Stellar Gas Flows Into A Dark Cluster Potential At The Galactic Center

Abstract

The evidence for the presence of a concentration of dark matter at the Galactic center is now very compelling. There is no question that the stellar and gas kinematics within 0.01 pc is dominated by under-luminous matter in the form of either a massive black hole, a highly condensed distribution of stellar remnants, or a more exotic source of gravity. The unique, compact radio source Sgr A* appears to be coincident with the center of this region, but its size (less than 3x10^14 cm at lambda=1.35cm) is still significantly smaller than the current limiting volume enclosing this mass. Sgr A* may be the black hole, if the dark matter distribution is point-like. If not, we are left with a puzzle regarding its nature, and a question of why this source should be so unique and lie only at the Galactic center. Here, we examine an alternative to the black hole paradigm---that the gravitating matter is a condensed cluster of stellar remnants---and study the properties of the Galactic center wind flowing through this region. Some of this gas is trapped in the cluster potential, and we study in detail whether this hot, magnetized gas is in the proper physical state to produce Sgr A*'s spectrum. We find that at least for the Galactic center environment, the temperature of the trapped gas never attains the value required for significant GHz emission. In addition, continuum (mostly bremsstrahlung) emission at higher frequencies is below the current measurements and upper limits for this source. We conclude that the cluster potential is too shallow for the trapped Galactic center wind to account for Sgr A*'s spectrum, which instead appears to be produced only within an environment that has a steep-gradient potential like that generated by a black hole.

27 pages, including 1 table and 8 EPS figures; submitted to ApJ; uses aasms4.sty

References in corpus (3)

• Dynamical Constraints On Alternatives To Massive Black Holes In Galactic Nuclei
• Hydrodynamical Accretion Onto Sgr A* From Distributed Point Sources
• 7 mm lambda VLBA Observations of Sagittarius A*

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• A Possible Rossby Wave Instability Origin for the Flares in Sagittarius A*
• Diffuse X-Rays from the Inner 3 Parsecs of the Galaxy
• Simultaneous Multi-Wavelength Observations of Sgr A*
• The Linear Polarization of Sagittarius A* II. VLA and BIMA Polarimetry at 22, 43 and 86 GHz
• High Spectral Resolution Observations of the Massive Stars in the Galactic Center
• General Relativistic Flux Modulations from Disk Instabilities in Sagittarius A*
• The Role of Magnetic Field Dissipation in the Black Hole Candidate Sgr A*
• Effect of an isotropic outflow from the Galactic centre on the bow-shock evolution along the orbit
• Where have all the black holes gone?
• A Numerical Assessment of Cosmic-ray Energy Diffusion through Turbulent Media
• Microlensing in phase space I: Continuous propagation of variability moments