New structures near the compact radio source at the Galactic Centre

Abstract

SIXTEEN years ago, Balick and Brown¹ found a bright compact radio source, Sgr A^*, at the Galactic Centre, as had been predicted by Lynden-Bell and Rees². The characteristics of its emission and the kinematics of gas near it have been used to argue for the presence of a black hole of 500–5 x 10⁶ solar masses at the Galactic Centre^3–5. Here we present high-resolution (<0.2 arcsec) radio images, made at 2-cm wavelength, of the central arcsecond of the Galaxy. Sgr A^* is surrounded by at least four satellite radio features. Interpreted as thermally emitting blobs of plasma, they have typical sizes <1,700 AU and are within a projected distance of 3,500 AU from Sgr A^*. Another set of larger radio features, 2–4 arcsec from Sgr A^*, shows a regular progression of galactocentric distance with position angle. The placement and appearance of all these structures lead us to suggest that they are physically associated with Sgr A^*; if so, they can be used as probes of the immediate vicinity of the possible massive black hole at the Galactic Centre.