A size of ∼1 au for the radio source Sgr A* at the centre of the Milky Way

Abstract

Table 1 for details.

High Resolution Imaging of Sagittarius A*

“…Turbulent electrons along the line of sight to Sgr A*, however, scatter radio wavelength photons and produce an image that is an elliptical Gaussian with a major axis size of ∼ 0.5 arcsec at 20 cm and a λ 2 dependence [2]. Separating the effects of the small intrinsic source from the effects of scattering has required observations at short wavelengths, careful calibration, and the use of closure amplitude techniques, which reduce sensitivity but remove uncertainty due to calibration error [3,4]. These efforts have recently resulted in the first robust detections of intrinsic structure in Sgr A* at wavelengths of 1.3 cm, 0.7 cm and 0.35 cm.…”

“…For the larger scattering size, we cannot measure the intrinsic size at wavelengths longer than 1.3 cm and find a shallower power-law index of γ = 1.3 ± 0.2. Triangles are VLBA measurements determined through closure amplitude analysis from [3] and [4]. Squares are the new VLA+PT measurements.…”

Understanding our Galaxy: from the center to outskirts

“…By fitting the apparent sizes measured at five wavelengths quasi-simultaneously, we were able to revise the 2-dimensional scattering structure (Shen et al 2005). Then, by subtracting in quadrature the extrapolated scattering size, we successfully detected the intrinsic size of Sgr A* at 3.5 mm to be ≈1 AU in diameter.…”

“…Then, by subtracting in quadrature the extrapolated scattering size, we successfully detected the intrinsic size of Sgr A* at 3.5 mm to be ≈1 AU in diameter. Together with a lower limit on the mass of Sgr A* of 0.4 × 10 6 solar masses from the study of the proper motion of Sgr A* itself (Reid & Brunthaler 2004), a size of 1 AU sets an extraordinarily high mass density for Sgr A*, strongly arguing for the SMBH nature of Sgr A* (Shen et al 2005).…”

“…With high-resolution millimeter-VLBI observations, Shen et al (2005) have measured the intrinsic size of the radio-emitting region of the galactic center compact radio source Sgr A* to be only 1 AU in diameter at 3.5 mm. When combined with the lower limit on the mass of Sgr A*, this provides strong evidence for Sgr A* being a super-massive black hole.…”