Approaching the event horizon: 1.3mm VLBI of SgrA*

TL;DR

This paper reports high-resolution 1.3mm VLBI observations of SgrA* that reveal structures on scales comparable to the event horizon, demonstrating the potential of mm/sub-mm VLBI for black hole physics.

Contribution

It presents the first confirmation of SgrA* structure at a few Schwarzschild radii using short wavelength VLBI, advancing observational capabilities.

Findings

Measured SgrA* diameter as 37 micro arcsec

Observed structure smaller than the expected event horizon size

Demonstrated the feasibility of mm/sub-mm VLBI for black hole studies

Abstract

Advances in VLBI instrumentation now allow wideband recording that significantly increases the sensitivity of short wavelength VLBI observations. Observations of the super-massive black hole candidate at the center of the Milky Way, SgrA*, with short wavelength VLBI reduces the scattering effects of the intervening interstellar medium, allowing observations with angular resolution comparable to the apparent size of the event horizon of the putative black hole. Observations in April 2007 at a wavelength of 1.3mm on a three station VLBI array have now confirmed structure in SgrA* on scales of just a few Schwarzschild radii. When modeled as a circular Gaussian, the fitted diameter of SgrA* is 37 micro arcsec (+16,-10; 3-sigma), which is smaller than the expected apparent size of the event horizon of the Galactic Center black hole. These observations demonstrate that mm/sub-mm VLBI is poised to open a new window onto the study of black hole physics via high angular resolution observations of the Galactic Center.