Work

Evidence for Low Black Hole Spin and Physically Motivated Accretion Models From Millimeter-vlbi Observations of Sagittarius A*

Year: 2011

Type: article

Abstract: Millimeter very long baseline interferometry (mm-VLBI) provides the novel capacity to probe the emission region of a handful of supermassive black holes on sub-horizon scales. For Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, this provides access to the region in the immediate vicinity of the horizon. Broderick et al. have already shown that by leveraging spectral and polarization information as well as accretion theory, it is possible to extract accretion-model parameters (including black hole spin) from mm-VLBI experiments containing only a handful of telescopes. Here we repeat this analysis with the most recent mm-VLBI data, considering a class of aligned, radiatively inefficient accretion flow (RIAF) models. We find that the combined data set rules out symmetric models for Sgr A*'s flux distribution at the 3.9σ level, strongly favoring length-to-width ratios of roughly 2.4:1. More importantly, we find that physically motivated accretion flow models provide a significantly better fit to the mm-VLBI observations than phenomenological models, at the 2.9σ level. This implies that not only is mm-VLBI presently capable of distinguishing between potential physical models for Sgr A*'s emission, but further that it is sensitive to the strong gravitational lensing associated with the propagation of photons near the black hole. Based upon this analysis we find that the most probable magnitude, viewing angle, and position angle for the black hole spin are a = 0.0 +0.64 + 0.86 , , and east of north, where the errors quoted are the 1σ and 2σ uncertainties.

Source: The Astrophysical Journal

DOI: 10.1088/0004-637x/735/2/110

Authors: Avery E. Broderick, Vincent L. Fish, Sheperd S. Doeleman, Abraham Loeb

Institutions: Canadian Institute for Theoretical Astrophysics, Massachusetts Institute of Technology, Harvard University, Center for Astrophysics Harvard & Smithsonian

Language: English

Topic: Astrophysical Phenomena and Observations

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: bronze

Funders: National Science Foundation, National Aeronautics and Space Administration