
KW - Relativity
UR - http://www.scopus.com/inward/record.url?scp=11944261678&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=11944261678&partnerID=8YFLogxK
M3 - Article
AN - SCOPUS:11944261678
VL - 443
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1 PART 2
ER -